Chapter 10 Optional Rs422/485 Operation; The Rs422 Standard; The Rs485 Standard - Brainboxes CC-368 User Manual

Chapter 10 Optional RS422/485
Operation

The RS422 Standard.

The RS485 Standard.

PCI Quad 422/485 Card
The RS422 standard defines a serial communications standard. RS422 is a high speed
and/or long distance data transmission. Each signal is carried by a pair of wires and is
thus a differential data transmission system. Over distances up to 40 feet the maximum
data rate is 10 Megabits per second, and for distances up to 4000 feet the maximum data
rate is 100 Kilobytes per second. A 120-Ohm resistor should be used to terminate the
receiving end of the line. It is generally used between one transmitter receiver pair to
ONLY one other transmitter receiver pair, but each output can drive up to 10 receivers.
RS422 Standard
1 Driver up to 10 Receivers
Line Length
40 Feet =
400 Feet = 122m
4000 Feet = 1219m
TTL D
The RS485 standard is similar to the RS422 standard upon which it is based.
The main difference is that up to 32 transmitter receiver pairs may be present on the line
at one time. A 120-Ohm resistor should be used to terminate either end of the main line.
If more than one device may transmit data, the RTS line is used as transmit enable
signal, so preventing contention between talkers.
RS485 Standard
Up to 32 Driver/Receiver Pairs
Line Length
40 Feet =
400 Feet = 122m
4000 Feet = 1219m
R
D
Max Data Rate
12m 10 Mbits/sec
1 Mbits/sec
100 Kbits/sec
Max Data Rate
12m 10 Mbits/sec
1 Mbits/sec
100 Kbits/sec
D R
Chapter 10 Optional RS422/485 Operation x 49
TTL
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