4230-mmm & 4230-mmx.ib.rev4.doc
Page 12 of 17
17/10/2007
The RS-422 Standard
The RS-422 standard introduced in the early 1970s defines a balanced (or differential) data communications
interface using two separate wires for each signal. Due to the high noise immunity of the RS-422 standard, high
data speeds and long distances can be achieved.
The RS-422 specification allows reliable serial data communications for:
•
Distances up to 1200 metres
•
Data rates of up to 10 Mb/s
Only one line driver is allowed on a line, and up to ten line receivers can be driven by it. Figure 1.1 illustrates RS-
422.
(Ref: IDC Engineers Pocket Guide)
A(+)
B(-)
Com
Line Driver
Line Receiver
A(+)
B(-)
Com
10
1
2
9
RS-422
Transmitter
RS-422
Receiver
Balanced Line with
Differential Voltages
(-5V to +5V)
Up to 1200 metres
RS-422 Receivers (up to 10 devices)
Figure 1.1: RS-422 Connection
