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Hi there im trying to control a ABB ACS355 with Fena-01 adapter using modbus. i think i have a problem with the addressing. in the VFD i have all the parameters set and im abble to controll the vfd  with modbus poll. in register 1 i first send 1150 (also stop command) to set the vfd in ready mode after that im able to start the drive with 1151 (start command).  in the attachment ill uploaded my project. can someone help me out?

Thanks in advance




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Don't you need to CONNECT to the slave before you can exchange data?

Also, don't forget that Unitronics addressing starts at zero while MODBUS addressing starts at 1.  Be sure to account for the "off by one".

And you should change MB 1 & MB 2 in rungs 2 & 3 to positive transition contacts instead of direct contacts.

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There are example programs that came with your VisiLogic installation. I strongly recommend that you take a look at the one for MODBUS TCP Master. Look in Examples/Version 900/Project Examples/Communications/Ethernet/Ethernet MODBUS IP/V280_Ethernet_TCP_MODBUS_IP_Master.vlp

Your program still doesn't have a CONNECT function and you definitely do NOT want the SCAN EX FB. Also, what are you trying to do in Rung 6? You are attempting to communicate on every scan, and while that may be possible depending on the device you're trying to communicate with, your other communication functions will not work with that.

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I made some  changes to the programm but i'm stil not able to write to the vfd. also tried to set and reset request to send in rung 3, 4 and 5. I also tried to change the addresses  to 40000 and 40001 (according to the ABB manual and off by one) in rung 5 (previous rung 6) i try to write the speed for the VFD.

thanks for the tip according to the examples.


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  • 1 year later...

Gert, im doing a similar application with an ABB ACQ580 - Fena-21...


in your logic, you have vector length a 1. which makes sense in the logic that youve presented.


Did writing 1151 start the drive and 1150 stop the drive?


Did you read or write any more data to/ from the drive? 


in my application, im looking to also send a speed reference. Would i just increase my vector length to read  or write to another register in the drive?


Thanks in advance!

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The first thing to do is load the PLC, connect it to the drive, and determine if the logic works to start and stop the drive.  Have you had a chance to do this yet?  It's kind of the reverse of V'ger touching the Creator, if you're a Star Trek fan.  You can't beat actually putting the hardware together.  If it's a 480V drive you can wire a control power transformer backwards to light it up on your work table.  Just be careful that you don't electrocute yourself.

Once you've had a successful communication, you can move on to reading and writing other registers.  Usually you only write one and read many.  Modbus allows up to 125 contiguous registers in a Read operation.

As Flex pointed out, Official Modbus starts counting at 1 and Unitronics Modbus starts at 0.  4xxxx means it's a holding register, so ignore the 4 when determining the address.  In other words, Modbus 40001 equals Unitronics address 0 as Gert did in net 4.

Have a go at it and post your program with questions.

Joe T.


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Writing 1151 (start)  and 1150 (stop) does start and stop the drive, i also wrote the speed to the drive modbus adress 1.

In order to let the drive turn the other way you have to use negative numbers.

You can do this with writing multple vectors but i chose to create more nets and reading and writing  1 vector at a time.

I also made a net to read the actual speed at adress 4.

When you whant to read and write more data from and  to the ABB drive you can download the ABB documentation from their website with the modbus adressing table.

Gert P.

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