CODESYS - the IEC 61131-3 automation software

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PostPosted: Tue Aug 21, 2018 8:15 am 
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Joined: Mon Jul 09, 2018 8:23 am
Posts: 5
Hi,
I'm using Eaton PLC XC303 and I'm trying to make PLC as a Modbus slave.
And there is a problem, I can't use holding registers to read and write them.
I can't write values to the registers from PLC side. Why?


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PostPosted: Tue Aug 21, 2018 8:33 am 
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Joined: Fri Dec 26, 2014 3:10 am
Posts: 45
Hi marcin.w,

if the PLC are using codesys V3, just make sure you have configure the device properly and make sure you have add the IO channel correctly.

if you use holding register just make sure you have add the IO channel for FC 03(reading) FC06 or FC16(for write)

Thank you
John Lee


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PostPosted: Tue Aug 21, 2018 8:57 am 
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Joined: Mon Jul 09, 2018 8:23 am
Posts: 5
You don't understand me. PLC is a slave, not master, so there is no any channel settings.
And yes, PLC is on Codesys v3.


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PostPosted: Tue Aug 21, 2018 7:19 pm 
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Joined: Sun Jun 28, 2015 12:23 pm
Posts: 64
Does your device have the Modbus slave licence? My preferred Codesys plc has a Modbus master, but will not act as a slave due to not having the licence.
Some genius has probably written a Modbus slave library :)


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PostPosted: Wed Aug 22, 2018 3:52 am 
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Joined: Fri Dec 26, 2014 3:10 am
Posts: 45
Hi marcin.w,

As normal standard Codesys V3 soft PLC, regardless your modbus master or slave, you have to do the configuration.

The step for configure as slave is adding the device->add modbus slave->add modbus serial device.

Then inside the modbus serial device have the memory where is for outside using reading holding register to read or write.

as for some other brand PLC like ABB, Wago , where default have open up the modbus slave function where will automatically to map all the PLC internal memory for all the modbus function.

this is example for standard codesys V3 softPLC modbus setup

Thank you
Lee Junn Hei


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PostPosted: Thu Aug 23, 2018 10:21 am 
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Joined: Mon Jul 09, 2018 8:23 am
Posts: 5
ph0010421 wrote:
Does your device have the Modbus slave licence? My preferred Codesys plc has a Modbus master, but will not act as a slave due to not having the licence.
Some genius has probably written a Modbus slave library :)

Eaton Codesys doesn't need another license for Modbus slave ;)

johnlee wrote:
Hi marcin.w,

As normal standard Codesys V3 soft PLC, regardless your modbus master or slave, you have to do the configuration.

The step for configure as slave is adding the device->add modbus slave->add modbus serial device.

Then inside the modbus serial device have the memory where is for outside using reading holding register to read or write.

as for some other brand PLC like ABB, Wago , where default have open up the modbus slave function where will automatically to map all the PLC internal memory for all the modbus function.

this is example for standard codesys V3 softPLC modbus setup

Thank you
Lee Junn Hei

Yes, I know these all things.
P.S.
I've got answer from Eaton support, that the problem is with the Eaton Codesys.
So probably they will fix it in the next version.

Thank you guys for help. For now that's all. Bye ;)


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