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SPECIALIST RF DESIGNS
© Copyright Wood & Douglas 2002
Version: 1.3
Issue: July 2002
HERMES RADIO MODEM
OPERATING INSTRUCTIONS
(1892 1300)
LATTICE HOUSE
BAUGHURST
BASINGSTOKE
UK RG26 5LP
Tel: +44 (0) 118 981 1444 Fax: +44 (0) 118 981 1567
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Table Of Contents 1 INTRODUCTION .............................................. 4 2 CONNECTIONS & INDICATIONS ................................. 5 2.1 RS232 Connector ....................................... 5 2.2 Power Connector ........................................ 6 2.3 RF Connector ........................................... 6 2.4 Front Panel Indications ................................... 6 3 MODEM OPERATION .......................................... 7 3.1 Introduction ....................
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5 HARDWARE SPECIFICATION .................................. 28 5.1 Introduction ........................................... 28 5.2 RS232 Port Parameters .................................. 28 5.3 Radio Specifications .................................... 29 6 MECHANICAL SPECIFICATION ................................ 30 6.1.1 Casting Enclosure ................................. 30 6.1.2 3U Rack Mounting Enclosure ......................... 30 6.2 Operating conditions..................................
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1 INTRODUCTION This document describes the operation of the Wood and Douglas Hermes Radio Modem. The Hermes modems provide a transparent data link for a wide range of applications. The internal modem can be used with a range of Wood & Douglas RF products to give great choice in the operating frequency and transmit power. Two enclosure types are available to suit different applications. The Hermes uses 4-Level Frequency Shift Keying (FSK) technology to achieve a RF link data rate of 19,200 baud
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2 CONNECTIONS & INDICATIONS 2.1 RS232 Connector The RS232 connections are made via a 9 way D female with the following connections: Pin No. Function 1 CD Output Set (+ve) when a RF signal above a certain level is present at the RF connector. The threshold is programmable over 10 levels that are defined in section 5.13 2 RXD RS232 data level data output 3 TXD RS232 level data input 4 DTR RS232 level input When set (+ve) by the DTE (host processor) the modem and transceiver is turned on. The max/
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2.2 Power Connector The power and ancillary connections are made via a 9 way D male connector. The power supply input is fully isolated from the chassis of the module. Note: The power supply cannot be used as an RS232 input line. Pin No. Function 1 RSSI Received Signal Strength Output Analogue output proportional to the level of the RF input Level at -110dBm input = ~0.6V and at -60dBm = ~2.1V 2 n/c 3, 4 +ve Supply Input (9 - 36VDC) Receive current <100mA at 24VDC input Transmit current <400mA
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3 MODEM OPERATION 3.1 Introduction The internal modem power supply system is turned on/off with the DTR input. The modem is ready after an initialisation period. The modem enters receive mode using the last set of configuration parameters (RF channel, squelch level etc). The modem starts the transmit sequence after the first data byte is received from the RS232 port. The incoming data is stored while the transmitter is turned on and the preamble output. The start, stop and parity (if 8 bit data
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3.3 Data Transfer Modes In FEC mode every byte of the data, including the "end-of-file" string is scrambled within the modem to ensure that the error correction mechanism operates over non-consecutive bits in the data stream. The frame sync pattern is not scrambled. In non-FEC (High Speed) mode the data is scrambled to minimise problems that could occur with many consecutive 1's or 0's in the input data stream. 3.4 RS232 Data Handling The over-air data rate is faster than the input data rate be
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Figure 1 Timing Information Time (ms) Function Description G-MAX SXn50 (9600 baud) (19200 baud) t1 DTR input-to-modem DSR output <90 <90 t2 RTS input to CTS output <0.5 <0.5 t3 CTS output to Data input >0.1 >0.1 t4 Data input to RF output (non-FEC mode) <25 <25 Data input to RF output (FEC mode) <25 <25 t5 RF output to CD output (at RX end) <5 <2.5 t6 CD output to data output (non-FEC mode) <30 <30 CD output to data output (FEC mode) <50 <45 t7 Data input to Data output (non-FEC mode) <50 <45
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4 LIST OF COMMANDS: 4.1 Command Mode The modem is configurable through the RS232 port. The Command Mode has to be activated to do this, as detailed in the following paragraphs: 4.1.1 Activation of the Command Mode: The Command Mode is activated with the string: +++ Where is a programmable period after transmitting data (which is set by register S154) which has a nominal value of 10ms. The modem responds with: OK The modem is now ready to be configured. Transmi
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4.1.2 Ending of Command Mode The command mode is ended by inputting the string: ATO The modem responds with: OK The modem is now ready for normal modem operation. Note that the communication parameters (baudrate etc) are the programmed parameters. 4.2 Command Syntax 4.2.1 Note: Capital letters MUST be used for all command instructions. 4.2.2 All syntax commands with multiple ‘n’ ‘s accept multiple formats. For example, if ‘nnn’ is specified in the command string, then the follow
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4.3 Baud Rate (AT B0) When the baud rate is changed, the change is made after the Command Mode is ended (with the AT O command). The baud rate is set with the following command: Baud Rate AT B0=n Where: n = 1 4800 n = 2 9600 n = 3 19200 n = 4 38400 Default: n = 3 for 12.5kHz radios n = 4 for 25kHz radios Read: AT B0? Note: this shows the new value, even though the change is not implemented until the Command Mode is exited. Read Return: n Example: AT B0=2 for 96
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4.5 Format Mode (AT F) This command turns the Forward Error Correction (FEC) mode on and off. The over-air format allows for higher speed operation, but with reduced Bit Error Rate (BER) performance with the FEC turned off, or lower speed, improved BER with the FEC turned on. Figure 1 and the associated table give the timing information for both modes of operation. The command is: Format mode AT F=n Where n=0 mode with FEC n=1 high speed mode without FEC Default: n=1 (non-FEC mode) Read
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4.6 Engineering Test Modes (AT In) Format modes: To enable the function AT In=1 To disable the function AT In=0 Modem responds with OK Read status: AT In? Modem responds with m where m=0, not active m=1, active Where n = 2 Output Continuous Preamble (used for checking transmitter and receiver). The preamble is transmitted until stopped by the ATI2=0 or AT I=10 commands, or ending the command mode. Note: for a G-Max, this test must not be run for >10
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4.7 Software Version Information (AT I9) This command tells the modem to output information about the software version. Example: ATI9=1 return software version or ATI9 Return: ‘an ASCII string detailing the ID and versions of the internal processors’ An example of the return data is as follows: Files: Main micro:"QL3z10", Ver.:1.01.05, Date:31/10/2001 Slave micro:"Slave",Ver.:0.00.02, Date:1
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The centre radio frequency of the modem is set as follows: AT S155=nnn.nnnnnn Where: nnn.nnnnnn is the format of the input string for the frequency in MHz Default: current centre frequency. Read: AT S155? Read Return: nnn.nnnnnn Example: AT S155=458.5 sets 458.5MHz AT S155=458.500000 sets 458.5MHz Note that frequencies in multiples of either 12.5kHz or 10kHz only are acceptable. If a whole number of MHz is entered a “.” must be entered before the
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The RSSI level is requested with the command: AT S156? Read Return: nn The data can be added to the end of each received packet as defined in paragraph 5.6. 4.11 Radio Channel (AT S157) The radio transceiver is programmed with a centre frequency (using the AT S155 command). This frequency is set up in the factory at the centre of the RF switching bandwidth. Once programmed with this frequency a Channel Step Size (using AT S161 command) can be programmed. ±99 channels can then
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4.13 Squelch (AT S159) This command sets the squelch threshold to one of 10 pre-set levels as shown in the Table 6. This command enables the user to reduce the chances of local interference showing the channel to be busy which could reduce the occupancy of the system. Squelch Level Level at RF Input ( dBm ±2dB) 1 < -112 2 -110 to -112 3 -108 to -110 4 -105 to -108 5 -103 to -105 6 -101 to -103 7 -99 to -101 8 -97 to -99 9 -95 to -97 10 > -95 Table 6 Squelch Levels The command for setti
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4.14 Transmission Power (AT S160) The command enables the RF transmit power to be modified. Different RF units have different capabilities and may change, depending on what is supplied. The SXn50 range of transceivers have 2 levels only. The levels for the 1W and 2W versions of the G-MAX are shown in Table 7. Table 8 shows the 2 levels for the SXn50 range. Output Power for 1W G-MAX Output Power for 2W G-MAX Power mW dBm Tolerance mW dBm Tolerance Level (nominal) (nominal) (dB) (nominal) (nomi
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The power is set with the command: AT S160=n Where: sets the power threshold <1 to 10> Default: 10 Read AT S160? Read Return: nn Example: AT S160=-10 sets the power level to 10 4.15 Channel Step Size (AT S161) This command sets the channel step size. The basic reference frequency for the radio is either 12.5KHz or 10KHz, giving possible frequency channel steps of 10kHz, 12.5kHz, 20kHz and 25kHz. The Channel Step Size is set with the command: AT S161=n Wh
