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Vision and Modbus cable pinout

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Am trying to connect a Vision 120 to a Trihedral VTS Scada usng Modbus RTU serial but am having difficulties with the DB9-RJ11 pin out.

I understand it should be

RX 2 -> 3 TX

TX 3 -> 2 RX

DTR 4 -> 6 DSR

GND 5 -> 5 GND

GND 5 -> 1 shield

DSR 6 -> 4 DTR


PC side: RTS 7 -> 8 CTS

PLC side: RTS 7 -> 8 CTS

PLC side: cable shield to 1 Shield

If this is right, what do I do with 7 and 8 PLC side if the RJ11 only has 6 pins??

Don't suppose Unitronics would have a Modbus DB9-RJ11 cable, would it??

Any help would be greatly appreciated.


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I'm assuming that the scada is running on a PC with a real serial port.

The PLC doesn't use the handshake lines. Have you tried using your programming cable as the interface cable? It should work fine.

Joe T.

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