Connecting to a DESPATCH protocol 3 using Modbus

Hi Guys,

I’m not sure if anyone has used a Despatch protocol 3, it connects using MODBUS TCP protocol, i have the OPC-UA connection with Ignition but i am having issues trying to read the registers.

I’m new at this and was hoping someone would have some pointers on how to setup a tag to talk with a register. I tried browsing but nothing shows up so im guessing that they do not use the standard protocol from what i have read. Thanks

The Modbus protocol doesn’t support browsing - you need to know what data you’re after and where it is.

So, once you have your device connection set up, the next step would be to create a SQLTag in the designer with an OPC Item Path that looks something like this:


Which would address Holding Register 1 on the device… see … essing.htm for more on Modbus addressing syntax.

Thanks for your reply, if I figure out what the addresses are can I use address mapping to get OPC-UA to browse?

Sure, but the mapping is generally only useful when the data you need lies in contiguous registers and is of a homogeneous data type.

Thanks, for instance if the registers are Holding registers and go from 8243 to 8253 than I could setup mapping but since my registers go: 8243,8244,8249, 8250, 8251, 8256,8258

I cannot setup mapping? Thanks again

Assuming all the data you need is a 16-bit datatype you could still map it… you would be mapping some unused registers as well. Which if you dragged the whole folder in from the browse would be read as well, potentially causing problems (depends on if the device has data there or not and decides to return an error).