Link Layer Error code-4 for ML-1400 SERIES A

hello ALL

as per my previous post i am trying to communicate ML-1400 SERIES-A arduino(ATMEGA328) serially

so i have made arduino as a modbus master and PLC as a modbus rtu slave
i have downloaded the MODBUS MASTER library for arduino
so now i have following hardware

ml-1400 series a
arduino freeduino(ATMEGA328)
RS232-TTL CONVERTER

i have set channel-2 as a modbus rtu slave

but when i connect both device serially
on the PLC channel NO-2 status it is showing
LINK LAYER ERROR COUNT-1
LINK LAYER ERROR CODE-4

please tell me why this error is coming
and i think because of that on the com port of ARDUINO it is showing some unexpected characters



please tell me how to fix this

thanks in advance

Did you ever get a solution for this?

I have a customer in France with the same issue. Different PLC but same link layer error. I suspect their RS485 config is in error but I am not sure.
Mike

Mike,

What is similar about your application; the PLC brand, PLC model, protocol, or the Arduino library ?

The OP didn't give us nearly enough information to work with; a screenshot of unprintable characters isn't as useful as a hex dump.

Usually link layer errors are due to noise on the line or to a configuration problem like the wrong parity or stop bit settings.

The similarity is strictly in the link layer error. I am working blind with a customer overseas. I have not yet gotten them to divulge their modbus master equipment.

I suspected a very basic communications issue but I have to send requests one at a time.

I have an ML1400, they have (I think) some kind of Siemens equipment.

Baud, parity, etc have all been verified. Trying to get them to terminate at each end.
Mike