Hints - Westermo RS-232 Installationsanleitung

7.2 Line connection
4-wire
MD-45 Twisted pairs
1
Receiver A'
2
B'
3
Transmitter
A
4
B
Shield *)
5
*) If shielded cable is used, connect the shield only at one end to avoid ground currents.

7.3 Hints

RS-422/485 was designed for multidrop applications. When a system is installed it should
form a bus structure (see diagrams). Star shaped networks should never be created, there
are other Westermo products designed to work in star net applications. To get a correct
installation according to the RS-422/485 specification it´s very important that the line is
terminated at the correct points. The recommendation is to terminate the receiver on
the master unit and the final bus slave unit. See diagrams for details of how this is done
with RS-485 (2-wire) and RS-422 (4-wire).
The line transmitter used in the MD-45 is activated by data received on the RS-232
interface, unlike conventional converters that rely on a control signal (e.g. RTS).
If any problems do occur on set up of the MD-45, the LED's will be helpful.
• PWR: The unit has power.
• RD: Data received on the RS-422/485 interface.
• CTS: Follows RTS.
• RTS: Status of RTS from the RS-232 interface.
• TD: Data received on RS-232 interface.
A
B
=Termination
A'
B'
A
B
=Termination
N.B. R+/R–, T+/T– definitions are not standard, it can help to shift A and B
if the unit does not work.
28
RS-422/485
equipment
Transmitter
A
B
Receiver
A'
B'
Max 1 200 metres
B A B
B' A' B A B' A' B
2-wire
MD-45
3
Transmitter/
A/A'
4
Receiver
B/B'
Shield *)
5
Max 0.3 metre
A
Max 32 connections
A
Max 32 connections
RS-422/485
equipment
Twisted pairs
Transmitter/
A/A'
Receiver
B/B'
B' A' B A
B A
6157-2003