Modbus Functions


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Hi, Simple question this time.... where can I find documentation on the modbus functions - I'm sure I've seen it in the past somewhere but when I need it at 12:05am I'll be blowed if I can find it anywhere - I've searched the online documentation and can only draw a blank - I can see the functions listed in the modbus functions section but no details of the parameters for each.

By the way, I've given up trying to use channels to set outputs in my OptiLogic RTU - no matter what I try I cannot stop the timeouts even though I can see that the i/o takes less than a few 10's of milliseconds and I set the time out to anything between 10ms and 10s. :-(. Mainproblem is that once I get a timeout the output is not set as required.

so for now I just want to get outputs set reliably when I set them - +or- a second or two time wise I don't mind, and I've only got two digital outputs I'm really interested in. I'm reading 4 digintal inputs 3 analogue inputs and 2 counters - not really ground braking stuff but I can't make it work reliably. So its back to function calls so I can at least catch the errors and retry (if I can find the documentation that is!!)

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The protocol docs are in the user's guide under serial / ethernet communications. There is a sub-chapter called predefined protocols and a section on modbus. Really there are only 4 modbus functions (ok, 5), the difference in all the I/O types refers to how the data is interpretted.

Are you connecting to more than one device on a 485 chain?

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