Reception Overflow Flag
1: The specified number of bytes or higher has been received
at the Board/Unit (data continued to be received after the
Reception Completed Flag turned ON).
0: The number of bytes received at the Board/Unit has not
exceeded the specified number (data did reception did not
continue after the Reception Completed Flag turned ON).
This flag turns ON if the Board/Unit continues to receive data
after completing data reception.
The flag turns OFF immediately after the CPU Unit has completed
writing to I/O memory the data received using the
RXD(235), RXDU(255), or DRXDU(261) instruction.