Hardware Manual for the PCD2.M5 Series│Document 26/856; Version EN 12│2014-07-24
Saia-Burgess Controls AG
Definitions of serial interfaces
Annex
A-3
A
A.2.2 RS-485/422
Signals to RS-485 (RS-422)
5V
2.5V
0V
4V
3V
2V
1V
VOH
VOL
VOZ
nicht aktiv
z.B. Startbit
/TX
TX
mark
space
= mark
VOZ =
0.9 V min ... 1.7 V
VOH =
2 V min (with load) ... 5 V max (without load)
VOL =
-2 V ... -5 V
In the idle state, RS-
422 is in the “mark” position
RS-422:
Signal type
Logical state
Polarity
Data signal
0 (space)
1(mark)
TX positive to /TX
/TX positive to TX
Control/message
signal
0 (off)
1 (on)
/RTS positive to RTS
RTS positive to /RTS
RS-485:
Signal type
Logical state
Polarity
Data signal
0 (space)
1(mark)
RX-TX positive to /RX-/TX
/RX-/TX positive to RX-TX
Not all manufacturers use the same connection configuration, so the data lines may
need to be crossed
To guarantee error-free operation of an RS-485 network, the network should be
terminated at both ends. Cable and line termination resistors should be selected in
accordance with manual 26/740 "Installation components for RS-485 networks".