I have multiple PLCs I need to communicate with and in the interest of reducing the number of read requests was thinking I should bring all the information I wanted to read into one PLC and read everything from there, then write to the individual PLCs when writing out a value. This is what I used to do when using Visual Studio as an HMI. I am not sure how to set this up in Ignition, to read over 1 device , but write to the others.
However, if I read from 1 device I have more than 125 tags. Will it make multiple requests for the rest of the tags?
What is the best way to approach this so I can avoid slowing anything down.
Don't consolidate into one PLC. Instead, ensure that in each PLC, the various bits and words are allocated consecutively (no gaps), so that Ignition can read the largest possible amount of useful information per request. (The span gaps setting lets Ignition read across unused addresses, but that data is still passed on the wire. And you need more requests.)
Also, make sure that you use a single poll rate per consecutive block. Requests at different rates cannot be optimized together.
(That 250 bytes in a 125-register read really is the largest request the Modbus protocol can make. It's just not a very fast protocol.)
Thank you, as I started to look at it more that seemed like it might be the way Ignition handled it. This is my first time using modbus in Ignition and I was structuring my communication for what I used in the past. In a way Ignition makes the handling of communication easier for modbus than my past programs.