The use of XON/XOFF ususally assumes a data exchange that relegates "control characters" (0-1FH)for protocol or formatting. Also there is no convention for "stopping distance" when you receive XOFF whether there be a few more bytes has in the past been manufacturer specific.

If you intend to send binary data. A protocol wrapper is usually required. This protocol wrapper would typically "packetize" the data.

Each packet most often indicates Start Of Packet (for synchronization) Message Type (data format or Type), Length of Record (byte count), Payload (data), and Error Control (LRC/CRC/FEC).

An ACK/NAK exchange with or without message numbering typeically ensues. If you buffer is sized to the packet length you can delay the ACK until you have "unloaded the buffer" as long as this time does not exceed the "Waiting for ACK Timeout".

If you overflow your buffer your data type will determine what ammount of trouble you are in. If it is audio you have lost a fram e and "clicks", "pops" or silence can result. If you are controlling a CNC machine you may have just "destroyed" the work or the operator.

regards,
p