Hi,
i have just start to programming with opta plc by using ladder, i am tring to comunicate via modbus rtu by RS485 port. And i notice some problem thai i don't undestrand.
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when i use modbus function (like 02 or 03 etc) and i set the base adress (the first adress) the adress send by the opta on the bus is (my adress -1)
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I am tring to comunicate whit a relay modbus board. If i ceck the comunication on the bus (whit modbus pool) everything works fine but the plc does not read.
The plc show an error but in errorCode i have MbRqErr_Ok
Someone can help me ?
Best Regard
Stefano
It sounds like you're encountering a Modbus address offset issue with your PLC. Ensure that the base address in your PLC programming is correctly aligned with the Modbus relay board’s expected address. Modbus often uses 1-based addressing, while some PLCs might use 0-based, causing the address to be off by one.
For SIM Registration in the Philippines, make sure to double-check your information when entering addresses or IDs to avoid similar mismatches or errors.
Hi thank you for the answer!
How i can check this on the opta PLC programmed whit PLC ide ?
Best ragards
Stefano
I have also notice that:
If i write 0 on the base (first adress to be Red)
The PLC send on the bus FF FF in the start adress.
I have also try whit other modbus device the result Is the same
Unfortunately i am stuck whit this issue
Best regards
Stefano