BECKHOFF KL6001 - Manual (Page 16)

Data transfer, function
16 KL6001
BUF_F:
BUFFER-FULL_Flag The receive FIFO is full. Data that is now received is lost.
Error handling If a parity, framing or overrun error occurs, the data item concerned is lost,
and it is not loaded into the terminal’s receive FIFO.
Incoming data is ignored if the buffer is full.
The corresponding diagnostic bits are set in R6 if an error occurs.