Issue
Serial communications are not functioning on a Modbus daisy chain.

Product Line
Serial Devices

Environment
Windows OS

Resolution
Portman is a free application that monitors and displays all serial and parallel port activity on either the local computer on which it is installed or on a remote computer. Portmon understands all serial and parallel port I/O control commands and will display them along with interesting information regarding their associated parameters.

A typical application where Portmon is useful: monitoring packets in a serial daisy chain. Simply connect a serial device to a computer running PortMon. The serial device will then act as a sniffer and Portmon can capture packet traffic in the loop.

How to Run PortMon

1. Run the PortMon executable (PORTMON.EXE)
2. Select Computer > Connect to connect to a network computer or Connect Local to connect to the local machine
3. Under the Capture menu, ensure that "Capture Events" is checked
4. Under Capture > Ports, select a port to monitor
5. Events at the selected port should appear in the PortMon window at this point
6. When you are satisfied with the captured events, you can Save the log file for future review

Where to Download:

Portmon can be found on the Windows website by searching Portmon or by following this link: https://learn.microsoft.com/en-us/sysinternals/downloads/portmon.