Question regarding the serial port on the CDP.

[JM K]

Hi,

I would like to know whether the serial port on the CDP emulates a serial port on a PC. With regard to emulation I mean does it provide power on the control pins of the 9 pin RS232 Port? I am facing a weird problem while trying to interface a PLC with the CDP.

I am able to interface with the same PLC over Modbus from an application on a Windows platform. The interfacing fails when I attempt it from the CDP. I have traced the signal and made sure that the relevant port is being opened by the application and signal is getting as far as the connector where the two cables (The DB9 Male end of the cable of the SCADA Master and the DB9 Female end of the PLC) are joined. I tested this by shorting the Tx and Rx pins of the connector (DB9 Male end of the SCADA Master) and have gotten an error as expected.

Any suggestions or advice would be very much appreciated. Thank you very much.

Best Regards,

JM

[Jesse Gilles]

The external RS232 port is setup to be a DCE port, so the RX and TX lines are swapped compared to your PC serial port (DTE). You’ll need to use a null modem adapter when you’re connecting the serial device to the CDP since the CDP is DCE and your external device is also DCE.

[JM K]

Dear Jesse,

Thanks a lot. Your advice/suggestion worked like a charm! Thanks again.

Best Regards,

JM

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