JiM_cz

Modbus RTU communication with Altivar VFD

7 posts in this topic

First of all, I'm very new with Modbus so please bear with me. I have a PLC program where you can set a VFD speed on HMI. Please see the attached pic. I understand that the values I'm moving into the registers mean:

#1 slave no

#6 I want to write

#4 ??? (not sure what it is for)

#2136 Where into the VFD I want to write (frequency)

D6200 The set speed from the HMI

But what I don't understand is where the addresses D32300 - D32304 come from? Where is it defined that the modbus will be using these particular ones? I went through both the Omron card (CP1W-C1F11) and the VFD documentation but I can't find anything about it.

PLC prog.png

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1. What PLC?

2. Where did the code come from?

3.  Are you using Modbus function block?

4. Please post more code.

 

 

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Posted (edited)

It's CP1H PLC and it's a program in an existing machinery  that I'm trying to understand and modified. There is actually a small portion of FB but I'm not sure what it's doing and if it's related to the modbus frequency command but I don't think so. The code I posted is almost all that is there as far as the VFD communication is concerned. Then there are just zeros moved to 32305 and 32306. See the attached FB please.

aUntitled.jpg

Edited by JiM_cz

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Good call Wasan! :dance:

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Thanks a lot for yr help guys. It's a bit clearer now. Btw, would Modbus with a CP1L processor look different? The provided material says the  Easy Modbus Master is only for CP1H...

Can you also tell me what the Function Block might be used for?

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