CODESYS - the IEC 61131-3 automation software

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 Post subject: Modbus RTU Weirdness
PostPosted: Wed Dec 19, 2018 2:06 am 
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Joined: Fri Feb 16, 2018 5:39 pm
Posts: 18
Hi I was wondering if someone could shed some light on a bit of weirdness I'm seeing. I'll preface this by saying that I DO have experience with Modbus RTU. I use it to control Teco Westinghouse VFD's, Eaton VFD's, Davis Instrument weatherstations, and a few other odd bits here and there.

To start off with a new VFD brand I'm trying to just read from a single register. I'm trying to read from a Lenze brand AC Tech SMVector control VFD. According to the documentation drive register 19 should be the VFD Family which will return a value of 72. The drive register is offset by 1, so the modbus register I should be querying is register 20.

If I use my PC's Simply Modbus 8.1 modbus master software I can read register 20 and I get back a value of 72. If I use the PLC I get back a value of 0. Register 19 gives me 0, and register 18 gives me back a value of 150. Super confused because if I try to use register 18 on my PC I get back an error that it is an illegal data address, as it should be according to the documentation.

Wth is going on.


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 Post subject: Re: Modbus RTU Weirdness
PostPosted: Wed Dec 19, 2018 8:16 am 
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Joined: Fri Feb 23, 2018 3:41 pm
Posts: 141
read code 3/4 ?


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