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CDM-Qx Satellite Modem
Remote Control
RS-485 (full duplex) summary:
Two differential pairs - one pair for controller to target, one pair for target to controller.
a. Controller-to-target pair has one line driver (controller), and all targets have line-
b. Target-to-controller pair has one line receiver (controller), and all targets have
C.2
RS-232
This a much simpler configuration in which the controller device is connected directly to
the target via a two-wire-plus-ground connection. Controller-to-target data is carried, via
RS-232 electrical levels, on one conductor, and target-to-controller data is carried in the
other direction on the other conductor.
C.3
Basic Protocol
Whether in RS-232 or RS-485 mode, all data is transmitted as asynchronous serial
characters, suitable for transmission and reception by a UART. In this case, the
asynchronous character format is fixed at 8N1. The baud rate may vary between 1200
and 38,400 baud.
All data is transmitted in framed packets. The controller is assumed to be a PC, which is in
charge of the process of monitor and control. The controller is the only device, which is
permitted to initiate, at will, the transmission of data. Targets are only permitted to transmit
when they have been specifically instructed to do so by the controller.
All bytes within a packet are printable ASCII characters, less than ASCII code 127. In
this context, the Carriage Return and Line Feed characters are considered printable.
All messages from controller to target require a response (with one exception). This will
be either to return data, which has been requested by the controller, or to acknowledge
reception of an instruction to change the configuration of the target. The exception to this
is when the controller broadcasts a message (such as Set time/date) using Address 0,
when the target is set to RS-485 mode.
receivers.
tri-state drivers.
C-2
Revision 6
MN/CDMQx.IOM
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