Jenn-Air 1300, 1892 User Manual
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
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 ............................................7
3.2 Handshaking Operation During Transmit and Receive .........7
3.3 Data Transfer Modes .....................................8
3.4 RS232 Data Handling ....................................8
3.5 Receive-to-Transmit Turnround ............................8
4 LIST OF COMMANDS: ........................................10
4.1 Command Mode ........................................10
4.1.1 Activation of the Command Mode: .....................10
4.1.2 Ending of Command Mode ..........................11
4.2 Command Syntax ......................................11
4.3 Baud Rate (AT B0) ......................................12
4.4 Parity (ATB1) ..........................................12
4.5 Format Mode (AT F) .....................................13
4.6 Engineering Test Modes (AT In) ...........................14
4.7 Software Version Information (AT I9) .......................15
4.8 Command Mode Guard Time (AT S154) .....................15
4.9 Centre Radio Frequency (AT S155) ........................15
4.10 Received Signal Strength Indication (RSSI) (AT S156) ........16
4.11 Radio Channel (AT S157) ................................17
4.12 Data Quality (AT S158) ..................................17
4.13 Squelch (AT S159) ......................................18
4.14 Transmission Power (AT S160) ...........................19
4.15 Channel Step Size (AT S161) .............................20
4.16 Test Message Period (AT S162) ...........................20
4.17 Over-Air Symbol Rate (AT S163) ..........................21
4.18 Preamble Period (AT S165) ...............................21
4.19 Frame Synch Tolerance (AT S166) .........................22
4.20 Invert Symbol (AT S167) .................................22
4.21 Squelch Delay (AT S168) .................................23
4.22 Enable/Disable Receive Output Data (AT &D) ...............23
4.23 Enable/Disable Input Echo Data (AT &E) ...................23
4.24 Radio Frequency (AT &F) ................................24
4.25 Save parameters (AT &W) ................................24
4.26 Restore defaults (AT &Y8) ...............................24
4.27 Display parameters (ATT?) ...............................25
4.28 Code Loader (AT S2000) .................................26
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 ....................................32
6.3 Vibration Specifications: .................................32
6.4 Type Approvals ........................................32
LIST OF FIGURES
Figure 1 Timing Information ..........................................9
Figure 2 Front View of Casting ......................................31
Figure 3 Rear View of Casting .......................................31
Figure 4 3U Enclosure .............................................31
LIST OF TABLES
Table 1 Data Connections ...........................................5
Table 2 Power Connections ..........................................6
Table 3 Timing Data ................................................9
Table 4 RSSI Levels ...............................................16
Table 6 Squelch Levels ............................................18
Table 7 Power Levels for G-MAX Radios ...............................19
Table 8 Power Levels for SXn50 Radios ...............................19
Hermes Operator Note Page 3 of 32
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 in a 25kHz channel spacing and
9,600 baud in a 12.5kHz channel spacing.
One of the radio transceivers (the G-Max family) used inside the Hermes is
designed for harsh environments and operates over a wide temperature
range and a high vibration environment.
The standard Hermes is fitted with the SXn50 range of transceivers. This
family has products at VHF, UHF and 868MHz, with a maximum transmit
power of 500mW.
Hermes Operator Note Page 4 of 32
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/min levels are:
DTR Vin Min. (off state) = -15V
DTR Vin Max. (off state) = +2.5V
DTR Vin Min (on state) = +5V
DTR Vin Max (on state) = +15V
DTR Iin Max(on state) = 4mA
5 Signal Ground
6 DSR RS232 level output
Set (+ve) after power is applied to the modem or when the DTE
(host processor) sets DTR +ve. The output is active when the
modem is ready to receive data. The time taken for the output to
become active is <50ms from when DSR or power is applied to
the modem.
7 RTS RS232 level input
The RTS input must be set (+ve) for both data and configuration.
Data is ignored when RTS is clear (-ve).
8 CTS RS232 level output
Set (+ve) if the transmit RS232 data into the modem can be
accepted and the RTS input is set, it is cleared (-ve) otherwise.
Clearing of this signal indicates that the input transmit buffer is
nearly full .The RS232 data must be stopped within 10 bytes of
this signal being cleared. After this point the data is ignored. The
CTS signal is set again if there is room for more than 10 bytes.
9 n/c
Table 1 Data Connections
Hermes Operator Note Page 5 of 32
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 at 1000mW RF output, 24VDC input
(reverse voltage protection with re-settable "polyfuse")
5 Power Supply Ground (isolated from enclosure)
6 I2C Bus Clock (engineering use only)
7 0V (chassis of enclosure)
8 I2C Bus Data (engineering use only)
9 Power Supply Ground (isolated from enclosure)
Table 2 Power Connections
2.3 RF Connector
The RF connection to the modem is a female TNC bulkhead connector.
2.4 Front Panel Indications
There are 3 LED indicators which show the operation of the unit as follows:
P Green Power On when DC supply input present and DTR input
S Orange Status Flashes orange when the transceiver is switched
is high (> 3V)
to transmit or receive. Continuous orange if the
transceiver goes “Out Of Lock” (OOL) which
happens on failure, or when an invalid frequency
is programmed into it.
T Red TX On when the transmitter is turned on.
These LEDs are next to the connectors on both types of enclosure.
Hermes Operator Note Page 6 of 32
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)
are stripped off the input data stream and the data stored as 8 bits only.
The transmission is ended when the input buffer is empty. After the
transmission is complete and the transmitter turned off, the modem
switches back to receive mode. Transmission has priority over reception so
the user has to check by means of the CD handshake line if the radio
channel is free before inputting data.
The timing of the power, handshaking and data transfer is shown in Figure 1
for the G-MAX radio (running at 9600 baud over-air in a 12.5kHz channel)
and for the SXn50 series of radios (running at 19,200 baud over-air in a
25kHz channel).
3.2 Handshaking Operation During Transmit and Receive
The DTE must set the RTS input for the modem to accept data. The RTS
input can be set continuously if no hardware handshake lines are available
on the DTE. The CTS line must be monitored for data packets greater than
256 bytes to ensure that input buffer overflow does not occur. If the data
input is not stopped within 10 characters from the point of buffer overflow,
the input data will be discarded.
Handshaking is also required during the code loading.
The modem starts transmitting when the data is input, regardless of the
state of the CD output. The DTE must check the CD output prior to data
transmission. When the CD output is set this indicates that a RF signal is
present at the antenna. This output is only active when the modem is not
transmitting.
Hermes Operator Note Page 7 of 32
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 because only the 8
data bits of the input character of 11 bits are transmitted. To ensure that no
data is lost at the output, and for the modem to transmit the data in one
continuous packet it is essential that the input and output data rates are set
to at least 2 x the over-air-baud rate. The default over-air baud rate for this
modem working in a 12.5kHz channel is 9600 baud. For this set the input
and output RS232 data rates to 19,200. For a 25kHz channel, with an overair baud rate of 19,200, set the data rates to 38,400 baud.
Some applications running under the Windows™ operating system output
the data with gaps between single or groups of characters. In some cases
this can reduce the character rate below the over-air data rate. When this
occurs, the system will assume that the input data has finished and will turn
the transmitter off when the input data buffer is empty.
If more characters are input to the modem while the transmitter is being
turned off, the transmit process will re-start. This will appear as bursts of
RF close together. At the receive end, the timing of the data will change as
there will be gaps in the received data stream.
This mode of operation ensures that small data packets are transmitted in
as short a time as possible to reduce the on-air time to a minimum.
3.5 Receive-to-Transmit Turnround
After the last character of a packet of data is output from the receiver, the
receive system is still processing the “end-of-packet” data. This takes ~5ms
when in non-FEC mode and ~10ms in FEC mode. During this period the
processor does not accept any input data. The figures apply for default
settings: 19,200 baud rate and 4800 symbol/sec over-air baud rate
Hermes Operator Note Page 8 of 32
Figure 1 Timing Information
Time (ms)
Function Description
G-MAX
(9600 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
Data input to Data output (FEC mode) <75 <55
Table 3 Timing Data
SXn50
(19200 baud)
Hermes Operator Note Page 9 of 32
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:
<wait>+++<wait> <CR><LF>
Where <wait> 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<CR><LF>
The modem is now ready to be configured. Transmitting or reception is
blocked during Command Mode.
If the "+++" string is input without a <CR><LF> then the string is transmitted
as normal data. Note that one or more consecutive “+” characters in the
input data are held in the modem until it is determined that it is not a “+++”
string.
The configuration mode is only accepted if the RTS line is set. The “+++”
string is only accepted if this string is the first three characters and there has
been no data for greater than the time set by register S154.
The +++ string is only transmitted over the air if embedded in a data string as
described above.
Important: any configuration changes made are only saved to the
non-volatile memory after a write command (AT &W).
Note that the communication parameters (baudrate etc) are the programmed
parameters.
Hermes Operator Note Page 10 of 32
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