Technical information

Newcom Parameters Serial Solutions
XON/XOFF Handshake.______________________
In the XON/XOFF handshake two characters are assigned
a special meaning by the serial port. One, called XON, is sent
by a device to signal that it is ready to receive data. The second,
called XOFF, is sent when the device can no longer receive
data. NewCOM therefore traps XON and XOFF characters as
they arrive and uses them to switch on and off the output of
characters. The user will not detect these characters. Interrupt
driven input sends an XOFF when the input buffer is nearly full,
and an XON when the buffer is emptied to restart the remote
device transmitting. Interrupt output is halted when an XOFF is
received, and restarted when an XON is received.
Beware!________
The driver does not check the data sent to it by the user
for XONs or XOFFs, which means that they are sent over the
serial line. The remote device will interpret these as XON and
XOFF, forcing it to stop and start transmissions. Likewise if the
user tries to send data which contains XONs and XOFFs to the
PC it will interpret them as such. This will not be a problem
with text data, which generally does not use the usual XON and
XOFF characters. Binary data could though be a problem, so
look out for the symptoms-data lost as buffers overflow, and odd
bytes lost because their values were the same as XON and
XOFF.
Chapter 2 Page 35