Comtech EF Data CDM-570A - Manual (Page 557)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix J Revision 2
J–3
gets back a response. It can be seen that the EDMAC Master simply acts as forwarding service, in
a manner that is completely transparent.
This approach does not require any additional cabling; connection is made using the normal
M&C remote port, which is completely independent from the modem data port. Consequently,
you do not have to worry about configuring the baud rate of the M&C connection to match the
lowest data rate modem in the system. It should be pointed out that, at 2.4 kbps, the effective
throughput of the overhead channel is only 14 asynchronous characters/second. For a message
of 24 bytes, the time between sending a poll request and receiving a response will be around 1.7
seconds. (Note that, when EDMAC-2 or either of the BPSK Turbo rates is in use, the overhead
rate is reduced by a factor of three, and therefore the minimum response time will be around 5
seconds.)
J.3 Setup Summary
To access a distant-end unit:
• Designate a Master/Slave pair: Master at the local-end, Slave at the distant-end.
• On the local-end unit, enable framing and EDMAC, define the unit as MASTER, then enter
the bus address. This is constrained to be ‘base 10' meaning that only addresses such as 10,
20, 30, 40 etc, are allowed.
• Choose a unique bus address for the distant-end. This should normally be set to the ‘base
10' address + 1. For example, if the MASTER unit is set to 30, choose 31 for the distant-end
unit.
• On the distant-end unit, enable framing and EDMAC, define the unit as SLAVE, then enter
the bus address. The orange EDMAC Mode LED on the modem front panel should be
illuminated.
• Set the local-end unit to RS485 remote control, and set the bus address of this local unit.
The orange Remote Mode LED on the modem front panel should be illuminated.
• Once the satellite link has been established, connect the M&C Computer, and begin
communications with both the local and distant end units.
EDMAC modes are fully compatible with AUPC modes.