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).

What did you use to physically connect a despatch protocol 3 controller to the pc to send modbus with? I am trying to get one of these to work right now too

We used Kepware UCON to Modbus TCP to connect it to the ignition gateway.

Why did you need Kepware in the middle? Does the Despatch not use Modbus itself?

Phil - you unknowingly replied to a topic about a Despatch oven about a year ago: Automation Professionals' Advanced Modbus Driver - #22 by pturmel

The issue we found with the Protocol 3 is that it uses Function code 23 to edit profiles - I believe you added functionality in your Modbus module.

We ended up specifying Watlow F4T controllers on new Despatch ovens. The costs are a bit more than the Protocol 3 but the engineering hours saved in working with the Modbus protocol is definitely worth it.


Ok, I didn't make the link with Despatch.

the despatch I am trying to connect uses modbus out of 2 DB-9 cables (one for input, one for output), which is why I am trying to see how one gets a DB-9 to send modbus to ignition when it is on an ethernet network

I guess what i am trying to find out is

would a DB-9 to RJ45 adapter work to send modbus to ignition over a network and not having to directly have the machine plugged into my pc?

or would I need something more along the lines of a MOXA gateway 3180? because its not as simple as the first option.

is a moxa basically the same idea as using a kepware UCON? just with a moxa instead?

I have heard great things about these Moxa's , and I am pretty sure it was from you

Hmm. Not sure why you would need two cables. I would expect a single cable to handle both directions.

But yes, you will need something to make the serial interface available over ethernet.

I don't know if the Moxa gateway will pass function code 23, if you need that. If you do need it, you will need to use my Modbus module instead of IA's native driver.

If you use a raw serial to TCP Moxa device, be sure to read the usage notes in my driver's manual--applicable even to IA's native driver.

( I know essentially zero about Kepware UCON. )

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