Modbus Communication using Special Message Framing AC500 via Emerson Floboss
Hello,
I am using Modbus RTU communication at AC500 PLC via Emerson Floboss 107 flowcomputer.
There are some special historical data registers that I need to read. It doesn't work like standart communication protocol.
Instead of "Number of data", "Number of index should" be send to device. ( Number of data is already defined at the device).
Message framing is like;
01 03 00 B6 00 0C XX XX (01 as adress, 03 function code, 00 B6 as hex of register 182, polling for index 12)
With this way, I can use NB ( Number of data ) input of COM_MOD_MAST block. But I get error of "8215" Invalid length.
I can see reply of slave using Modbus test software, and this's how it works at slave side.
Slave actually sends data that I need, but COM_MOD_MAST block does not write data to my variables because of this error.
How can I overcome this error? Is there a way to make COM_MOD_MAST block to ignore this error and write received data to my variables?
Answers
Hello!
Are you using the exact number at NB as the it send back from the slave?
Maybe you have to use ASCII and COM_REC/COM_SEND and define this telegram as it is asked for by this Emerson component...
I know it is not an answer but a suggestion.
br
Gustav
If I use exact number, I can see data. But that exact number is an index. I can't get another indexes, because data number at NB and index does not match.
I tried to generate Modbus telegrams using Syscomlib, but couldn't manage to do it. ASCII and COM_REC/COM_SEND sounds better. Will try
May be attached datasheet will help you.
You have to configure com port as ascii in control builder.
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