Comtech EF Data CRS-400 - Manual (Page 76)

CRS-400 1:8 Redundancy Switch Revision 0
Remote Control MN/CRS400.IOM
60
In the other direction, on the other pair, each target has a tri-stateable line driver
connected, and the controller has a line-receiver connected. All the line drivers are held in
high-impedance mode until one (and only one) target transmits back to the controller.
Each target has a unique address, and each time the controller transmits, in a framed
‘packet’ of data, the address of the intended recipient target is included. All of the targets
receive the packet, but only one (the intended) will reply. The target enables its output
line driver, and transmits its return data packet back to the controller, in the other
direction, on the physically separate pair.
EIA- 485 (full duplex) summary:
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.
B.3 EIA-232
This is 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 EIA-232 electrical levels, on one conductor, and target-to-controller data is carried in
the other direction on the other conductor.
B.4 B
ASIC
P
ROTOCOL
Whether in EIA-232 or EIA-485 mode, all data is transmitted as asynchronous serial
characters, suitable for transmission and reception by a UART. The asynchronous
character format may be:
8-N-1 8 data bits, no parity, 1 stop bit
7-E-2 7 data bits, even parity, 2 stop bits
7-O-2 8 data bits, odd parity, 2 stop bits.
The selectable baud rates are 300, 1200, 2400, 4800, 9600 and 19,200 baud.