I have a compactRIO NI-9871 RS485 module that connects to a tested custom RS-485 DAQ device. I have done a loopback test on the 9871 using scan mode and it echos characters no problem. I have tested the custom RS-485 device using an RS-485 to USB with LabVIEW in Windows without problem. When I connect my custom RS-485 device (4 wire mode) to the 9871 in scan mode it echos garbage back. The device is only 2 metres away and not a noisy environment so I don't think I should need termination resistors. My question is, how do I know that the 9871 port is setup as RS-485 4 wire? In scan mode the tranceiver mode is not shown in properties, and it is also missing from the MAX COM port settings. I am thinking maybe the 9871 thinks it is in 2 wire or RS422 mode. Any ideas?
Thanks,
Rob Taylor