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CDM-Qx Satellite Modem Revision 5
EDMAC Channel MN/CDMQx.IOM
7–3
Now, a unit that has been designated an EDMAC master not only responds to its own
unique bus address, but it will also be configured to listen for the address, which
corresponds to its EDMAC Slave. When a complete message packet has been received by
the EDMAC Master, it will begin to transmit this packet over the satellite channel, using
the overhead bytes, which become available.
Note: The ‘normal’ protocol for the message packet is not used over the satellite path, as
it is subject to errors. For this reason, a much more robust protocol is used which
incorporates extensive error checking.
At the distant-end, the EDMAC slave, configured for the correct address, receives these
bytes, and when a complete packet has been received, it will take the action requested,
and then send the appropriate response to the EDMAC Master, using the return overhead
path on the satellite link. The EDMAC Master assembles the complete packet, and
transmits the response back to the M&C Computer.
Apart from the round-trip satellite delay, the M&C Computer does not see any difference
between local and distant-end units - it sends out a packet, addressed to a particular unit,
and gets back a response. It can be seen that the EDMAC Master simply acts as
forwarding service, in a manner, which is completely transparent.
7.3 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, defines 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, defines the unit as
SLAVE, then enter the bus address. The orange EDMAC Mode LED 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 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.
NOTE: EDMAC modes are fully compatible with AUPC modes.