Westermo TD-23 - Manual (Page 20)

20 6600-2204
=Termination
TD-23
Slave unit Slave unit Slave unit
TD-23
Slave unit Slave unit Slave unit
Max 0.3 metre
=Termination
T+
T–
T+ T- T+ T- A B
R+
R–
T+
T–
R– R+ R+ T– T– B’ A’ B A T+ T+ R–
2-wire termination
4-wire termination
Termination recommendations
The RS-422/485 line must be terminated. In the TD-23 the termination is combined with
fail-safe functionality. For that reason it is important that the termination is used not to
get undefined states when the bus is in three state condition.
… At 2-wire RS-485 both ends shall be terminated at the other most units of the bus.
… At 4-wire RS-485 both pairs shall be terminated at both ends.
… At 4-wire RS-422 it is only necessary to terminate the receivers.
RS-422/485 connection pins can be differently named. For some brands the T+
corresponds to A, but other brands might use some other naming convention.
If a unit does not work it can help to swap A and B.
RS-422/485 general advice