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These days I'm having a problem using modbus to reading pressure data from TROX terminal unit. It is kinda simple idea - 7 slaves (TROX units) and V700 is master and gets all the data. But as I'm conneting modbus though all of them I get error that there is no connection between TROX units. Slaves ID are set properly, cable polarity have been checked too. Maybe there are some other problems that I don't know? Thank you kindly for answers.

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  • MVP 2023

Thank you for posting.  We appreciate it!

The problem is you are calling the all the Modbus reads with the same trigger and you're not checking to see if the Modbus task is busy.  When you call a Modbus read block it actually spins off a separate process that takes a while to complete.  It also really helps to put a little breathing room via timer between reads.

I've modified your code to make a state machine cycle through the reads in order and slow it down to let the read function reset.  I know the examples show chaining read blocks one after another, but my experience has been this doesn't work.

You're probably going to have to update your version of Visilogic to open my file.

You can fiddle with the delay times to make it go faster.  You'll find that when you set them too low the blocks will hang up.

Let us know how it works.

Joe T.


Thermofisher JT.vlp

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