AC500 Serial comms problem COM_REC

Hello

My sensor is connected to the AC500 Processors (PM591) serial port (RS232 with ACSII setup) and has carriage return(CR) to define the end of the string – I have sent this up and using the COM_REC I can read the sensors data. The data is being received ok but there is a problem.

I am using a terminal program on my laptop and connected to the processor via the serial lead (that is simulating my serial sensor).

If I enter 123456789 (carriage return) in my terminal , I get 123456789 in the PLC that is good and the COM_REC Done bit set.

But If I enter 666, for the next telegram, I do not get 666 I receive 666456789, therefore after the telegram termination (carriage return), the data is remaining from the previous telegram.

The problem is that when we get some comms error, the string gets bigger and bigger and eventually I get ‘*** string overflow***’ On Data_Com1 until the PLC power is cycled.

Please can you help and advice how why the data is not being cleared before the next string is read even though the function block is seeing the termination character (CR) and setting the done bit?

Thanks Matt