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Operating Manual MHX-920 900 MHz Spread Spectrum OEM Transceiver Revision 1.20, December 21, 2000 Microhard Systems Inc.
#110, 1144 - 29th Ave. N.E. Calgary, Alberta T2E 7P1 Phone: (403) 248-0028 Fax: (403) 248-2762 www.microhardcorp.com MHX-920 900 MHz Spread-Spectrum Embedded Modem WARNING In order to comply with the FCC/IC adopted RF exposure requirements, this transmitter system will be installed by the manufacturer's reseller professional. Installation of all antennas must be performed in a manner that will provide at least 23 cm clearance from the front radiating aperture, to any user or member of the public. EQUIPMENT LABELING The manufacturer, product name, and FCC and Industry Canada identifiers of this product must appear on the outside label of the end-user equipment. l This manual contains information of proprietary interest to Microhard Systems Inc. It has been supplied in confidence to purchasers and users of the MHX-920, and by accepting this material the recipient agrees that the contents will not be copied or reproduced, in whole or in part, without prior written consent of Microhard Systems Inc. Microhard Systems Inc. has made every effort to assure that this document is accurate and complete. However, the company reserves the right to make changes or enhancements to the manual and/or the product described herein at any time and without notice. Furthermore, Microhard Systems Inc. assumes no liability resulting from any omissions in this document, or out of the application or use of the device described herein. Microhard Systems products are appropriate for home, office, or industrial use, but are not authorized for utilization in applications where failure could result in damage to property or human injury or loss of life. The electronic equipment described in this manual generates, uses, and radiates radio frequency energy. Operation of this equipment in a residential area may cause radio interference, in which case the user, at his own expense, will be required to take whatever measures necessary to correct the interference. FCC Declaration of Conformity This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) this device may not cause harmful interference, and (2) this device must accept any interference received including interference that may caused undesired operation. Microhard Systems Inc.s products are warranted against all failures which occur as a result of defective material or workmanship within 12 months of purchase by the user. This warranty does not extend to products that, in the opinion of Microhard Systems Inc., have been subject to misuse, accidents, lightning strikes, improper installation or application, nor shall it extend to units which have, in Microhard Systems Inc.s opinion, been opened, tampered with or repaired by an unauthorized facility. Microhard Systems Inc. Leaders in Wireless Telecom
#110, 1144 - 29th Ave. N.E. Calgary, Alberta T2E 7P1 Phone: (403) 248-0028 Fax: (403) 248-2762 www.microhardcorp.com 2000 by Microhard Systems Inc., All Rights Reserved. HyperTerminal is copyrighted by Hilgraeve Inc, and developed for Microsoft. Microsoft and Windows are registered trademarks of Microsoft Corporation. pcANYWHERE and Symantec are registered trademarks of Symantec Corp. All other products mentioned in this document are trademarks or registered trademarks of their respective holders. Manual Revision 1.20, December 21, 2000. ii MHX-920 Operating Manual Contents Product Overview .............................................................................................................................................................................. 1 Features.............................................................................................................................................................................................. 1 About this Manual ............................................................................................................................................................................. 2 Introduction 1.0 1.1 1.2 Electrical/Physical Functional Block Diagram................................................................................................................................................................. 3 2.0 Pinout................................................................................................................................................................................................. 4 2.1 LED Operation................................................................................................................................................................................... 6 2.2 DC Characteristics ............................................................................................................................................................................. 8 2.3 2.4 AC Characteristics .............................................................................................................................................................................. 9 Modes of Operation ..................................................................................................................................................................................... 11 Data Mode ........................................................................................................................................................................................ 11 3.1 3.2 Command Mode ............................................................................................................................................................................... 12 3.2.1 AT Command Interface ....................................................................................................................................................... 13 Switching Between Command and Data Modes ............................................................................................................................... 13 1. 2. 3. 4. 3.3 Configuration 4.1 4.2 4.3 Quick Start Approach ...................................................................................................................................................................... 15 AT Commands................................................................................................................................................................................. 16 A - Answer........................................................................................................................................................................................ 17 E - Command Echo.......................................................................................................................................................................... 17 I - Identification ............................................................................................................................................................................... 17 O - Online Mode.............................................................................................................................................................................. 17 Q - Quiet Mode................................................................................................................................................................................ 17 V - Result Codes Display................................................................................................................................................................. 17 W - Connection Result..................................................................................................................................................................... 18 Z - Reset Modem and load stored configuration .............................................................................................................................. 18
&C - DCD (Data Carrier Detect) ..................................................................................................................................................... 18
&D - DTR (Data Terminal Ready)................................................................................................................................................... 18
&F - Load Factory default configuration ......................................................................................................................................... 18
&K - Handshaking............................................................................................................................................................................ 18
&S - DSR (Data Set Ready)............................................................................................................................................................. 19
&V - View Configuration ................................................................................................................................................................. 19
&E - Framing Error Check................................................................................................................................................................ 19
&W - Write Configuration to memory............................................................................................................................................. 19 Sxxx? - Read S register value........................................................................................................................................................... 19 Sxxx=yyy - Set S register value ....................................................................................................................................................... 19 Command Result Codes................................................................................................................................................................... 20 S Registers ....................................................................................................................................................................................... 21 S Register 2 - Escape Code............................................................................................................................................................... 21 S Register 3 - CR Control Code....................................................................................................................................................... 21 S Register 4 - Linefeed Control Code .............................................................................................................................................. 21 S Register 5 - Backspace Control Code ........................................................................................................................................... 21 S Register 101 - Operating Mode..................................................................................................................................................... 22 S Register 102 - Serial Baud Rate.................................................................................................................................................... 24 S Register 103 - Wireless Link Rate ................................................................................................................................................ 24 S Register 104 - Network Address ................................................................................................................................................... 25 S Register 105 - Unit Address.......................................................................................................................................................... 25 S Register 106 - Primary Hopping Pattern....................................................................................................................................... 25 S Register 206 - Secondary Hopping Pattern .................................................................................................................................... 25 S Register 107 - Encryption Key...................................................................................................................................................... 27 S Register 108 - Output Power Level............................................................................................................................................... 27 S Register 109 - Hopping Interval.................................................................................................................................................... 28 S Register 110 - Data Format............................................................................................................................................................ 29 S Register 111 - Packet Minimum Size ............................................................................................................................................ 29 S Register 112 - Packet Maximum Size............................................................................................................................................ 29 S Register 114 - Packet Size Control ................................................................................................................................................ 29 S Register 116 - Packet Character Timeout ...................................................................................................................................... 29 S Register 113 - Packet Retransmissions .......................................................................................................................................... 30 S Register 213 - Packet Retry Limit.................................................................................................................................................. 31 S Register 115 - Packet Repeat Interval........................................................................................................................................... 31 S Register 117 - Modbus Mode ........................................................................................................................................................ 32 S Register 118 - Roaming................................................................................................................................................................. 33 S Register 119 - Quick Enter to Command....................................................................................................................................... 33 iii MHX-920 Operating Manual S Register 120 - RTS/DCD Framing................................................................................................................................................. 33 S Register 121 - DCD Timeout......................................................................................................................................................... 33 S Register 122 - Remote Control ...................................................................................................................................................... 34 S Register 123 - RSSI Reading ......................................................................................................................................................... 34 4.4 Diagnostics, Statistics and Remote Control ...................................................................................................................................... 35 4.4.1 Spectrum Analyzer Feature ............................................................................................................................................................... 35 4.4.2 Statistics............................................................................................................................................................................................ 35 4.4.3 Remote Control and Diagnostics ...................................................................................................................................................... 36 Installation ................................................................................................................................................................................................... 39 Estimating the Gain Margin.............................................................................................................................................................. 39 5.1 5.2 Antennas and Cabling....................................................................................................................................................................... 41 5.2.1 Internal Cabling ................................................................................................................................................................................ 41 5.2.2 Installing External Cables, Antennas and Lightning Arrestors.......................................................................................................... 42 Modem Command Summary ...................................................................................................................................................................... 45 Serial Interface ............................................................................................................................................................................................ 47 Sample Schematic Diagram ........................................................................................................................................................................ 49 Factory Default Settings.............................................................................................................................................................................. 51 Performance Tables...................................................................................................................................................................................... 53 Hopping Tables............................................................................................................................................................................................ 55 Technical Specifications ............................................................................................................................................................................. 57 Mechanical Drawing.................................................................................................................................................................................... 59 Glossary ...................................................................................................................................................................................................... 61 MHX-920 Operating Manual 5. A. B. C. D. E F. G. H. I. iv 1. Introduction 1.0 Product Overview The MHX-920 is a high-performance embedded wireless data transceiver. Operating in the 902 - 928 MHz ISM band, this frequency-hopping spread-
spectrum module is capable of providing reliable wireless data transfer between almost any type of equipment which uses an asynchronous serial interface. The small-size and superior RF performance of this module make it ideal for many applications. Typical uses for this module include:
n SCADA n Traffic Control n Remote Monitoring n Fleet Management;
n Telemetry;
n Remote Camera/Robot Control;
n Security Systems; and, n Display Signs. While a pair of MHX-920 modules can link two terminal devices (point-to-
point operation), multiple modules can be used together to create a network of various including point-to-multipoint and repeater operation. Multiple independent networks can operate concurrently, so it is possible for unrelated communications to take place in the same or a nearby area without sacrificing privacy or reliability. topologies, 1.1 Features Key features of the MHX-920 include:
n transmission within a public, license-exempt band of the radio spectrum1 this means that it can be used without access fees
(such as those incurred by cellular airtime);
n a serial I/O data port with handshaking and hardware flow control, allowing the MHX-920 to interface directly to any equipment with an asynchronous serial interface. 1 902-928 MHz, which is license-free within North America; may need to be factory-configured differently for some countries. MHX-920 Operating Manual: Chapter 1 Introduction. 1 n 64 sets of user-selectable pseudo-random hopping patterns, intelligently designed to offer the possibility of separately operating multiple networks while providing security, reliability and high tolerance to interference;
n encryption key with 65536 user-selectable values to maximize security and privacy of communications;
n built-in CRC-16 error detection and auto re-transmit to provide 100% accuracy and reliability of data;
n ease of installation and use the MHX-920 module uses a subset of standard AT style commands, very similar to those used by traditional telephone line modems. While the typical application for the MHX-920 is to provide a short- to mid-
range wireless communications link between DTEs, it can be adapted to almost any situation where an asynchronous serial interface is used and data intercommunication is required. 1.2 About this Manual This manual has been provided as a guide and reference for installing and using MHX-920 wireless modem modules. The manual contains instructions, suggestions, and information which will help you set up and achieve optimal performance from your equipment using the MHX-920 module. It is assumed that users of the MHX-920 module have either system integration or system design experience. the electrical/physical attributes of the module. Chapter 3 explains the different modes of operation. Chapter 4 provides complete details of all configuration parameters; and, Chapter 5 is an installation/deployment guide. The Appendices, including the Glossary of Terms, are provided as informational references which you may find useful throughout the use of this manual as well as during the operation of the wireless modem. Chapter 2 details Throughout the manual, you will encounter not only illustrations that further elaborate on the accompanying text, but also several symbols which you should be attentive to:
Caution or Warning: Usually advises against some action which could result in undesired or detrimental consequences. Point to Remember: Highlights a key feature, point, or step which is worth noting, Keeping these in mind will make using the MHX-920 more useful or easier to use. Tip: An idea or suggestion is provided to improve efficiency or to make something more useful. With that in mind, enjoy extending the boundaries of your communications with the MHX-920 module. 2 MHX-920 Operating Manual: Chapter 1 Introduction 2. Electrical/Physical 2.0 Functional Block Diagram DVcc AVcc GND
\Config
\Reset TxD RTS DTR Mixer LNA IF Demod Antenna Switch
+-
Comparator Frequency Synthesizer PA GAIN Mixer uC A/D SRAM SRAM EEPROM 8 bit data bus UART
(DCE) RSSI1-3 RXMODE TXMODE RxD CTS DSR DCD Figure 1. Functional Block Diagram MHX-920 Operating Manual: Chapter 2 Electrical/Physical 3 2.1 Pinout Figure 2 provides a top-view pinout drawing of the MHX-920 module. The corner pins (1,20,21,40) are labeled directly on the module. MHX-910 AVcc AVcc DVcc DVcc DVcc DVcc DVcc NC
\Config
\Reset GND GND GND GND GND GND GND NC NC NC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 NC NC NC NC NC NC NC Rx/SYNC TxMODE RSSI3 RSSI2 RSSI1 CTS RTS DSR NC DTR TxD RxD DCD Figure 2 - Pinout (Top View) Table 1. Pin Description Pin Name AVcc No. 1,2
\Config CTS DCD DSR DTR 9 28 21 26 24 DVcc 3-7 Description Positive Supply for Radio Circuitry. See Section 2.3 for DC Characteristics Leave unconnected. For factory use only. Do not ground RS-232 Clear to Send. Active low (TTL level) output. See Appendix B for a complete description of all RS-232 signals. RS-232 Data Carrier Detect. Active low (TTL level) output. RS-232 Data Set Ready. Active low (TTL level) output. RS-232 Data Terminal Ready. Active low
(TTL level) input. Positive Supply for Logic circuitry and I/O pins. See Section 2.3 for DC Characteristics I/O I O O O I I 4 MHX-920 Operating Manual: Chapter 2 Electrical/Physical Table 1 (continued) GND 11-17
\Reset RSSI1 10 29 RSSI2 30 RSSI3 31 RTS RxD RX/SYNC TxD TXMODE 27 22 33 23 32 Ground reference for logic, radio and I/O pins. Active low reset input to the module. See Section 2.4 for timing information. Receive Signal Strength Indicator 1. This output is the first of the three RSSI indicators to become active high as the signal strength increases. See Section 2.2 for details Receive Signal Strength Indicator 2. This output is the second RSSI indicator to become active high as the signal strength increases. See Section 2.2 for details. Receive Signal Strength Indicator 3. This output is the last RSSI indicator to become active high as the signal strength increases. See Section 2.2 for details. RS-232 Request to Send. Active low (TTL level) input. RS-232 Receive Data. TTL level output. Active high output indicates receive and synchronization status. See Section 2.2. RS-232 Transmit Data. TTL level input. Active high output indicates module is transmitting data over the RF channel. See Section 2.2. I O O O I O O I O MHX-920 Operating Manual: Chapter 2 Electrical/Physical 5 2.2 LED OPERATION LED functionality is dependent on the mode of operation. Lines RX/SYNC, TXMODE, and RSSI1,2 and 3 are designed to drive LEDs (active high). Table 2 explains LED operation for the various modes. Table 2. LED Operation MODE RX/Sync TXMode RSSI1,2,3 LED Power Up (S0=1, S119=1) Power Up (S0=1, S119=0) Power Up (S0=0) Command Mode Data Mode - Master off off off off on while receiving valid data packets from slaves and repeaters in the network off off off off blink 500ms on/500ms off off off off on for the first portion of each hop interval. RSSI mode based on all received packets Data Mode - Repeater During Sync. Acquisition off off Data Mode - Repeater When Synchronized on for first portion of hop interval Data Mode - Slave During Sync. Acquisition Data Mode - Slave When Synchronized off on on for second portion of hop interval off See Table 3 alternating 300ms on RSSI mode based on packets received from Slaves*
See Table 3 alternating 300ms on on when transmitting a packet. RSSI mode based on packets received from the Repeater or Master with which it communicates See Table 3
*If Slaves have been silent for 2 seconds, repeater will base its RSSI on packets received from the Master. 6 MHX-920 Operating Manual: Chapter 2 Electrical/Physical Signal strength, which is also reported in Register S123, is calculated based on the last four valid received packets with correct CRC, and represented by RSSI1, 2 and 3. For slaves, packets are received on every single hop either from a repeater, or the master. When calculating RSSI, the master takes into consideration all packets received from slaves and repeaters. Repeaters and slaves only transmit back to the master when they have information to send. Therefore, if no data is coming back to the master then RSSI will never get updated at the master, and the LEDs will be off. Table 3 - RSSI mode operation Signal Strength
(dBm)
-108
-101
-93
-86
-79
-71 RSSI1 RSSI2 RSSI3 50% duty cycle on solid on solid on solid on solid on solid off off 50% duty cycle on solid on solid on solid off off off off 50% duty cycle on solid MHX-920 Operating Manual: Chapter 2 Electrical/Physical 7 2.3 DC Characteristics Sym Characteristic AVCC DVCC VPOT VRST AICCR AICCT 0 AICCT 1 AICCT 2 AICCT 3 DICC VIL VIH VOL VOH Radio Supply Voltage Logic Supply Voltage Power On Reset Threshold Voltage Reset Pin Threshold Voltage Radio Supply Current in Receive Mode Radio Supply Current at 1mW Transmit Min 4.9 4.75 1.8 96 68 Radio Supply Current at 10mW Transmit 111 Radio Supply Current at 100mW Transmit 157 Radio Supply Current at 1W Transmit Logic Supply Current Input Low Voltage (Pins 23,24,27) 398 95
-0.5 Input High Voltage (Pins 23,24,27) 0.6VCC Output Low Voltage (Pins 21,22,26,28-
33) Output High Voltage (Pins 21,22,26,28-
33) 4.2 Typ Max Units 5.0 5.0 2 DVCC/
2 107 108 123 174 442 105 5.5 5.5 2.2 117 119 V V V V mA mA 135 mA 191 mA 486 mA 115 mA
.3DVCC VCC+.5 0.6 V V V V ISRCE Sourcing Current (Pins 21,22,26,28-33) 10 mA IMPORTANT:
For best performance, it is strongly recommended to use a separate, linearly regulated supply for Vcc Radio. Do not directly feed a switching power supply into Vcc Radio. For OEM design simplicity, connect both the radio and logic Vcc connections together. Caution: Using any other power supply which does not provide the proper voltage or current could damage the MHX-920 module. 8 MHX-920 Operating Manual: Chapter 2 Electrical/Physical 2.4 AC Characteristics Sym Characteristic TTOUT Reset Delay Time-Out Period TR2D TR2C Internal Reset to Data Mode*
Internal Reset to Command Mode Min 0 Typ 500 0 Max Units 5 ms s ms
*Unit will enter into Command Mode upon power up if register S0=0. Unit will enter into Data Mode upon power-up if register S0=1. When powering up into Data Mode, an additional delay of 5 seconds is added if Register S119=1. See page 14 for details. Figure 3 provides timing information for both power-up reset and the \Reset line operation. A fixed internal reset delay timer of roughly 500ms is triggered as the VPOT or VRST threshold is reached. DV CC
\Reset V POT V RST Internal Reset T TOUT Data Mode
(Valid when S0=1) Command Mode
(Valid when S0=0) Figure 3. Reset Timing T R2D T R2C MHX-920 Operating Manual: Chapter 2 Electrical/Physical 9 10 MHX-920 Operating Manual: Chapter 3 Modes of Operation 3. Modes of Operation The MHX-920 modem can be easily configured to meet a wide range of needs and applications. The module is designed such that all communication is through one serial port (Pins 21 to 28 on the module). This port has two functions:
1. It provides the asynchronous interface with the host equipment for data that is sent/received on the RF channel. When operating in this fashion, the module is said to be in data mode. 2. It is also used for configuring and programming the module. When operating in this fashion, the module is said to be in command mode. In addition to data mode and command mode, there is a third mode of operation called diagnostics mode. The module will always be in one of these three modes. 3.1 Data Mode Data mode is the normal operating mode of the MHX-920. When in data mode, the MHX-920 is communicating with other MHX-920 modules, and facilitating wireless asynchronous serial communication amongst two or more terminal devices. There are three basic elements to any MHX-920 communications network:
One module configured as the Master Zero or more modules configured as Repeaters One or more modules configured as Slaves The function of the Master is to provide synchronization for the entire network, and to control the flow of data. There is always one Master per network. The Master is the ultimate destination for all data collected at the various Repeaters and Slaves serial ports. With the network set up for Point-to-Multipoint communication, all data received at the Masters serial port is transmitted to every Repeater and Slave in the network. The MHX-
920 is a frequency hopping transceiver, meaning that it hops to a new frequency after a predetermined time interval. This time interval is a fixed time set by the user, and can range from 8ms to 120ms. The MHX-920 hops according to a pseudorandom pattern of 50 different channels. When configured as a Slave, the MHX-920 searches for synchronization with a Master. Network topologies consisting of a single Master and virtually any combination of Slaves and Repeaters may be deployed. The functionality of any follows:
particular MHX-920 configured can be as MHX-920 Operating Manual: Chapter 3 Modes of Operation 11 M Network 1 S M M Network 2 R R S M S Network 3 M R S Network 4 M R Network 5 S S S S S S R S Figure 4 - Sample Network Topologies. Virtually any Combination of Slaves and Repeaters May be Used. n Master Point-to-Point: The modem is configured to communicate with a single Slave, either directly, or through one or more Repeaters. n Master Point-to-Multipoint: The modem is configured to communicate with one or more Slaves and/or Repeaters. n Slave: The modem is configured to communicate with one Master either directly or through one or more Repeaters.. n Repeater: The modem is configured to pass information from either a Master or another Repeater onto subsequent Repeaters and/or Slaves and vice versa. The Repeater also acts as a Slave in the sense that, like a Slave, it passes information to/from its serial port. Examples of different network topologies are shown in Figure 4. Network 1 shows Point-to-Point communication between a Master and Slave. Network 2 makes use of a Repeater to communicate with the Slave. Network 3 illustrates a simple Point-to-Multipoint network with no Repeaters. Networks 4 and 5 gives examples of Point-to-Multipoint networks consisting of both Repeaters and Slaves. There is effectively no restriction to the number of Repeaters and Slaves that can be added to a network. As seen in Network 4, a Master can communicate directly with both Slaves and Repeaters. 3.2 Command Mode The MHX-920 firmware has been designed to allow the user to customize the operation of the modem through an AT Command Interface. This interface is ideal for direct interface with another microcontroller or for higher level Windows-based software applications, but also contains user-friendly built-in register descriptions. These descriptions make it easy for the user to configure the unit by manually inputting AT Commands and modifying S-
Register parameters, using any standard terminal program. The MHX-series development board is a useful tool for familiarizing yourself with the various operating parameters and user interface. Reference schematics for the development board can be found in Appendix G. To access the MHX-920s command mode using the development board:
1. Insert the module into the socket with the antenna connector towards the edge of the board. 2. Attach the supplied antenna. 3. Connect a straight through serial cable between the DB9 connector and the serial port on your PC 4. Run any terminal application program such as Hyperterminal 5. Set the serial port to 9600 baud, 8N1 6. Apply power to the development board 7. While the three RSSI LEDs are blinking, type mhx (you have about 5 seconds to do this). The modem should respond with OK. 8. Type AT&V <ENTER>
12 MHX-920 Operating Manual: Chapter 3 Modes of Operation 3.2.1 AT Command Interface At this point you should see a menu similar to the following appear:
BAUD = 9600 E1 Q0 V1 W0 DCD &C1 DTR &D0 Framing &E0 Handshaking &K3 DSR &S1 S0=1 S2=43 S3=13 S4=10 S5=8 Operating Mode S101=1 Serial Baud Rate S102=7 Wireless Link Rate S103=2 Network Address S104=1 Unit Address S105=1 Hop Pattern S106=0 Encryption Key S107=1 Output Power S108=2 Hop Interval S109=4 Data Format S110=1 Packet Min Size S111=1 Packet Max Size S112=43 Packet Retransmissions S113=1 Quick enter to command S119=1 Packet Repeat Interval S115=1 Character Timeout, ms S116=8 RTS/DCD Framing, ms S120=0 DCD Timeout, ms S121=0 Secondary Hop Pattern S206=2 Packet Retry Limit S213=2 Average RSSI value S123= -0 dBm Modbus Mode S117=0 Roaming S118=0 Packet Size Control S114=0 Remote Control S122=0 OK The MHX-920 is controlled through an AT Command line interface using a command set which is very similar to a traditional Hayes telephone modem command set. All line entries must be preceded by the characters AT. The characters AT are known as the attention characters and must be typed at the beginning of each command line. For example, to change the operating mode, type:
ATS101=2 <ENTER>
The modem should respond with OK. The above command will set the operating mode to Master Point-to-Point. Register settings are not immediately stored to non-volatile memory, therefore if the modem is powered down at this point, the Operating Mode would revert to its previous value. To store any recently updated command registers, the following write command must be entered. AT&W <ENTER>
3.3 Switching Between Command and Data Modes Your modem must be in command mode for it to execute a command. If you send characters when the modem is in data mode, the modem transmits the characters over the air. Depending on its settings, the modem will either power up in command mode or data mode. Normally, when first received from the factory, the unit will power up into data mode. During the first five seconds after power-up, the user is given the opportunity to avoid entering into data mode but instead enter into command mode by typing mhx. MHX-920 Operating Manual: Chapter 3 Modes of Operation 13 DATA MODE mand) A or ATO Com Escape Sequence DTR or
(AT 5 sec elapses or characters other than
'mhx'
entered by the user COMMAND MODE USER TYPES 'mhx'
POWER-UP SEQUENCE Figure 5A. S0=1, S119=1
(factory default) DATA MODE
(ATA or ATO Com mand) Escape Sequence DTR or COMMAND MODE POWER-UP SEQUENCE Figure 5B. S0=1, S119=0 500 msec DATA MODE mand) A or ATO Com Escape Sequence DTR or
(AT COMMAND MODE POWER-UP SEQUENCE Figure 5C. S0=0 500 msec The escape sequence will not be accepted unless both the MHX-920 and the terminal are set to the same baud rate The terminal must be set for 9600 baud 8N1 in order for the modem to accept these characters. If mhx is typed incorrectly, the modem will immediately enter into data mode. If the five seconds elapses without any response from the user, the modem will go into data mode. In command mode, the module autobauds, meaning that it will adapt to the baud rate of the DTE equipment to which it is connected. Therefore, when in command mode, you may change the baud rate of your equipment, and the MHX-920 will automatically adjust to this baud rate once an AT string is issued. The new baud rate is stored in register S102. Several baud rates ranging from 2400 to 115200 may be selected. You can place the modem into Data Mode from Command Mode either by:
Issuing the answer command (ATA <ENTER>); or, Issuing the online command (ATO <ENTER>). The modem will now attempt to communicate with other MHX-920 modules. While in Data Mode, the modem will communicate through the serial port at the same baud rate as was last used in Command Mode2. To return to Command Mode, you can either:
Send the escape sequence. (The escape sequence consists of 1 second of inactivity, followed by the characters +++ followed by another second of inactivity.); or, Toggle the DTR line (depending on the &D parameter see pg 11). The escape sequence must be issued at the baud rate that the modem has been set to. If the modem is set to 19200 baud, and the escape sequence is issued at 9600 baud, for example, the modem will not recognize it, and will not go into Command Mode. Figure 5 provides a state diagram for power-up, command mode, and data mode. Note that there are three different variants of the state diagram which depend on the values of registers S0 and S119. See the appropriate sections for more details about these registers. The factory defaults are S0=1 and S119=1. 2 It is possible to enter into Data Mode at a different baud rate from what is currently being used in Command Mode by issuing the command ATS102=x, where x is one of the valid baud rates. Care must be taken when setting the baud rate in this manner. If you issue another AT string after attempting to set the baud rate using ATS102 <ENTER>, the modem will again autobaud and automatically revert to the baud rate of the host equipment. For example, if your equipment is running at 9600 baud and you wish to set up the modem to run at 19200 baud, the following command line entry would be suitable:
ATS102=5&WA <ENTER>
The first part (S102=5) sets the baud rate to 19200. The next characters
(&W) write this baud rate to memory. The last character (A) puts the modem into Data Mode. Once in Data Mode, the modem is unable to autobaud, and is fixed at 19200 baud. By combining several commands into one command line entry, and then immediately putting the modem online, the modem is not given a chance to autobaud back to 9600. 14 MHX-920 Operating Manual: Chapter 3 Modes of Operation 4. Configuration This chapter provides a detailed description of the various operating parameters of the MHX-920. Section 4.1 provides a quick-start approach which outlines the minimum requirements for establishing communication between two MHX-920 modules. The settings will not necessarily provide optimal performance for your application, but will verify that the modules are functioning correctly. Section 4.2 describes the AT Command interface, and the various AT Commands. Section 4.3 covers all S-Register parameters which affect the operation of the modem, and Section 4.4 provides a description of all diagnostic features of the modem. 4.1 Quick Start Approach There are several parameters that must be set in order to establish communication between a pair of MHX-920 modules. The MHX-920 is equipped with four standard factory default settings. Instead of manually configuring each individual operating parameter, a global command may be used to quickly configure the modem for a particular type of operation. For example, to quickly implement Network 1, Factory default 1 would be applied to the Master, and Factory default 2 would be applied to the Slave. To quickly set up Network 2, apply Factory 1 to the Master, Factory 3 to the Repeater, and Factory 4 to the Slave. These defaults will get you started and only ensure that a link can be established, but do not necessarily provide the best performance. the communications link is discussed in later sections. Optimization of To implement the basic network illustrated in Figure 6, Network 1, 1. Insert the module into the development board socket with the antenna connector towards the edge of the board. 2. Attach the supplied antenna. 3. Connect a straight through serial cable between the DB9 connector and the serial port on your PC 4. Run any terminal application program such as Hyperterminal and set the terminal applications serial port settings to 9600 baud, 8N1 5. Apply power to the development board 6. While the three RSSI LEDs are blinking, type mhx (you have about 5 seconds to do this). The modem should respond with OK. 7. Configure the unit to Factory Setting 1 by typing AT&F1 <return>. This puts the unit into Master Point-to-point mode. 8. Store these settings to memory by typing AT&W <return>. 9. Put the modem into Data Mode by typing ATA (or ATO) <return>
10. Perform above steps for the second unit, using Factory Setting 2 instead of Factory Setting 1. This will configure the second unit as a Slave. Warning: After testing the units for correct operation using the quick-start approach, be sure to modify some of the security parameters such as Network Address and Encryption Key, to avoid unintentional communication with other users of MHX-920 products.. M Network 1 S M M Network 2 R R S S Figure 6. Basic Networks MHX-920 Operating Manual: Chapter 4 Configuration 15 The units should now be communicating. Remember, the parameters defined by Factory Settings 1 and 2 will likely not be the most ideal for your application, but will quickly allow you to test the units. A complete summary of the settings defined by all four factory settings can be found in Appendix C. Factory Default Settings. Settings are not immediately stored in non-volatile memory, therefore, the command &W is issued to store the current configuration into non-volatile memory. Settings are retained even after powering down. All user selectable parameters for the MHX-920 are described in detail in Sections 4.2 and 4.3:
Checking the Link To check if the units are communicating, observe the LED indicators on the development board which houses the Slave unit. If the link is good, up to three RSSI LEDs on the Slave modem should be active along with the RX/Sync LED, and if the link is absent (due to a fault at one end or another, such as misconfiguration), the LEDs will be in either scanning mode or inactive. See Section 2.2 for complete LED operation. Characters typed at the Master terminal should appear at the Slaves terminal, and vice versa. Also, verify that the RX LED blinks as packets of data are received at the Master modem. As data is sent from Slave to Master, the RX indicator should blink on as correct packets of data are received. At this point, the Masters RSSI LEDs should become active. It is recommended that if the MHX-920 will be deployed in the field where large distances separate the units, the modems should be configured and tested in close proximity (e.g., in the same room) first to ensure a good link can be established and settings are correct. This will facilitate troubleshooting, should problems arise. 4.2 AT Commands Several AT Commands are supported by the MHX-920. These commands affect the operation of the modem in command mode and the transition between data and command modes. More commands and S-Register settings are discussed in Sections 4.3 and 4.4. To make the command line more readable, you can insert as many spaces as desired. The command line holds up to 16 characters, not including the AT prefix. If you want to send more than one command line, wait for a response before entering the AT prefix at the start of the next command line. To re-execute the previous command, enter A/. The modem will execute the previous command line. When in Command Mode, the modem autobauds, meaning that it will automatically adjust to the baud rate of the terminal. You may change the terminal baud rate while in Command Mode without losing communication with the modem. For the AT command protocol, an escape sequence consists of three consecutive escape codes preceded and followed by at least 1 second of inactivity. Typically, the + character is used as the escape code.
+++
preceded and followed by 1 second of inactivity The escape sequence will not be accepted unless both the MHX-920 and the terminal are set to the same baud rate 16 MHX-920 Operating Manual: Chapter 4 Configuration Note that the terminal must be configured to the same baud rate as the modem in order for the modem to recognize the escape sequence. The modem is unable to autobaud while in Data Mode. The following is a description of all available commands. * denotes standard factory settings. All of the following commands must be preceded by AT. A Answer The A command puts the modem into data mode, where the modem attempts to communicate with other compatibly configured modems (Type ATA
<return>). E Command Echo Your modem is preset to return (or echo) commands to the host microprocessor when in Command Mode. E0
*E1 No Command Echo Command Echo I Identification The I command returns various modem information settings. I0=
I1 I2 I3 I4 I5 I6 I7 String up to 16 characters stored in non-volatile memory Product Code (MHX-920) Issue ROM Check (OK or ERROR) Product Identification (Firmware Version) Firmware Date Firmware Copyright Firmware Time Serial Number O On-line Mode The O command puts the modem into data mode. This command is identical to the A command. Q Quiet Mode Your modem is preset to send responses when it executes commands, and there after to keep the host informed of its status.
*Q0 Q1 Enable modem responses Disable modem responses V Result Codes display Your modem can either display result codes as words or numbers. V0
*V1 Display Result Codes as numbers Display Result Codes as words MHX-920 Operating Manual: Chapter 4 Configuration 17 W Connection Result This parameter determines the modem response at the transition from Data Mode to Command Mode
*W0 W1 W2 Reports computer (DTE) baud rate as CONNECT xxxx Reports wireless rate between modems as CARRIER xxxx. Reports modem (DCE) baud rate as CONNECT xxxx Z Reset and load stored configuration The Z command resets the modem and loads the stored configuration.
&C DCD (Data Carrier Detect) The &C command controls the modems DCD output signal to the host microprocessor. This command determines when the DCD is active.
&C0
*&C1 DCD on when modems are synchronized. DCD is always DCD is always ON
&C2 on when unit is configured as Master. DCD used for output data framing and Modbus mode. See page 33 for details.
&D DTR (Data Terminal Ready) The &D command controls what action the modem performs when the DTR input line is toggled. The DTR input is controlled by the host microprocessor.
*&D0 DTR line is ignored
&D1
&D2
&D3 Not Supported DTR disconnects and switches to Command Mode DTR disconnects and resets modem. Modem will remain in this state until DTR again goes active.
&F Load Factory Default Configuration Refer to Appendix A (page 19) for a summary of the modem commands
&F1 Master
&F2 Slave
&F1 Master
&F3 Repeater
&F4 Slave The &F command resets the modem and loads the default factory configuration.
&F1 Master Point-to-Multipoint. Designed to communicate
&F2
&F3
&F4 with modems configured as &F2 or &F3. Slave. Designed to communicate with another modem configured as &F1. Repeater. Designed to communicate with modems configured as &F1 and &F4. Slave working with factory default Repeater and factory default Master. Communicates directly with Repeater configured as &F3.
&K Handshaking The &K command controls the handshaking between the modem and host microprocessor.
&K0
&K2
*&K3 Enable hardware handshaking (RTS/CTS) Disable handshaking RTS/CTS input data framing. See page 33 for details. 18 MHX-920 Operating Manual: Chapter 4 Configuration
&S DSR (Data Set Ready) The &S command controls the DSR line for the modem, and determines when it is active DSR is always ON DTR/DSR signaling. With &S2, Slaves and repeaters
&S0
*&S1 DSR is ON in Data Mode, OFF in Command Mode
&S2 output the state of the masters DTR on their local DSR line. Master outputs the state of a slaves DTR on its local DSR line only in point-to-point mode (i.e., DTR is a two-way signal transfer in point-
to-point mode, and a one-way signal transfer in point-to-multipoint mode).
&V View Configuration The &V command displays all S registers and their current values.
&E Framing Error Check This command enables or disables Framing Error Check. When enabled, the modem looks for the stop bit. If the stop bit is absent, the byte is thrown out. When enabled, the modem also does a parity check. Note that the data format (number of data bits, parity type, and number of stop bits) is defined by S register 110.
*&E0 Disable Framing Error Check
&E1 Enable Framing Error Check
&W Write Configuration to Memory The &W command stores the active configuration into the modems non-
volatile memory. Sxxx? Read S register value This command causes the modem to display the current setting of S register xxx. Sxxx=yyy Set S register value (see section 4.3 S-Registers) This command sets the specified S register to a value specified by yyy. Configuration options are not stored in non-volatile memory until the WRITE command (&W) is executed MHX-920 Operating Manual: Chapter 4 Configuration 19 AT Command Result Codes The MHX-920 module can display the results of a command as either text strings or numerical data. The following chart shows resulting text string and corresponding numeric result. 0 3 4 7 8 9 10 12 13 14 15 17 18 33 62 64 OK NO CARRIER ERROR CONNECT 2400 CONNECT 3600 CONNECT 4800 CONNECT 7200 CONNECT 9600 CONNECT 14400 CONNECT 19200 CONNECT 28800 CONNECT 38400 CONNECT 57600 CONNECT 115200 CARRIER 45000 CARRIER 20000 20 MHX-920 Operating Manual: Chapter 4 Configuration Refer to Appendix A (page 45) for a summary of the S-Registers. S Registers 2 through 5 cannot be stored to non-
volatile memory. 4.3 S Registers The S Registers described in this section affect the operating characteristics of the modem. S Register 0 - Auto Answer If this register is set to zero, the modem will power up in command mode. If this register is set to one, the modem will power up in data mode. S Register 2 - Escape Code This register contains the ASCII value of the escape character. The default value (decimal 43) is equivalent to the ASCII character +. Values greater than 127 disable the escape feature and prevent you from returning to the Command Mode. This register cannot be stored to non-
volatile memory. If the modem is reset, or powered down, the default value is restored. Default is + (decimal 43). S Register 3 - CR Control Code This register contains the ASCII value of the carriage return character. This is the character that is used to end the command line and is also the character that appears after the modem sends a response. This register cannot be stored to non-volatile memory. If the modem is reset, or powered down, the default value is restored. Default is CR (decimal 13). S Register 4 - Linefeed Control Code Register S4 sets the ASCII value of the linefeed character. The modem sends the linefeed character after sending a carriage return character when sending text responses. This register cannot be stored to non-
volatile memory. If the modem is reset, or powered down, the default value is restored. Default is LF (decimal 10). S Register 5 - Backspace Control Code Register S5 sets the ASCII value of the backspace character. This character is both the character created by entering BACKSPACE and the character echoed to move the cursor to the left. This register cannot be stored to non-volatile memory. If the modem is reset, or powered down, the default value is restored. Default is BS (decimal 8). MHX-920 Operating Manual: Chapter 4 Configuration 21 Only one Master can exist for each network. Master Point to Multipoint Master Point to Point Slave Repeater Master - Diagnostics (see Section 4.4) S Register 101 - Operating Mode The Operating Mode (register S101) partly defines the personality of the MHX-920 module. Allowable settings for this register are 1 through 5 as follows:. S101=1 S101=2 S101=3 S101=4 S101=5 The default for this register depends on which factory default is selected as shown below:
Default for Factory Setting &F1 is 1 (Master Point-to-Multipoint) Default for Factory Setting &F2 is 3 (Slave) Default for Factory Setting &F3 is 4 (Repeater) Default for Factory Setting &F4 is 3 (Slave) 1)Master - Point to Multipoint. In any given network, there is always only one Master. All other units should be configured as either Slaves or Repeaters. When defined as a Point-to-Multipoint Master, the modem broadcasts data to all Slaves and Repeaters in the network, and is also the ultimate destination for data transmitted by all Slaves and Repeaters. In addition, the Master defines the following network parameters to be utilized by all other modems in the network (See the appropriate sections for a complete description of these parameters):
n Maximum Packet Size (S112) n Minimum Packet Size (S111) n Wireless Link Rate (S103) n Hop Interval (S109) 2)Master - Point to Point. This mode of operation is identical to Master Point-to-Multipoint, with the exception that the Master only broadcasts to one particular Slave or Repeater. The modem with which communication occurs is defined by the Unit Address (S105). For example, if a Slave has been assigned Unit Address 100, and the Master wishes to communicate with that Slave, the Master must also be assigned a Unit Address of 100. If there are Repeaters in the network, they will pass the packet through to the Slave, and vice versa. Because Repeaters also have Slave functionality (i.e., a Repeater can be connected to a terminal), the Master can choose to communicate solely with a Repeater. This would be accomplished by assigning the same Unit Address to both the Master and the Repeater. 22 MHX-920 Operating Manual: Chapter 4 Configuration 3)Slave. Up to 65535 Slaves may exist in a network, all of which communicate with the common Master (either directly or via Repeater(s)). Slaves cannot directly communicate with other. Slaves only provide acknowledgement for packets of data sent by the Master when the Master is in Point-to-Point mode. In multipoint mode, multiple slaves would conflict with one another if they were all trying to acknowledge the Master at the same time. The Master does, however, send acknowledgements to all messages it receives from Slaves. The Master initiates communications by sending a broadcast message to all Slaves. All Slaves are free to respond in a Slotted ALOHA fashion, meaning that each Slave can choose one of several windows in which to transmit. If there happens to be two Slaves attempting to talk at the same time, the Master may not receive the data, and the Slaves therefore would not get an acknowledgement. At this point, the Slaves would attempt to get the information through at random time intervals, thus attempting to avoid any more conflicts. Special parameters which control the Slaves response characteristics can be modified with S Registers S115 and S213. 4) Repeater. A more precise title would be Repeater/Slave, because a Repeater also has much of the same functionality as a Slave. A terminal can be connected at the Repeater location and communicate with the Master terminal. There is no restriction to the number of Repeaters in a network, allowing for communication over virtually limitless distances. The presence of one Repeater in a network automatically degrades system throughput by half. Additional Repeaters, regardless of the quantity, do not diminish system throughput any further. To understand Repeater operation, consider the module as belonging to two hopping patterns at the same time: The Primary Hopping Pattern and the Secondary Hopping Pattern. In Figure 7, the Master belongs to Hopping Pattern 1, and communicates with the Repeater on this hopping pattern. The Slave belongs to Hopping Pattern 2, and communicates with the Repeater on this hopping pattern. The whole system belongs to Network 50 (i.e., all units must be assigned the same Network Address (S104), which in this case was selected to be 50. Note that Slaves and Master only communicate on their respective Primary Hopping Pattern. Repeaters communicate on the Primary Hopping Pattern when communicating with the Master (or with another Repeater between itself and the Master). Repeaters communicate on their Secondary Hopping Pattern when communicating with Slaves (or with another Repeater between itself and the Slaves). Figure 8 shows another example. If the Repeater is not also being used as a Slave (there is no DTE connected to the serial port), it is recommended that the Repeaters baud rate be set to 115K, and that handshaking be disabled (&K0). This will help ensure a smooth flow of data through the network. Network 50 Hop Pattern 2 PHP=1 Master PHP=1 SHP=2 Repeater PHP=2 Slave Hop Pattern 1 Figure 7 - Repeater Operation Hop Pattern 3 Repeater PHP=2 SHP=3 Slave PHP=3 Repeater PHP=1 SHP=2 Master PHP=1 Hop-
Pattern 1 Slave PHP=2 Hop Pattern 2 Figure 8 - A Network Utilizing Three Hopping Patterns If there is no DTE connected to the Repeater, turn off handshaking (&K0) and set the baud rate to 115K. MHX-920 Operating Manual: Chapter 4 Configuration 23 S Register 102 - Serial Baud Rate The Serial Baud Rate is the current speed that the modem is using to communicate with the DTE. In command mode, the module autobauds, meaning that it will adapt to the baud rate of the DTE equipment to which it is connected. Therefore, when in command mode, you may change the baud rate of your equipment, and the MHX-920 will automatically adjust to this baud rate once an AT string is issued. The new baud rate is stored in register S102. If you issue a command to change the value of S102, the instant you issue another command, the baud rate will revert back to that of the DTE equipment. Therefore, it is advisable to operate in Command Mode at the desired baud rate for Data Mode. See page 14 for additional information. The possible values are:
1 2 3 4 5 6
*7 8 9 10 11 115200 57600 38400 28800 19200 14400 9600 7200 4800 3600 2400 It is generally advisable to choose the highest rate that your terminal equipment will handle to maximize performance, unless a limitation on the available bandwidth is desired. If the DTE is a personal computer, the port can usually be used reliably at 115200. Issuing the &Fx command (factory default) does not affect the current setting of S102. S Register 103 - Wireless Link Rate The Wireless Link Rate is the speed and optimization method for which modems will communicate over the RF link. It is only necessary to set this parameter on the Master unit. Units configured as Repeaters and Slaves will ignore this setting, and adjust automatically to the rate of the Master. The allowable settings are:
*2 4 Fast without Forward Error Correction Fast with Forward Error Correction Depending on the application requirements, each mode will provide different throughput and performance. Appendix E. Performance Tables give some indication of the performance to be expected in each mode. In general, Forward Error Correction (FEC) reduces throughput, but in some environments will actually increase throughput. FEC can reduce the number of bad data packets, and hence reduce the need to retransmit. The Master determines the Wireless Link Rate. This setting on all other modems is ignored.. 24 MHX-920 Operating Manual: Chapter 4 Configuration Select a Network Address and assign it to all units which will be included in the network. Warning: Microhard Systems strongly recommends changing the Network Address to a value different than the factory default before deploying the network. Use the same Unit Address on both units for point-to-
point mode. In multipoint mode, set each Slave and Repeater to a different Unit Address. Valid Unit Addresses are 1 to 65535. S Register 104 - Network Address The Network Address defines the membership to which individual units can be a part of. By establishing a network under a common Network Address, the network can be isolated from any other concurrently operating network. As well, the Network Address provides a measure of privacy and security. Only those units which are members of the network will participate in the communications interchange. Valid values for the Network Address range from 0 to 65535, inclusive. To enhance privacy and reliability of communications where multiple networks may operate concurrently in close proximity, it is suggested that an atypical value be chosen perhaps something meaningful yet not easily selected by chance or coincidence. Default is 1. S Register 105 - Unit Address In point-to-point operation, the Unit Address on both the Master and Slave
(or Repeater) units must be the same. In a multipoint system, the Unit Address uniquely identifies each Slave and Repeater from one another. Each unit in a multipoint system must have a unique Unit Address ranging from 1 to 65535. Do not use 0 as a Unit Address, and do not use a Unit Address more than once within the same Network. This is required because the Master must be able to acknowledge each unit individually, based on the Unit Address. S Register 106 - Primary Hopping Pattern S Register 206 - Secondary Hopping Pattern Since the MHX-920 is a frequency-hopping modem, the carrier frequency changes periodically according to one of 64 pseudo-random patterns, defined by the Primary and Secondary Hopping Patterns. Valid entries for each are 0 through 63. Patterns 0 through 61 are pre-programmed, with details provided in Appendix F. Patterns 58 through 63 are user-editable patterns. See Appendix F for details. The concept of Primary and Secondary Hopping Patterns was introduced in the discussion of S Register 101 (Operating Mode). Using the designations M[a,] Rx[a,b] and Sx[a] where:
- M indicates Master;
- R indicates Repeater;
- S indicates Slave;
- x is the Unit Address;
- a is the primary hopping pattern; and,
- b is the secondary hopping pattern;
MHX-920 Operating Manual: Chapter 4 Configuration 25 Master Slave Master Repeater Slave Master Repeater1 Repeater2 Slave the following diagrams illustrate the methodology for deploying simple to complicated networks:
M[1]
M[1]
M[1]
M[1]
S1[1]
R1[1,2]
R1[1,2]
R1[1,2]
S2[2]
R2[2,3]
R2[2,3]
S3[3]
R3[3,4]
S4[4]
It is reasonable to consider a Repeater as being both a Slave and a Master, alternating between Primary and Secondary Hopping Patterns as the unit changes channel. When communicating with the Master, R1 is acting like a Slave on Primary Hopping Pattern 1. When communicating with R2 and S4, R1 is acting like a Master on Secondary Hopping Pattern 2. If multiple Repeaters are used, they should have different Secondary Hopping Patterns:
Consider R1 in the illustration below. R1[1,2]
R2[2,5]
S3[5]
M[1]
S4[2]
Slaves and Masters do not use Secondary Hopping Patterns R5[1,3]
R8[1,4]
R6[3,6]
S7[6]
S9[4]
Remember to assign a unique Unit Address (1 to 65535) to each unit in the system Note that all units have a unique Unit Address. Networks of any complexity can be created by linking multiple Repeaters and Slaves:
R1[1,2]
S2[2]
S3[2]
R5[3,6]
S6[6]
S7[6]
R8[3,7]
R9[7,8]
S10[8]
M[1]
R4[1,3]
S11[1]
S12[1]
With a limitation of 64 hopping patterns, one might suspect that there is a limitation to the number of repeaters in a system. However, if the units are far enough away from one another, hopping patterns may be reused in different sections of the network, without causing interference. 26 MHX-920 Operating Manual: Chapter 4 Configuration All units within a network must use the same encryption key. Warning: Microhard Systems strongly recommends changing the Encryption Key to a value different than the factory default before deploying the network. S Register 107 - Encryption Key The Encryption Key provides a measure of security and privacy of communications by rendering the transmitted data useless without the correct key on the receiver. Valid Encryption Keys range from 0 to 65535. Keep in mind that all units within the network must use the same key for communications to succeed. S Register 108 - Output Power Level The Output Power Level determines at what power the MHX-920 transmits. The MHX-920s sensitive receiver can operate with very low power levels, so it is recommended that the lowest power necessary is used; using excessive power contributes to unnecessary RF pollution. The allowable settings are:
0 1
*2 3 1 mW 10 mW 100 mW 1000 mW Ideally, you should test the communications performance between units starting from a low power level and working upward until the RSSI is sufficiently high and a reliable link is established. Although the conditions will vary widely between applications, typical uses for some of the settings are described below:
Power Use 1 mW For in-building use, typically provides a link up to 300 feet on the same floor or up/down a level. Outdoors, distances of 10 km can be achieved if high-gain (directional) antennas are placed high above ground level and are in direct line-of-sight. 10 mW 200-500 ft indoors, 8-15 km* outdoors. 100 mW 400-800 ft indoors, 15-25 km* outdoors. 1000 mW
(1 W) Typically provides communications up to a distance of 1000 feet or more in-building on the same floor or up/down a few levels, depending on building construction (wood, concrete, steel, etc.). In ideal line-of-sight conditions, up to 30 km* or more can be achieved. Note that only an antenna with a gain of no more than 6 dBi may be used. Any higher is a violation of FCC rules. See IMPORTANT warning below.
* These outdoor distances assume antennas are mounted at least 100 ft above ground level MHX-920 Operating Manual: Chapter 4 Configuration 27 IMPORTANT:
FCC Regulations allow up to 36 dBi effective radiated power (ERP). Therefore, the sum of the transmitted power (in dBm), the cabling loss and the antenna gain cannot exceed 36 dBi. 1 mW = 0 dBm 10 mW = 10 dBm 100 mW = 20 dBm 1000 mW = 30 dBm For example, when transmitting 1 Watt (30 dBm), the antenna gain cannot exceed 36 - 30 = 6 dBi. If an antenna with a gain higher than 6 dBi were to be used, the power setting must be adjusted appropriately. Microhard Systems Inc. limits the MHX-920s transmitted power to 100mW for all units purchased with antennas with gain above 6dBi. S Register 109 - Hopping Interval This option determines the frequency at which the modems change channel. Note that the Master controls this parameter for the entire network. This setting is ignored in units configured as Slaves or Repeaters. The allowable settings are:
1 2 3
*4 5 6 7 8 8 msec 12 msec 16 msec 20 msec 30 msec 45 msec 80 msec 120 msec The hopping interval is controlled by the master. The slave and repeater units will use the hopping interval setting from the master. Warning: Communication will fail if the hopping interval is not set according to the guidelines of Appendix E.;.. repeaters in the system;
Some of the shorter hop intervals are incompatible in combination with:
the value set for link rate (S103); and, larger maximum packet sizes (S112). See Appendix E for optimal Hopping Interval settings in relation to packet size and link rate. 28 MHX-920 Operating Manual: Chapter 4 Configuration S Register 110 - Data Format This register determines the format of the data on the serial port. Allowable settings are:
*1 2 3 4 5 6 7 8 9 10 11 8 bits, No Parity, 1 Stop 8 bits, No Parity, 2 Stop 8 bits, Even Parity, 1 Stop 8 bits, Odd Parity, 1 Stop 7 bits, No Parity, 1 Stop 7 bits, No Parity, 2 Stop 7 bits, Even Parity, 1 Stop 7 bits, Odd Parity, 1 Stop 7 bits, Even Parity, 2 Stop 7 bits, Odd Parity, 2 Stop 9 bits, No Parity, 1 Stop S Register 111 - Packet Minimum Size S Register 112 - Packet Maximum Size S Register 114 - Packet Size Control S Register 116 - Packet Character Timeout These settings determine the conditions under which the modem will transmit accumulated data over the air. S Register 111 - Minimum Size Valid entries for this register are 1 to 255 bytes, which defines the minimum number of bytes to receive from the DTE before encapsulating them in a packet and transmitting over the air. Note that if register S114=0 at any particular Repeater or Slave, that Repeater or Slave will ignore its own S111 register and abide by the Masters S111 setting. If S114=1 at any particular Repeater or Slave, that Repeater or Slave will use its own local S111 setting. The default for S111 is 1 byte. S Register 112 - Maximum Size This setting has a range of 2 to 255, and defines the maximum number of bytes from the DTE which should be encapsulated in a packet. This value should be greater than the minimum packet size, but not smaller than is necessary for reliable communications. If the wireless link is consistently good and solid, a maximum size of 255 will yield the best throughput
(depending on the higher level protocols of the connected equipment). However, if the link is poor (e.g., experiencing excessive interference) and data is frequently retransmitted, the maximum packet size should be reduced. This decreases the probability of errors within packets, and reduces the amount of traffic in the event that retransmissions are required. Note that if register S114=0 at any particular Repeater or Slave, that Repeater or Slave will ignore its own S112 register and abide by the Masters S112 setting. If S114=1 at any particular Repeater or Slave, that Repeater or Slave will use its own local S112 setting. The default for S112 is 255 bytes. When S114=0, the Minimum and Maximum Packet Size is controlled by the Master , therefore, the Slave and Repeater units will use the Minimum and Maximum Packet Size setting from the Master. When S114=1, Slave and Repeater units will use their local S111 and S112 settings for packet size control in point-to-point mode MHX-920 Operating Manual: Chapter 4 Configuration 29 S Register 114 - Packet Size Control This register, when set to 1, allows for Repeater and Slaves local S111 and S112 to override those of the Master when the system is operating in point-
to-point mode. This may be useful for controlled asymmetrical data flow. The master always transmits in the first portion of the hop interval, with slaves and repeaters responding back to the master on the second portion of the hop interval. Setting the masters max packet size smaller than that of the slave would ensure that the master uses less of the available time within the hop interval for transmitting data, thereby allocating more time for the slave. S Register 116 - Packet Character Timeout This register has valid entries of 0 to 254 milliseconds. The Packet Character Timeout timer looks for gaps in the data being received from the DTE. The timer is only activated after the Minimum Packet Size has been accumulated in the modem. After which, if the timer detects a gap in the data exceeding the Packet Character Timeout value, the modem will transmit the data. The MHX-920 will accumulate data in its buffers from the DTE until one of the following requirements is met (whichever occurs first):
The Maximum Packet Size (in bytes) has been accumulated;
The Minimum Packet Size has been accumulated AND the Packet Character Timeout interval has elapsed. The default for the Packet Character Timeout is 8 ms. If set to 0 ms, the unit will buffer exactly the minimum packet size before transmitting. S Register 113 - Packet Retransmissions This register applies to both Master and Repeater operation. It does not apply to Slave operation. In point-to-multipoint mode, the Master will retransmit each data packet exactly the number of times defined by the Packet Retransmissions parameter. In point-to-point mode, the Master will only retransmit the packet if it does not get an acknowledgement from the slave with which it is communicating. In this case, the Master will continue to retransmit until an acknowledgement is received, or the retransmission limit is reached. When the retransmission limit is reached, the Master discards the packet. The Master retransmits once at the beginning of each hopping interval until the limit is reached. This parameter is not necessary in Slave units since all Slaves receive acknowledgement from the Master, and neednt blindly retransmit if it has knowledge that the Master has received the packet.. As discussed previously, the Repeater effectively behaves as both a Master and a Slave. When the Repeater is tuned to its Secondary Hopping Pattern (acting as a Master), the Packet Retransmissions Parameter comes into play. The Repeater will re-send packets of data on to Slaves or other Repeaters exactly the number of times defined by the Packet Retransmissions parameter. Recipients of the packet will discard any duplicates The valid settings for this parameter are 0 to 255 retransmissions. The default is 1. 30 MHX-920 Operating Manual: Chapter 4 Configuration S Register 213 - Packet Retry Limit Packet Retry Limit is analogous to Packet Retransmissions, but specifically applies to Slaves and Repeaters. This parameter is not used by the Master. Because the Slave has the advantage of receiving acknowledgements from the Master, it is not necessary to blindly retransmit each packet. If the Slave does not get an acknowledgement on the next hop, it will retransmit its packet. This will continue until the Packet Retry Limit is reached or an acknowledgement is received. If the limit is reached, the modem will give up and discard the data. Valid settings are 0 to 255 retries. The default value is 2. The Repeater makes use of this parameter when it is tuned to its Primary Hopping Pattern and is acting like a Slave. S Register 115 - Packet Repeat Interval A parameter that is specific to Slaves and Repeaters is the Packet Repeat Interval. The allowable settings are 1 through 255. The default is 1. This parameter defines a range of random numbers that the Slave will use as the next slot in which it will attempt to send the packet. For example, if this register is set to 7, the Slave will choose a number between one and seven as the next slot in which to transmit. Suppose the random number generator picks 5, then the Slave will transmit in the fifth time slot. A Slave will transmit a maximum of once per hopping interval, however, depending on the duration of the hopping interval and the maximum packet size, more than one slot per hop is potentially available. The Slave will transmit more frequently when a Repeat Interval with a smaller range is selected. Choose 1 to have the Slave transmit in the first available slot. Choose higher intervals for less frequent transmission, or to avoid collisions between many Slaves in the system. This register is always disregarded and taken as S115=1 in Point-to-Point mode. MHX-920 Operating Manual: Chapter 4 Configuration 31 S Register 117 - Modbus Mode Modbus Mode allows for the MHX-920 to be fully Modbus compatible. For Modbus operation, the general requirement is to get the packet of data to the receiving serial port with no gaps in the data. The MHX-920 incorporates a Modbus Mode which implements a delay at the receiving modem to ensure that no gaps are introduced. For most applications, the following settings are suitable for Modbus operation:
1. Set Modbus Mode parameter S117 = 1 2. 3. 4. Set the minimum packet size (S111) to 1 byte Set the character timeout S116 (rounded to the nearest ms) to roughly 2.5 byte lengths. For example, at 9600 baud, Rounded up, S116 = 3ms S116 = 1/9600 x 10 x 2.5 x 1000 = 2.6ms Set parameter S121 = 3 byte lengths. For example, at 19200 baud S121 = 1/19200 x 10 x 3 x 1000 = 1.56ms. Rounded up, S121 = 2ms 5. Set S120 as follows:
Slave Side S120 = (Hop Interval in ms) x (1 + # of Master retransmissions) x (1 +
# of Repeaters over 1) eg. Master Side S120 = (Hop Interval in ms) x (1 + # of Repeaters over 1) Hop Interval S109=4 (20 ms), Master Retransmissions S113=1 Number of Repeaters in system = 2; then, S120 = 20 x (1 + 1) x (1 + 1) = 80 ms 6. Try to set the hop interval as short as possible while still ensuring adequate throughput. It is recommended to set the Hop Interval and Maximum Packet Size as specified in Appendix E. Performance Tables. For example, for Master to Slave communication with no FEC, If a throughput of 60kbps is required, set the Hop Interval S109=3, and set the Maximum Packet Size S112=110. The allowable settings for this register are:
*0 1 Disabled Enabled 32 MHX-920 Operating Manual: Chapter 4 Configuration S Register 118 - Roaming This mode is activated on slaves and repeaters by setting register S118=1. In this mode, a slave/repeater looks for synchronization with a Master having the same network address and encryption key, but without regard for the hopping pattern S106. Once the slave/repeater finds such a master, it tunes to that masters hopping pattern. If synchronization is lost, the slave/repeater will again begin searching for a new master. Using this algorithm, a mobile unit can roam and automatically synchronize with a new master once it loses communication with the previous one. It is essential that all Masters with which a roaming slave/repeater will be communicating with use a hopping pattern from within the same group. See Appendix F. The allowable settings for this register are:
*0 1 Disabled Enabled S Register 119 - Quick Enter to Command By setting this register to 1, a delay of 5 seconds is introduced at power-up before the modem goes into data mode. If, during these 5 seconds, the user enters mhx the modem will instead go into Command Mode, and reply with OK. The terminal baud rate must be set to 9600 baud. If an incorrect character is entered, the modem will immediately go into Data Mode. The default setting is 1 - Enabled. S Register 120 - RTS/DCD Framing S Register 121 - DCD Timeout The MHX-920 supports two special types of data framing:
Output (or DCD) Data Framing Input Data Framing is enabled by configuring the Handshaking Parameter as
&K2. This type of framing makes use of the S120 parameter as illustrated in Figure 9. Parameter S120 can be set to any value between 0 and 254 ms. Input (or RTS/CTS) Data Framing; and, RTS CTS TXD Data going into MHX-910 S120 (ms) 0 to 1 ms Figure 9 - Input Data Framing MHX-920 Operating Manual: Chapter 4 Configuration 33 To enable output (DCD) data framing, set the Data Carrier Detect parameter as &C2. This type of framing uses both S120 and S121 registers as shown in Figure 10. Valid ranges for each parameter are 0 to 254 ms DCD RXD Data leaving MHX-910 S120 (ms) S121 (ms) Figure 10 - Output Data Framing S Register 122 - Remote Control This register either disables or enables remote control at a repeater or slave unit. When disabled, a slave/repeaters settings may be remotely read by the master, but may not be remotely modified. the slave/repeater allows the network master full remote control access. See Section 4.4.3 for details. The default is 0 - disabled. When enabled, S Register 123 - RSSI Reading This register displays the average signal strength in dBm over the previous four hop intervals. The value in this register is also reflected in status lines RSSI1,2 and 3. See Section 2.2 for a description of RSSI, and how it is derived. 34 MHX-920 Operating Manual: Chapter 4 Configuration 4.4 Diagnostics, Statistics and Remote Control The MHX-920 provides several commands which are very useful for troubleshooting and analyzing the performance of the radio system. 4.4.1 Spectrum Analyzer Feature (ATG) Issuing the command ATG <return>,causes the MHX-920 to perform a sweep of the entire operating spectrum, giving a signal strength read-out in dBm for each channel as shown below:
Noise level, '*'- mean value, '.'- max value ch 1 -138dBm *
ch 2 -139dBm *
ch 3 -139dBm *
ch 4 -139dBm *
ch 5 -139dBm *
ch 6 -139dBm *
ch 7 -130dBm *
ch 8 -116dBm *
ch 9 -135dBm *
... ch 127 -135dBm *
Paging -135dBm *
Channel 1 is at frequency 902.4 MHz, with all subsequent channels in 200 kHz increments. This feature also displays average received signal strength for 12 channels above the 902-928 MHz ISM band. This area of the spectrum is used by paging networks. When deploying a network, the spectrum analyzer feature is useful for determining which parts of the ISM band may be noisy. This knowledge can be used to select an appropriate hopping pattern, or for creating a custom hopping pattern which avoids those frequencies. In addition, the presence of extremely high paging noise (> -25dBm) may indicate a need to install Microhards external cavity filter in line with the antenna. See Chapter 5 for details. 4.4.2 Statistics (ATP) The ATP <return> command provides a list of several statistics as follows:
# of data packets sent = 0
# of data packets received = 0
# of Slave's retries = 0
# of Slave's packets dropped = 0
# of Slave's sync errors = 0
# of CRC errors = 0 OK The MHX-920 starts the statistics count at zero each time the unit is powered up, or after the ATP command has been issued. By entering the ATP command, all statistics are cleared back to zero. The maximum limit for each statistic is 65535. MHX-920 Operating Manual: Chapter 4 Configuration 35 4.4.3 Remote Control and Diagnostics (S101=5) This is a very powerful tool which allows user to remotely configure and interrogate all units in a multipoint system from the Master unit. Simply by having knowledge of the unit address of each slave/repeater in the system, users can set the unit address of the master to match that of the slave/repeater of interest, set S101=5, go online, and interrogate/modify virtually all parameters of the remote repeater/slave unit. It should be noted that when the master goes online, all other units belonging to the network will synchronize with the master, but only the unit whose unit address matches the masters will respond to the masters diagnostic commands. In addition, in diagnostics mode, the master can change its unit address on-
the-fly, avoiding the delays of going into command mode, modifying the unit address, going back online and re-synchronizing with the entire network, before interrogating a new slave/repeater. The masters unit address can be changed while still maintaining synchronization with the entire network, allowing for quick and efficient diagnostic sessions with all remote units. Ensure that register S122=1 on any slave/repeater that you wish to remotely modify. Table 4 provides a diagnostics command summary. The first column is a list of commands that may be issued at the master. The second column is the corresponding remote register. In general, any command issued without any additional parameters is a read command. For example, if you type:
0 <return>
The remote slave/repeater will send back the value if its S101 register. On the Master terminal screen, you would see:
0 (this is the 0 that you typed, echoed back locally) 3 (this indicates that the remotes S101=3) If you type:
04 <return>
This command would change the remotes operating mode to S101=4
(repeater). The remote unit should return OK. Remember, if the remotes S122=0 (remote control disabled), the remote will respond with ERROR. In Table 4, Column 1, the meanings of the format is as follows:
COMMAND COMMAND(x) A command without (x) indicates that you may not add any additional parameters. i.e., you may only read back the value of the remotes register. You may not modify that register. The only exception to this is the WRITE command e. Type e to force the write command (&W) at the remote modem. Indicates this command may be sent with or without a parameter. Issuing this command without a parameter reads the corresponding remotes register. Issuing this command with the additional parameter x changes the corresponding remotes register to x. Remember, any changes you wish to retain in the event of a powerdown or reset should be stored to non-volatile memory by issuing the write command e. 36 MHX-920 Operating Manual: Chapter 4 Configuration Table 4 - Remote Control and Diagnostics Command Remote Register Description 0(x) 1(x) 2(x) 3(x) 4(x) 5(x) 6(x) 7(x) 8(x) 9(x) a a1 a2 a3 b(x) c(x) d(x) e f g(x) h(x) I(x) j(x) k1 k2 k3 k4 k5 k6 k255 l(x) m(x) n(x) o(x) p(x) S101 S102 S108 S110 S115 S116 S120 S121 S117 S213 test string test string test string test string
&E
&C
&K
&W S123 S104 S106 S206 S113 statistics statistics statistics statistics statistics statistics statistics S119 S118 S114 S111 S112 Operating Mode Baud Rate Output Power Data Format Repeat Interval Character Timeout RTS/DCD Framing DCD Timeout Modbus Mode Retry Limit Read back 'OK' from remote Read back 'Microhard Systems, Inc.' from remote Read back 64 character test string from remote Read back 255 character test string from remote Framing DCD Handshaking Write RSSI Network Address Hopping Pattern Secondary Hopping Pattern Retransmissions Read # of data packets sent Read # of data packets received Read # of Slave's retries Read # of Slave's packets dropped Read # of Slave's sync errors Read # of CRC errors Clear statistics Quick Enter to Command Mode Roaming Packet Size Control Min Packet Size Max Packet Size MHX-920 Operating Manual: Chapter 4 Configuration 37 As mentioned previously in this section, there are some settings that can be changed to the masters own registers while in diagnostics mode. The most useful is the unit address. By changing the masters unit address to that of another slave in the network while in diagnostics mode, users can quickly interrogate/modify many different slaves settings without the delays associated with switching between command and data modes. The commands which apply to the masters own registers are shown in Table 5. Table 5 - Master Diagnostics Commands Command r(x) s t(x) u(x) v(x) Master Register Description Unit Address back to normal operating mode Hopping Interval Network Address Hopping Pattern S105 S101 S109 S104 S106 38 MHX-920 Operating Manual: Chapter 4 Configuration The installation, removal or maintenance of all antenna components must be carried out by qualified and experienced personnel. 5. Installation The installation, removal or maintenance of all antenna components must be carried out by qualified and experienced personel. The MHX-920 complies with FCC part 15 at the modular level for operation in the license-free 902-928 MHz ISM band. This chapter provides guidelines for installing and deploying equipment which incorporates the MHX-920 module. 5.1 Estimating the Gain Margin Successful communication between MHX-920 modules is dependent on three main factors:
System Gain Path Loss Interference System gain is a calculation in dB describing the performance to be expected between a transmitter-receiver pair. The number can be calculated based on knowledge of the equipment being deployed. The following four factors make up a system gain calculation:
1. Transmitter power (user selectable 0, 10, 20 or 30 dBm) 2. Transmitter gain (transmitting antenna gain minus cabling loss between the transmitting antenna and the MHX-920 module) 3. Receiver gain (Receiving antenna gain minus cabling loss between the receiving antenna and the module) 4. Receiver sensitivity (Specified as -105 dBm on the MHX-920 module) In the following illustration, the transmitting antenna has a gain of 6 dB, and the receiving antenna has a gain of 3 dB. The cable loss between the module and the antenna is 2 dB on both the transmitting and receiving side. Cable Loss = 2 dB Cable Loss = 2 dB Antenna Gain = 6 dB Antenna Gain = 3 dB Transmitter 30 dBm Output Power Receiver Sensitivity =
-105 dBm The power level has been set to 30 dBm (1W) on the transmitter, and the receiver sensitivity for the MHX-920 is -105 dBm. System gain would be calculated to be:
30 - 2 + 6 + 3 - 2 + 105 = 140 dB. MHX-920 Operating Manual: Chapter 5 Installation 39
) m
(
t h g i e H e s a B Mobile Height
(m) Distance (km) When deploying your system, care must be taken to ensure the path loss
(reduction of signal strength from transmitter to receiver in dB) between equipment does not exceed the system gain (140 dB in the above example). It is recommended to design for a gain margin of at least 10 dB to ensure reliable communication. Gain margin is the difference between system gain and path loss. Referring to the same example, suppose the path loss is 100 dB, the gain margin would be 40 dB, which is more than adequate for reliable communication. Path loss is a very complicated calculation which mainly depends on the terrain profile, and the height of the antennas off the ground. The following table provides path loss numbers for varying antenna heights and antenna separation: These numbers are real averages taken from rural environments. They do not apply to urban, non-line-of-sight environments. Distance
(km) 5 5 8 8 8 16 16 16 16 16 16 Base Height Mobile Height Path Loss
(m) 15 30 15 15 15 15 15 15 30 30 30
(m) 2.5 2.5 2.5 5 10 2.5 5 10 10 5 2.5
(dB) 116.5 110.9 124.1 117.7 105 135.3 128.9 116.2 109.6 122.4 128.8 Once the equipment is deployed, you can verify the signal strength by entering into Command Mode and reading Register S123. This register provides the average signal strength in dBm. The minimum strength for communication reliable communication, you should try to deploy the equipment such that signal strength exceeds -95 dBm. For consistent
-105 dBm. roughly is 40 MHX-920 Operating Manual: Chapter 5 Installation 5.2 Antennas and Cabling This section describes the recommended procedure for installing cabling and antennas for use with the MHX-920 module. 5.2.1 Internal Cabling The most common method for installing the module is to run a cable from the modules MCX connector to a reverse TNC bulkhead connector on the chassis of the equipment as shown in Figure 11. This cable can be purchased from Microhard Systems. Reverse TNC Connector RG316 Cable with MCX male connector and Reverse TNC bulkhead connector MCX female connector 0 1 9
-
X H M Figure 11. Suggested Internal Cabling Cable losses are negligible for the short piece used within the chassis. Additional losses up to 0.5 dB may be present in the MCX and Reverse TNC connections. MHX-920 Operating Manual: Chapter 5 Installation 41 5.2.2 Installing External Cables, Antennas and Lightning Arrestors The installation, removal or maintenance of all antenna components must be carried out by qualified and experienced personnel. Never work on an antenna system when there is lightning in the area. Direct human contact with the antenna is potentially unhealthy when the MHX-920 is generating RF energy. Always ensure that the MHX-920 equipment is powered down during installation. Surge Arrestors The most effective protection against lightning is to install two lightning
(surge) arrestors. One at the antenna, and the other at the interface with the equipment. The surge arrestor grounding system should be fully interconnected with the transmission tower and power grounding systems to form a single, fully integrated ground circuit. Typically, both ports on surge arrestors are N-female. Cabling The following coax cables are recommended:
The installation, removal or maintenance of all antenna components must be carried out by qualified and experienced personnel. Never work on an antenna system when there is lightning in the area. Direct human contact with the antenna is potentially unhealthy when the MHX-920 is generating RF energy. Always ensure that the MHX-920 equipment is powered down during installation. Cable Loss (dB/100ft) LMR 195 LMR 400 LMR 600 10.7 3.9 2.5 Factors to take into consideration when choosing a cable are:
price;
bend radius limitations (the lower performance cables generally can bend more sharply) performance requirements; and, distance between the equipment and the antenna. When installing the cable, always begin fastening at the top near the antenna connector/surge arrestor. The cable must be supported at the top with a hose clamp or wrap lock, and at 5 ft intervals down the length of the tower. Over-tightening the fasteners will dent the cable and reduce performance. If properly grounded surge arrestors are not installed at both the top and the bottom of the cable, then the cable should be grounded to the tower at these locations using a cable grounding kit. If the tower is non-conductive, then a separate conductor, physically separate from the cable, should be run down the tower. 42 MHX-920 Operating Manual: Chapter 5 Installation To comply with FCC regulations,
.you must limit ERP to 36 dBm or less. Antenna Before choosing an antenna, you should have some knowledge of the path loss and the topology of the equipment. If the equipment is in a fixed location and is to communicate with only one other unit also in a fixed location, then a Yagi antenna is suitable. Choose a Yagi with enough gain to ensure adequate gain margin. When deploying the Yagi, point the antenna towards the intended target, ensuring the antenna elements are perpendicular to the ground. If the equipment must communicate with multiple or mobile transceivers, then select an Omni-directional antenna with appropriate gain. The Effective Radiated Power (ERP) emitted from the antenna cannot exceed +36 dBm ERP. With the MHX-920 set to full power, ERP is calculated as follows:
ERP = 30 - (Cabling and Connector Losses) + (Antenna Gain) < 36 Use the guidelines in the previous section for calculating cable and connector losses. If cabling and connector losses are 2 dB, then the maximum allowable gain of the antenna will be 8 dB. External Filter Although the MHX-920 is capable of filtering out RF noise in most environments, there are circumstances that require external filtering. Paging towers, and cellular base stations in close proximity to the MHX-920 antenna can desensitize the receiver. Microhard Systems external cavity filter eliminates this problem. The filter has two N-female ports and should be connected in line at the interface to the RF equipment. Weatherproofing Type N and RTNC connectors are not weatherproof. All connectors should be taped with rubber splicing tape (weatherproofing tape), and then coated with a sealant. MHX-920 Operating Manual: Chapter 5 Installation 43 44 MHX-920 Operating Manual: Chapter 5 Installation A. Modem Command Summary The following provides a command summary for the MHX-920 module. Factory settings are denoted with a *. AT Commands A E S Registers S0 I O Q V W Z
&C
&D
&F
&K
&S Answer Command Echo E0 No Echo
* E1 Command Echo Identification I0 Custom I1 Product Code I2 ROM Checksum test I3 Firmware Version I4 Firmware Date I5 Copyright I6 Firmware Time I7 Serial Number On-line Mode Quiet Mode
* Q0 Enables Result Codes Q1 Disables Result Codes Result Codes Display V0 Display as Numbers
* V1 Display as Words Connection Result
* W0 Reports DTE as CONNECT xxxx W1 DTE) rate as CARRIER xxxx. W2 Reports DCE as CONNECT xxxx Reset and load stored configuration DCD (Data Carrier Detect)
&C0 DCD is always on
* &C1 DCD is on when modems are synchronized
&C2 DCD used for output data framing DTR (Data Terminal Ready)
&D0 DTR ignored
* &D2 DTR disconnects and switches to command
&D3 DTR disconnects and resets modem Load Factory Default
&F1 Master
&F2 Slave
&F3 Repeater
&F4 Slave through Repeater Handshaking
&K0 Disable Handshaking
&K2 RTS/CTS Input Framing
* &K3 Enable Handshaking DSR (Data Set Ready)
&S0 DSR is always on
* &S1 DSR on in data, off in command mode
&S2 DSR/DTR signaling View Configuration Write configuration to memory Read S register value Set S register value
&V
&W Sxx?
Sxx=yy Result Codes 0 3 4 7 8 9 10 64 OK NO CARRIER ERROR CONNECT 2400 CONNECT 3600 CONNECT 4800 CONNECT 7200 CARRIER 20000 12 13 14 15 17 18 33 62 CONNECT 9600 CONNECT 14400 CONNECT 19200 CONNECT 28800 CONNECT 38400 CONNECT 57600 CONNECT 115200 CARRIER 45000 Auto Answer 0 = power up in Command Mode,
*1 = power up in Data Mode Escape code [0...255] default + (43) CR character [0...255] default <cr> (13) Line Feed [0...255] default <lf> (10) Backspace [0...255] default <bs> (8) Operating Mode 1 - Master Point to Multipoint 2 - Master Point to Point 3 - Slave 4 - Repeater 5 - Master Diagnostics Serial Baud Rate 1 = 115200, 2 = 57600, 3 = 38400 4 = 28800, 5 = 19200, 6 = 14400
*7 = 9600, 8 = 7200, 9 = 4800, 10 = 3600, 11 = 2400 Wireless Link Rate
*2 = Fast w/o FEC 4 = Fast with FEC Network Address [0...65535]
Unit Address [1...65535]
Primary Hopping Pattern [0...63]
Secondary Hopping Pattern [0...63]
Encryption Key [0...65535]
Output Power Level 0 = 1 mW, 1 = 10 mW, *2 = 100 mW, 3 = 1000 mW Hopping Interval 1 = 8 msec, 2 = 12 msec, 3 = 16 msec,
*4 = 20 msec, 5 = 30 msec, 6 = 45 msec, 7 = 80 msec, 8 = 120 msec Data Format
* 1 = 8N1, 2 = 8N2, 3 = 8E1, 4 = 8O1 5 = 7N1, 6 = 7N2, 7 = 7E1, 8 = 7O1 9 = 7E2, 10 = 7O2, 11 = 9N1 Packet Minimum Size [1...Maximum Size]
Packet Maximum Size [2...255]
Packet Retransmissions [0...255]
Packet Retry Limit [0...255]
Packet Size Control
*0=Disabled, 1=Enabled Packet Repeat Interval [1..255]
Default = 1 Packet Character Timeout [0...254 ms]
Modbus Mode
*0 = Disabled, 1 = Enabled Roaming
*0 = Disabled, 1 = Enabled Quick Enter to Command 0 = Disabled, *1 = Enabled RTS/DCD Framing Interval [0...254 ms]
DCD Timeout [0...254 ms]
Remote Control
*0 = Disabled, 1 = Enabled RSSI (dBm) S2 S3 S4 S5 S101 S102 S103 S104 S105 S106 S206 S107 S108 S109 S110 S111 S112 S113 S213 S114 S115 S116 S117 S118 S119 S120 S121 S122 S123 MHX-920 Operating Manual: Appendix A Modem Command Summary 45 46 MHX-920 Operating Manual: Appendix A Modem Command Summary B. Serial Interface The MHX-920 module uses 8 pins on the header connector for asynchronous serial I/O. The interface conforms to standard RS-232 signals without level shifting, so direct connection to a host microprocessor is possible. The signals in the asynchronous serial interface are described below:
RX DCD Data Carrier Detect - Output from Modem - When asserted (TTL low), DCD informs the DTE that a communications link has been established with another MHX-920. Receive Data - Output from Modem - Signals transferred from the MHX-
920 are received by the DTE via RX. Transmit Data - Input to Modem - Signals are transmitted from the DTE via TX to the MHX-920. TX DTR Data Terminal Ready - Input to Modem - Asserted (TTL low) by the DTE to SG inform the modem that it is alive and ready for communications. Signal Ground - Provides a ground reference for all signals transmitted by both DTE and DCE. DSR Data Set Ready - Output from Modem - Asserted (TTL low) by the DCE to inform the DTE that it is alive and ready for communications. DSR is the modems equivalent of the DTR signal. RTS Request to Send - Input to Modem - A handshaking signal which is asserted by the DTE (TTL low) when it is ready. When hardware handshaking is used, the RTS signal indicates to the DCE that the host can receive data. CTS Clear to Send - Output from Modem - A handshaking signal which is asserted by the DCE (TTL low) when it has enabled communications and transmission from the DTE can commence. When hardware handshaking is used, the CTS signal indicates to the host that the DCE can receive data. Notes:
It is typical to refer to RX and TX from the perspective of the DTE. This should be kept in mind when looking at signals relative to the modem (DCE); the modem transmits data on the RX line, and receives on TX. DCE and modem are often synonymous since a modem is typically a DCE device. DTE is, in most applications, a device such as a host microprocessor. Modem
(DCE) 1 2 3 4 5 6 7 8 Signal DCD RX TX DTR SG DSR RTS CTS Host Microprocessor
(DTE) IN IN OUT OUT IN IN OUT IN Arrows denote the direction that
(e.g., DCD signals are asserted originates at the DCE and tells the DTE that a carrier is present). MHX-920 Operating Manual: Appendix B Serial Interface 47
48 MHX-920 Operating Manual: Appendix B Serial Interface C. Sample Schematic Diagram The following is a sample microprocessor implementation with a MICROCHIP PIC 16C74 and the MHX-920. The MHX-920 performs no level shifting on the serial port, so direct connection to the host microprocessor is possible. DO NOT CONNECT THE MHX-920 TO RS 232 DRIVER OUTPUTS. DAMAGE TO THE UNIT MAY RESULT. On this implementation, the onboard SCI of the PIC 16C74 is directly connected pins 2 and 3 of the MHX-920. The bi-
directional Port D is used for asserting or monitoring control signals from the MHX-920. The RESET signal is a momentary active low signal asserted by the host microprocessor. RESET initializes the MHX-920 and places the system in a known state. This signal should be set high after the host microprocessor has been reset. PIC16C74 MHX-920 RC7 RC6 RD0 RD1 RD2 RD3 RD4 RD5 RD6 RXD TXD DCD DTR DSR RTS CTS 2 3 1 4 6 7 8 RESET 31 Power Connections not shown MHX-920 Operating Manual: Appendix C Sample Schematic Diagram 49 50 MHX-920 Operating Manual: Appendix C Sample Schematic Diagram D. Factory Default Settings AT&F1 - Master Default Settings E1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8 AT&F3 - Repeater Default Settings E1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8 DCD DTR Framing Handshaking DSR Operating Mode Serial Baud Rate Wireless Link Rate Network Address Unit Address Primary Hop Pattern Encryption Key Output Power Hop Interval Data Format Packet Minimum Size Packet Maximum Size Packet Retransmissions Packet Size Control Packet Repeat Interval Character Timeout (ms) Modbus Mode Roaming Quick Enter to Command RTS/DCD Framing (ms) DCD Timeout (ms) Remote Control Secondary Hop Pattern Packet Retry Limit
&C1 (On)
&D0 (DTR is ignored)
&E0 (Disabled)
&K3 (Enabled)
&S1 (On in Data, Off in Command) S101=1 (Master P-MP) S102=7 (9600 baud) S103=2 (Fast, No FEC) S104=1 S105=1 S106=0 S107=1 S108=2 (100mW) S109=4 S110=1 (8N1) S111=1 S112=43 S113=1 S114=0 S115=1 (Dont Care) S116=8 S117=0 S118=0 S119=1 S120=0 S121=0 S122=0 S206=2 (Dont Care) S213=2 (Dont Care) DCD DTR Framing Handshaking DSR Operating Mode Serial Baud Rate Wireless Link Rate Network Address Unit Address Primary Hop Pattern Encryption Key Output Power Hop Interval Data Format Packet Minimum Size Packet Maximum Size Packet Retransmissions Packet Size Control Packet Repeat Interval Character Timeout (ms) Modbus Mode Roaming Quick Enter to Command RTS/DCD Framing (ms) DCD Timeout (ms) Remote Control Secondary Hop Pattern Packet Retry Limit
&C1 (On)
&D0 (DTR is ignored)
&E0 (Disabled)
&K3 (Enabled)
&S1 (On in Data, Off in Command) S101=4 (Repeater) S102=7 (9600 baud) S103=2 (Fast, No FEC) (Set by Master) S104=1 S105=3 S106=0 S107=1 S108=2 (100mW) S109=4 (Set by Master) S110=1 (8N1) S111=1 S112=43 S113=1 S114=0 S115=1 S116=8 S117=0 S118=0 S119=1 S120=0 S121=0 S122=0 S206=2 S213=2 AT&F2 - Slave Default Settings E1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8 AT&F4 -Slave Through Repeater Default Settings E1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8 DCD DTR Framing Handshaking DSR Operating Mode Serial Baud Rate Wireless Link Rate Network Address Unit Address Primary Hop Pattern Encryption Key Output Power Hop Interval Data Format Packet Minimum Size Packet Maximum Size Packet Retransmissions Packet Size Control Packet Repeat Interval Character Timeout (ms) Modbus Mode Roaming Quick Enter to Command RTS/DCD Framing (ms) DCD Timeout (ms) Remote Control Secondary Hop Pattern Packet Retry Limit
&C1 (On)
&D0 (DTR is ignored)
&E0 (Disabled)
&K3 (Enabled)
&S1 (On in Data, Off in Command) S101=3 (Slave) S102=7 (9600 baud) S103=2 (Fast, No FEC) (Set by Master) S104=1 S105=2 S106=0 S107=1 S108=2 (100mW) S109=4 (Set by Master) S110=1 (8N1) S111=1 S112=43 S113=1 (Dont Care) S114=0 S115=1 S116=8 S117=0 S118=0 S119=1 S120=0 S121=0 S122=0 S206=2 (Dont Care) S213=2 DCD DTR Framing Handshaking DSR Operating Mode Serial Baud Rate Wireless Link Rate Network Address Unit Address Primary Hop Pattern Encryption Key Output Power Hop Interval Data Format Packet Minimum Size Packet Maximum Size Packet Retransmissions Packet Size Control Packet Repeat Interval Character Timeout (ms) Modbus Mode Roaming Quick Enter to Command RTS/DCD Framing (ms) DCD Timeout (ms) Remote Control Secondary Hop Pattern Packet Retry Limit
&C1 (On)
&D0 (DTR is ignored)
&E0 (Disabled)
&K3 (Enabled)
&S1 (On in Data, Off in Command) S101=3 (Slave) S102=7 (9600 baud) S103=2 (Fast, No FEC) (Set by Master) S104=1 S105=4 S106=2 S107=1 S108=2 (100mW) S109=4 (Set by Master) S110=1 (8N1) S111=1 S112=43 S113=1 (Dont Care) S114=0 S115=1 S116=8 S117=0 S118=0 S119=1 S120=0 S121=0 S122=0 S206=2 (Dont Care) S213=2 MHX-920 Operating Manual: Appendix D. Factory Default Settings 51 52 MHX-920 Operating Manual: Appendix D Factory Default Settings E. Performance Tables The scope of this appendix is to find the best possible performance and maximum packet size at different modes of operation. The setup assumes a baud rate of 115k, no retries and no retransmissions. WARNING: Communication will fail if the maximum packet size (S112) exceeds the recommended optimal packet size. . Slave <--> Master Communication.
(No Repeater) Link Rate S103=2 Slave <--> Master Communication.
(No Repeater) Link Rate S103=4 Repeater <-->
Master Direct Communication. Link Rate S103=2 Repeater <-->
Master Direct Communication. Link Rate S103=4 Slave <--> Master Through One or More Repeaters. Link Rate S103=2 Slave <--> Master Through One or More Repeaters. Link Rate S103=4 Hop Interval 1 (8 ms) 2 (12 ms) 3 (16 ms) 4 (20 ms) 5 (30 ms) 6 (45 ms) 7 (80 ms) 8 (120 ms) 1 (8 ms) 2 (12 ms) 3 (16 ms) 4 (20 ms) 5 (30 ms) 6 (45 ms) 7 (80 ms) 8 (120 ms) 1 (8 ms) 2 (12 ms) 3 (16 ms) 4 (20 ms) 5 (30 ms) 6 (45 ms) 7 (80 ms) 8 (120 ms) 1 (8 ms) 2 (12 ms) 3 (16 ms) 4 (20 ms) 5 (30 ms) 6 (45 ms) 7 (80 ms) 8 (120 ms) 1 (8 ms) 2 (12 ms) 3 (16 ms) 4 (20 ms) 5 (30 ms) 6 (45 ms) 7 (80 ms) 8 (120 ms) 1 (8 ms) 2 (12 ms) 3 (16 ms) 4 (20 ms) 5 (30 ms) 6 (45 ms) 7 (80 ms) 8 (120 ms) Optimal Packet Size (bytes) Throughput
(kbps)*
14 66 110 154 255 255 255 255 5 34 54 76 130 210 255 255 N/A 3 22 44 101 178 255 255 N/A N/A 5 16 43 80 174 255 N/A 3 22 43 93 174 255 255 N/A N/A N/A 14 40 80 174 255 20 52 66 74 83 56 31 21 4 22 28 32 38 43 30 20 N/A 1 13 21 32 39 31 21 N/A N/A 2 6 12 16 20 20 N/A 1 13 21 31 38 31 21 N/A N/A N/A 6 12 16 19 20 MHX-920 Operating Manual: Appendix E. Performance Tables 53 54 MHX-920 Operating Manual: Appendix E. Performance Tables F. Hopping Patterns This Appendix provides a guide for selecting appropriate hopping patterns (S106,S206). There are 64 hopping patterns: The first 62 come pre-programmed from the factory as per the table below. There are 31 patterns in Group A and 31 in Group B. When deploying a network, it is recommended that you use choose hopping patterns all belonging to the same group. Patterns have been designed to notch out certain segments of the ISM band. Pattern Number Spectrum Used 0, 2, 4, 6, 8, 10, 12 902.4 - 927.6 MHz 14, 16, 18, 20 22, 24, 26, 28 905.2 - 924.8 MHz 908.0 - 927.6 MHz Group A Patterns 0,2,4...60 30, 32, 34, 36 902.4 - 907.2, 913.2 - 927.6 MHz 38, 40, 42, 44 46, 48, 50, 52 54, 56, 58, 60 902.4 - 912.4, 918.4 - 927.6 MHz 902.4 - 917.4, 923.6 - 927.6 MHz 902.4 - 922.0 MHz 1, 3, 5, 7, 9, 11, 13 902.6 - 927.4 MHz 15, 17, 19, 21 23, 25, 27, 29 905.4 - 925.0 MHz 907.8 - 927.4 MHz Group B Patterns 1,3,5...61 31, 33, 35, 37 902.6 - 907.4, 913.0 - 927.4 MHz 39, 41, 43, 45 47, 49, 51, 53 55, 57, 59, 61 902.6 - 912.6, 918.2 - 927.4 MHz 902.6 - 917.8, 923.4 - 927.4 MHz 902.6 - 922.2 MHz Patterns 58 to 63 -may be manually entered or edited by entering AT&H at the Command Line, and following the prompts. Each pattern must use a channel only once, and must consist of exactly 50 channels. There are 127 channels available ranging from Channel 1 at 902.4 MHz up to Channel 127 at 927.6 MHz. MHX-920 Operating Manual: Appendix F. Hopping Patterns 55 56 MHX-920 Operating Manual: Appendix F. Hopping Patterns G. Technical Specifications Data Interface Signals Bandwidth / Data Rate Electrical/Physical Asynchronous Serial Port, TTL Levels Sig. Gnd, TX, RX, DCD, DSR, DTR, RTS, CTS 2,400 - 115,200 bps, uncompressed half-duplex, Approx. 85 kbps sustained in intelligent asymmetrical full-duplex Communications Range1 Power Requirements transmission mode 30 kilometres (19 miles) 5 VDC, 1.0 Amp Power Consumption 600 mA max, 300 mA typical at 1W transmit; 200 mA receive Operating Frequency 902-928 MHz System Gain Sensitivity Output Power Spreading Code Hopping Patterns Error Detection Error Correction Adjacent Channel Rejection In-band Rejection Out-of-band Rejection Dimensions (LxWxH) 135 dB
-105 dBm 1, 10, 100, 1000mW (user-selectable) Frequency Hopping 64 pseudo-random, user-selectable CRC-16 with auto re-transmit User-selectable Forward Error Correction (FEC)
> 60 dB
> 70 dB
> 80 dB Encl: 3.5 x 2.1 x 1. (90 mm x 53 mm x 25 mm) Weight 75 grams Operating Environment Temperature: -40 to +70C Humidity: 5 to 95%, non-condensing Storage Temperature
-40 to 90C 1. Clear line-of-sight, elevated high-gain antennas. MHX-920 Operating Manual: Appendix G. Technical Specifications 57 58 MHX-920 Operating Manual: Appendix H. Mechanical Drawings 1 f o 1 t e e h S B N
:
y B n w a r D 2 0
-
2 4 0 1 D
:
r e b m u N t n e m u c o D A e z i S 0 0 0 2
, 4 1 y l u J
, y a d i r F H. Mechanical Drawing
. v e R 2 0 0 8 5 7 2 0 0 2 0 0 9 1 5 2 2 0 0 1 0 5 4 0 7 1 0 4 1 2 0 0 5 3 0 0 1 2 0 5 7 0 0 6 0 9
. a i d w e i V p o T 1 n i P 0 2 5 2 1
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. c n I s m e t s y S d r a h o r c i M
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s a e r a d e d a h S MHX-920 Operating Manual: Appendix H. Mechanical Drawing 59 60 MHX-920 Operating Manual: Appendix H. Mechanical Drawings Terminology Used in the MHX-920 Operating Manual I. Glossary Asynchronous communications A method of telecommunications in which units of single bytes of data are sent separately and at an arbitrary time
(not periodically or referenced to a clock). Bytes are padded with start and stop bits to distinguish each as a unit for the receiving end, which need not be synchronized with the sending terminal. Attenuation The loss of signal power through equipment, lines/cables, or other transmission devices. Measured in decibels (dB). Bandwidth The information-carrying capacity of a data transmission medium or device, usually expressed in bits/second (bps). Baud Unit of signaling speed equivalent to the number of discrete conditions or events per second. If each signal event represents only one bit condition, then baud rate equals bits per second (bps) this is generally true of the serial data port, so baud and bps have been used interchangeably in this manual when referring to the serial port; this is not always the case during the DCE-to-DCE communications, where a number of modulation techniques are used to increase the bps rate over the baud rate. Bit The smallest unit of information in a binary represented by either a 1 or 0. system, Abbreviated b. Bits per second (b/s or bps) A measure of data transmission rate in serial communications. Also see baud. Byte A group of bits, generally 8 bits in length. A byte typically represents a character of data. Abbreviated B. Characters per second (cps) A measure of data transmission rate for common exchanges of data. A character is usually represented by 10 bits: an 8-
bit byte plus two additional bits for marking the start and stop. Thus, in most cases (but not always), cps is related to bits per second (bps) by a 1:10 ratio. CRC (Cyclic Redundancy Check) An error-detection scheme for transmitted data. Performed by using a polynomial algorithm on data, and appending a checksum to the end of the packet. At the receiving end, a similar algorithm is performed and checked against the transmitted checksum. Crossover cable (Also known as rollover, null-
modem, or modem-eliminator cable) A cable which allows direct DTE-to-DTE connection without intermediate DCEs typically used to bridge the two communicating devices. Can also be used to make cabled DCE-to-DCE connections. The name is derived from crossing or rolling several lines, including the TX and RX lines so that transmitted data from one DTE is received on the RX pin of the other DTE and vice-versa. to connection Data Communications Equipment (DCE, also referred as Data Circuit-Terminating Equipment, Data Set) A device which facilitates a between Data communications Terminal Equipment (DTEs). Often, two or more compatible DCE devices are used to bridge DTEs which need to exchange data. A DCE performs and conversion of data sent/received by the DTE, and transmits/receives data with another DCE. Common example is a modem. encoding, decoding, signal Data Terminal Equipment (DTE) An end-
device which sends/receives data to/from a DCE, often providing a user-interface for information exchange. Common examples are computers, terminals, and printers. dBm Stands for Decibels referenced to one milliwatt (1 mW). A standard unit of power level commonly used in RF and communications work. n dBm is equal to 10(n/10) milliwatt, so 0dBm = 1mW, -10dBm = 0.1mW, -20dBm =
0.01mW, etc. DCE See Data Communications Equipment. DTE See Data Terminal Equipment. Flow Control A method of moderating the transmission of data so that all devices within the communications link (DTEs and DCEs) transmit and receive only as much data as they can handle at once. This prevents devices from sending data which cannot be received at the other end due to conditions such as a full buffer or hardware not in a ready state. This is ideally handled by hardware using flow-control and handshaking signals, but MHX-920 Operating Manual: Appendix I. Glossary 61 many newer devices use a compact 9-pin connector with only the essential signaling lines used in asynchronous serial communications. Lines have two possible states: high (on, active, asserted, carrying +3 to +25 V) or low (off, inactive, disasserted, carrying -3 to -25 V). RTU (Remote Terminal Unit) A common term describing a DTE device which is part of a wide-
area network. Often a RTU performs data I/O and transmits the data to a centralized station. Serial communications A common mode of data transmission whereby character bits are sent sequentially, one at a time, using the same signaling parallel communications where all bits of a byte are transmitted at once, usually requiring a signal line for each bit. Contrast with line. Shielded cable Interface medium which is internally shrouded by a protective sheath to minimize external electromagnetic interference
(noise). Slave A station which is controlled and/or polled by the Master station for communications. Typically represents one end of a point-to-point connection, or one of the terminal nodes in a point-to-
multipoint network. Often a RTU is linked by a Slave DCE. Spread spectrum A method of transmitting a signal over a wider bandwidth (using several frequencies) than the minimum necessary for the originally narrowband signal. A number of techniques are used to achieve spread spectrum telecommunications, including frequency hopping. Spread spectrum provides the possibility of sharing the same band amongst many users while increasing the tolerance to interference and noise, and enhancing privacy of communications. Throughput A measure of the rate of data trans-
mission passing through a data communication system, often expressed as bits or characters per second (bps or cps). can be controlled also by software using X-ON/X-
OFF (transmitter on/off) commands. Frequency-hopping A type of spread spectrum communication whereby the carrier frequency used between transmitter and receiver changes repeatedly in a synchronized fashion according to a specified algorithm or table. This minimizes unauthorized and interception of telecommunications.
(interference) jamming Full-duplex Where data can be transmitted, bi-
independently, and simultaneously directionally. Half duplex Exists when the communications medium supports bi-directional transmission, but data can only travel in one direction at the same time. Handshaking A flow-control procedure for establishing communications whereby data devices indicate that data is to be sent and await appropriate signals that allow them to proceed. Line-of-sight Condition in which a transmitted signal can reach its destination by travelling a straight path, without being absorbed and/or bounced by objects in its path. Master The station which controls and/or polls one or more Slave stations in a point-to-point or point-
to-multipoint network. Often functions as a server or hub for the network. Non-volatile memory Memory which retains information which is written to it. Null modem cable See Crossover cable. Point-to-point A simple communications network in which only two DTEs are participants. Point-to-multipoint A communications network in which a Master DTE communicates with two or more Slave DTEs. Repeater A device which automatically amplifies or restores signals to compensate for distortion and/or attenuation prior to retransmission. A repeater is typically used to extend the distance for which data can be reliably transmitted using a particular medium or communications device. RS-232
(Recommended Standard 232; more accurately, RS-232C or EIA/TIA-232E) Defined by the EIA, a widely known standard electrical and physical interface for linking DCEs and DTEs for serial data communications. Traditionally specifies a 25-pin D-sub connector, although 62 MHX-920 Operating Manual: Appendix I . Glossary
This product uses the FCC Data API but is not endorsed or certified by the FCC