NI9871

[marcin3niu]

Hi. I am looking for an information about wiring 2-wire RS485 modbus device (Schneider Electric Altivar32 Drive Controller on RJ45) into 4-wire Rs485 NI9871 cRIO module (RJ50). Would somebody please correct me if I am wrong?  

TXD- should be connected with RXD- on DTE creating D0

TXD+ should be connected with RXD+ on DTE creating D1

D1 on DTE should be connected with D1 on DCE

D0 on DTE should be connected with D0 on DCE

Thanks, 

Martin

[PHarris · Accepted solution]

Hi Martin,

Thanks for using the forums.

Your wiring diagram is almost correct except for one connection. You have connected TXD+ with RTS+ (pin 😎 instead of RXD+ (pin 7) to make up the D1 transceiver line.

The following "Modbus over serial line" specification from Modbus themselves may come in useful for you if you refer to pages 24/25 and 29.

I hope that helps.

Kind Regards,

[marcin3niu]

Hi Paul,

Thank you for the reply.

Yes, you are right about the wiring diagram. It should be connected to RXD+ (pin 7) instead of RTS+ (pin 8).

 

Regards,

Martin Nowak

Process Systems Engineer

Metalysis Ltd