Siemens S7-200 to SCADA cable pinout (Modbus)

[rtgibson]

Gents - hope somebody can help out, I've been tasked with fixing an OLD SCADA system. I've got an S7-226 PLC thats configured for Modbus comms via PORT 0 (on the PLC). I can see that in the PLC and the baud rate setup etc.

On the other end at the PC I have a USB to 422/485 converter - I can't for the life of me find a cable diagram on the internet, does anybody have a pinout diagram to connect from 422/485 to the 9 pin PLC connector ?

On the 422/485 converter there are 4 pins (well 5 - one for ground) TD-, TD+, RD-, RD+.

Thanks in advance.
Russ

 

[sigmadelta]

Here is an example:

Connect TD+ & RD+ to pin 3 on the S7-200 CPU port
Connect TD- & RD- to pin 8 on the S7-200 port
Connect SG (or GND) to pin 5 on the S7-200 port

 

[rtgibson]

Great

Brilliant - thanks for that.