I have interfaced an AutomationDirect DL-06 PLC with our PC data collection application. The application on the PC uses InGear's Modbus TCP/IP driver.

I read and write to address areas in the PLC of V2000 - V4777. Everything seems to work fine but the application sends a zero to register V2446 to clear it and it will not write anything to it. The value stays the same unless I edit that value in the PLC program. Nothing is overwriting it.

I am using the new H0-ECOM100 with Modbus TCP/IP and have not put any special configuration in it other than the IP and Subnet Mask.

Works fine just won't write to some of the registers.

 

We are experiencing similiar problems with the ECOM module communicating with Modbus TCP/IP. Can you e-mail me the instructions you used to communicate. Was it the ECRX type instructions or ladder logic. [email protected]

 

You are contradicting yourself here. If the Modbus/TCP master were sending (writing) a 0 to V2446, then it *is* writing something: 0!

Then again, you would not be able to change V2446 with your programming software, and have the value persist, if the Modbus/TCP master were actually writing 0 to it.

My guess is that you have not correctly converted the octal DL06 addresses to decimal Modbus addresses.

If you're suspicious of the Modbus/TCP master you are using, I suggest you download one or more of the free (or shareware) Modbus/TCP masters available.