RS422
The Electronics Industry Association (EIA) has developed standards
for data communication. EIA standards where originally marked with the
prefix "RS".
"RS" means that it is a recommended standard, but the standards are now
generally indicated as "EIA" standards.
RS422 was developed for greater distances and higher baud rates than RS232.
It also enables a bus like structure with up to ten receivers, but it is not
a true multi point network there every node could work as transmitter or receiver.
RS422 is a differential voltage loop interface (balanced differential signal);
differential data transmission reduces the effects of ground shifts and induced noise signals.
logical "1" (Mark) is represented by a negative voltage of -3.6V to -6V,
logical "0" (Space) is represented by a positive voltage of +3.6V to +6V,
RS422 can be connected to up to ten receivers,
the data rate is up to 10 Mbps,
cable length could be up to 1.3 km (4000 feet),
the connector is a 37 pin D-Sub connector.
Cat5 cable (shielded twisted pair (STP) or unshielded twisted pair (UTP))
generally exceeds the recommendations for RS-422 and RS-485 systems.
RS422 Connection
(37pin D-Sub) |
Pin |
DESCRIPTION |
1 |
GND |
Shield Ground |
2 |
SRI |
Signal Rate Indicator |
3 |
n/c |
|
4 |
SD |
Send Data |
5 |
ST |
Send Timing |
6 |
RD |
Receive Data |
7 |
RTS |
Request To Send |
8 |
RR |
Receiver Ready |
9 |
CTS |
Clear To Send |
10 |
LL |
Local Loopback |
11 |
DM |
Data Mode |
12 |
TR |
Terminal Ready |
13 |
RR |
Receiver Ready |
14 |
RL |
Remote Loopback |
15 |
IC |
Incoming Call |
16 |
SF/SR |
Select Frequency/Select Rate |
17 |
TT |
Terminal Timing |
18 |
TM |
Test Mode |
19 |
GND |
Ground |
20 |
|
Receive Twisted-Pair Common |
21 |
|
Spare Twisted-Pair Return |
22 |
|
Transmit Data TPR |
23 |
|
Transmit Timing TPR |
24 |
|
Receive Data TPR |
25 |
|
Request To Send TPR |
26 |
|
Receive Timing TPR |
27 |
|
Clear To Send TPR |
28 |
IS |
Terminal In Service |
29 |
|
Data Mode TPR |
30 |
|
Terminal Ready TPR |
31 |
|
Receiver TPR |
32 |
SS |
Select Standby |
33 |
SQ |
Signal Quality |
34 |
NS |
New Signal |
35 |
|
Terminal Timing TPR |
36 |
SB |
Standby Indicator |
37 |
SC |
Send Twisted Pair Common |
See also the TIA,
standards