General Category > Support Questions

'Illegal Function' and 'Illegal Data Address' messages

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Aviraj:
Hi

So I have an HMI with a bunch of Pilot Lights connect to check the status of some inputs and outputs on the PLC. I am pretty sure that the PLC addresses are correct because I initially tested them on a similar PLC. So now when I run the HMI, I see a message saying 'Illegal Function' on the pilot lights connected to the outputs and 'Illegal Data Address' on the pilot lights connected to the inputs.

The input addresses are like 12051, 12054, 12055 ... and the output addresses are 02053, 02054, 02055 ...., and these were tested to work on another similar PLC (DirectLogic 06 DO-06DD1)

I haven't really come across these message ever before !

Thanks in advance for the help

Aviraj

Archie:
An address that starts with a 0 will use function code 1 for reading and function code 5 for writing.

An address that starts with a 1 uses function code 2 for reading. There is no valid function code for writing.

Make sure you are not using 1xxxx address in PLCAddressClick. Make sure your PLC supports function codes 1,2, and 5

Aviraj:
So where am I suppose to list the function code ? In front of the PLC Address ? Like 212021 ? That gives me an illegal address message because the addresses are supposed to start with a 0 and a 1

Thanks
Aviraj

Archie:
The first digit of the addresses tells the driver which function code to use. If your address srarts with a 0, the driver will use function codes 1 and 5.

Under the Tips and Tricks section of this forum there is a topic on Modbus addressing that is very helpful in understanding it.

Aviraj:
Ok, I will have a look at the forum and I just confirmed that the PLC actually does support those function codes.

http://www.automationdirect.com/static/manuals/d006userm/d06uservol1.pdf

Page 142, it states it as 01, 02, 05 etc.

So when I explicitly add a 01 in front of the output address, e.g. 0102053 to read the state of the output, that 'Illegal Function' message does not show! However, I still cannot see the correct state though.

Thanks a lot

Aviraj

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