Modbus TCP slave for Epic

Hi, I am using the modbus integration tool for modbus slave, when I try to connect with modscan, exception response was shown, the subroutine status show -441 which not identify under the possible status code from the integration tool. May I know what problem with this or do I missed any configuration?

Since this is an EPIC, I don’t think you can use port 502. Select a port above 1024.

Also you can get most of the error messages from the error codes by going to Help, Error Lookup in PAC Control. The -441 is “Not listening on socket.” which is likely because of trying to use port 502.

Do you mean I should make it SetCommunicationHandleValue(“tcp:1025”, chModbusSlave); by changing port 502 to port higher than 1024? However, the firewall modbus TCP was set as port 8502 and my modscan is connecting with the device IP with port 502.

Yes, the 8502 one is used by the MMP Server to access the memory map using modbus, so you can’t use that one. I like to use port 10502. You will also need to enter a firewall rule for the port you pick.

Okay. Understand with it. Thank you for the explanation.