Real-Time Measurement and Control

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Check status of serial ports in cRIO-9068

Hello Everyone,


we are trying to control a ModBus slave via the serial port on a cRIO system. Normally this would be very simple (according to this guide) however it seems that we are not able to receive any signal from the slave device.

So, how can we check that the serial port is communicating with the slave modbus device? I can see in the VISA resources the ports being displayed correctly, therefore the cRIO identifies the port.

Should we pay attention to the cable used in connecting the RIO serial port to the slave device?




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Have you confirmed that the serial port(s) are working with a 'loopback test'? This will confirm if the serial port and cable are working. If you are using LabVIEW, there are VISA/Serial port examples that you can use for testing. As for cables, you should confirm if the Modbus devices' serial port is configured as a DTE, or DCE device, as that swaps the Tx and Rx lines. You may need a crossover cable. In other words, check you have the correct serial cable for the way the serial ports are wired on your devices.
David C
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