Eia-232; Basic Protocol - Comtech EF Data LCS-4 Installation And Operation Manual

LCS-4 L-Band Combiner Switch
Remote Control Operation
RS-485 (Full-duplex) summary:
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A.1.2 EIA-232
This is much simpler configuration in which the controller device is connected directly to
the target via a two-wire-plus-ground connection. Controller-to-target is carried, tot eh
target via a two-wire-plus-ground connection. Controller-to-target 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.
A.2 B P
ASIC ROTOCOL
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 8-N-1, exclusively with the baud rate set at
19,200 baud.
All data is transmitted in framed packets. The master is assumed to be a PC or ASCII
dumb terminal, which is controlling the process of monitor and control. The controller is
the only device that is permitted to initiate 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 Li characters are considered printable.
All messages from controller to target require a response (with one exception). This will
either be to return data that 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
Two differential pairs – one pair for controller to target, one pair for target to
controller.
Controller-to-target pair has one line driver (controller), and all targets have
line–receivers.
Target-to-controller pair has one line receiver (controller), and all targets have
tri-state drivers
A-2
Revision 1
MN/LCS4.IOM