Hi Folks,

I'm setting up a Alicat Mass flow controller with the Modbus TCP client.  I've configured the IP address of the device and can read it via its on-board webserver from my browser.

But no matter what I've tried I cannot get the device to return data to my data block.  I keep getting Error 818D.  I've tried every form of data that is 32 bits in the data block.  I've tried adding 1, 10001, 30001, 40001, 400001, and nothing to the register.  But still 818D keeps getting read.

Here is 2 minute Loom showing my problem:

Troubleshooting Communication with Alicat Mass Flow Controller 🛠️ (loom.com)

What do you think experts?

Update: I've deselected optimized block access and since the data length is 32 bits I've set the data length to be 2 each register to scan.

After doing this I now get no errors but instead a busy signal.  There is nothing else using the Modbus TCP device at any point during the scan.

Any ideas?

SOLVED!!!!!

In the MB Client instance data block the MB_Unit_ID has to be set to match the device.

This was incredibly odd since Modbus TCP/IP doesn't really use a slave address.

The Default value was set to 16#FF AKA 255.  When I set the value to 1 the server started reading.

https://www.loom.com/share/7482425486ec447eb1c289dc3e1299dd?sid=fe48f420-e771-4176-bc5d-3139764efb5b