I have recently installed an instrument in my plant that, according to it's documentation; "uses the class 2 definition of Modbus/TCP and FC23." The DA servers I am currently using do not support FC23. I have already tried two vendors of OPC servers (Software Toolbox and Matrikon) and they have told me their servers do not support this function code. Is there anyone who knows of any software suppliers that write servers (preferably OPC) that support this function code? I have Omniserver in my plant and I can try to write my own code, but I've only done that with ASCII not Modbus and I would rather buy one that I know will work.

 

Just to be clear, do you mean the Read/Write Multiple Registers command? Plus by 'server' you mean OPC server, not end-device (server/slave).

This command merely allows one to do a 'read' (fnc 3) and 'write' (fnc 16) in the same packet. Why would any device require this? That is a bit hard to comprehend.

I agree that this function reduces packet count and/or increases update rate, but to require it either means the vendor is not very Modbus savvy or is trying to compel you to buy some software from them.

The good news is that I expect someone's Modbus OPC server probably supports this function because of either the increased performance or reduction in cellular data costs. I am not an OPC expert, but many of the OPC server companies watch this forum & like to offer their products

 

Hi Scott,

The MatrikonOPC Server for Modbus supports FC 23. Please get in touch with me so and i will get the support team to assist you in this matter.

Here is my email: [email protected]

Cheers,
Wassim