General Dynamics CG-1220, Operation And Maintenance Manual

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Appendix C– DTR Remote M&C Protocol CG-6073 (Rev R, June, 2012)
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6.0 RS-485 PROTOCOL FOR DTR MULTI-DROP BUS
For M&C systems that need to communicate over RS-485, there are additional requirements and
restrictions in the DTR M&C protocol. The M&C is the only shell offered on the RS-485 bus. The
command line format is different since multiple devices can be present on the multi-drop RS-485
bus. Since the bus is half duplex and is shared, the set of M&C menu items and keywords is
restricted to those items that do not require interactive (full duplex) features, and do not hold the
bus for longer than is necessary or desirable. Multiple DTR units can be monitored and controlled
on the same bus, as well as equipment whose protocol can co-exist with the RS-485 protocol
format described here.
Message Format
Format of multi-drop serial bus shell messages is:
<stx> <direction> <addr> <text> <etx>
<stx>
is the ASCII start of text (
$02
) character
<direction>
is
$5
on commands sent to the DTR.
<direction>
is
$4
on replies sent from
the DTR.
<addr>
is the address of the device to whom this message is sent
<text>
is the body of the command or response (may be null if there is no response)
<etx>
is the ASCII end of text (
$03
) character
Note:
<stx>
is Ctrl-B
<etx>
is Ctrl-C
<$4>
is Ctrl-D
<$5>
is Ctrl-E
Examples:
To send a "/ 0" to unit with address of 1.
<stx><$5>1/ 0<etx>
Response would be something like:
<stx><$4>0 2000.000<etx>
To send a "WHO" to unit with address of 1.
<stx><$5>1WHO<etx>
Response would be:
<stx><$4>0<cr>3 (3 in control)<etx>
To change frequency of unit 1 (already at /):
<stx><$5><$D>10 = 1999.8<etx>
Response would be:
<stx><$4>0<etx>
To send a "/ 0" to unit with address of 4.
<stx><$5>4/ 0<etx>
Response would be something like:
<stx><$4>0 2000.000<etx>
Note: The first '0' in the response is the master address.