Help Needed: Modbus Slave ID Conflict on WAGO 750-8208

CODESYS
1

Hello everyone,

I’m working on a project using a WAGO 750-8208 PLC and reading data from multiple Modbus slave energy meters over Modbus RTU (serial). I’m using the Modbus Configurator Tool to set up communication, and I’ve auto-generated the code for 5 Modbus slave devices.

Here’s the issue I’m facing:

  • I initially configured one energy meter with Slave ID 4, and it worked fine — communication and data reading were okay.
  • I then changed the Slave ID of the same meter to 5, updated the program, and downloaded it again.
  • Now, I’m unexpectedly seeing data appear under both slave ID 4 and slave ID 5, even though only one meter (with slave ID 5) is physically connected to the serial bus.
  • Strangely, in the slave ID 4 section, I see a timeout error, but the data values still change — and they match the values from slave ID 5, where there is no error and communication seems normal.
  • I’ve also tried changing the array ranges from the default 1..20 to 200..240 and 40..60, but the issue still persists.
  • I’ve verified that the Modbus Configurator tool is generating new code correctly after each change.

It seems like some ghost values or memory references might still be lingering for slave ID 4, even after changing the configuration.

I’ve attached an image showing the issue for better understanding.

Has anyone run into a similar problem before? Any ideas on how to properly clear or isolate the old configuration to avoid this?

Screenshot (5)
Screenshot (5)1366×768 73.7 KB

2

Hello Muhammad, have you tried to do a Clean All and then rebuilding your project?

image
image381×139 3.09 KB

Then do a fresh complete download, not an online change. Settings in the function block may have been initialized on your first download when you set slave ID 4. If you simply changed one value and did an online change instead of a full download, the settings for slave ID 4 might still be set in the function block.

1 Like