Westermo GDW-11 - Manual (Page 22)

22 6615-2203
=Termination
GDW-11 485
GDW-11 485 EX
Slave unit Slave unit Slave unit
GDW-11 485
GDW-11 485 EX
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
RS-422/485 general advice
Termination recommendations
The RS-422/485 line must be terminated. In the GDW-11 485 / GDW-11 485 EX, the
termination is combined with fail-safe functionality. The termination is used to prevent
undefined states when the bus is in tri-state condition.
… Using 2-wire RS-485 both ends should be terminated.
… Using 4-wire RS-485 both pairs shall be terminated at both ends.
… Using 4-wire RS-422 it’s only necessary to terminate the receivers.
RS-422/485 connection pins can be differently named. For some equipment 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.