When you use Moxa NPort to collect data from RS-485 two-wire serial port devices, you may encounter the problem that the Tx/Rx light of the serial port server is always orange during debugging, and data cannot be collected normally. This article takes Moxa NPort 5150 as an example to explain how to troubleshoot this problem.
I. Problem phenomenon
The software has connected to the Moxa NPort 5150, but cannot obtain data, and the serial port indicator is always orange.
II. How to troubleshoot
1. Check the wiring
Pay attention to the line sequence of the two RS-485 lines. Data+ connects to Data+, Data- connects to Data-. If the Tx/Rx light is always orange-yellow, first check whether the line sequence is correct. The following is the line sequence definition of the DB9 male connector of the Moxa NPort 5100 series serial port server.
Note: The Data+ of Moxa devices is the B line, and the Data- is the A line. This may be inconsistent with the definition of the AB lines of other manufacturers' devices. When troubleshooting the line sequence, you can try the reverse connection.
2. Adjust the pull-up and pull-down resistors
If you confirm that there is no problem with the line sequence, you can try to adjust the pull-up and pull-down resistors of the device.
Remove the device casing, find the JP3 and JP4 jumpers, and use the jumper cap to short-circuit the two jumpers, as shown in the following figure:
Note: The pull-up and pull-down resistor jumper positions in the above figure are only applicable to Moxa NPort 5100 series products. For the pull-up and pull-down resistor positions of other models of devices, please refer to the manual of the model device.
The above method is applicable to serial devices that use 485 communication, such as the NPort series of serial device servers and the MGate series of protocol gateways. If the problem is not solved after following the above steps, please contact Moxa technical support .