Thanks for reminding me about the F-Series PLCs, this may be the best solution.
I have been experimenting with the STX/ACK arbitration and clearly understand that it doesn't work reliably. This makes the use of the NS commands very difficult if the same COMM port is used for On-line monitoring.
I do have one question, "What is an XA command?"
In some cases where the STX/ACK arbitration appears to work, then I issue the NS command for Apending to a file, I sometimes find in the PLC Comm #1 input buffer the following string:
"@01XA58"
The next string in the the buffer is "<OK>", however the NS command did not complete correctly and the data appended to the file is corrupt.
I believe that this "XA" command was sent by the TLServer to the PLC after sucessfully arbitrating with the STX/ACK handshake. It seems as if the TLServer grants control of the COMM port (STX/ACK) but then forgets and resumes sending commands to the PLC without waiting for the "</>" terminator or a significant timeout.
I can't find any reference to the "XA" command.
Thanks for your advice.