Manual

Escape Sequences 6-9
Xon/Xoff Handshake:
The DEC <Xoff Threshold> parameter specifies the number of empty bytes remaining in
the buffer when the <Xoff String> is to be transmitted. The default is 80. The number
should be large enough to allow for any latency within the host, during which the host
continues to send characters before recognizing that the Xoff String has been transmitted. If
the Xoff Threshold is set greater than or equal to 128, the Xon Threshold is automatically
decreased so that the sum of the two is equal to the buffer size minus one.
If the second parameter is not defaulted or zero, the Xon/Xoff handshake is not enabled.
(Xon/Xoff is also disabled if the <Xon Trigger String> parameter is null, or if no Xoff
Trigger String has been established via an
ESC.N command.)
The STR <Xon Trigger String> parameter sets up the string which is to be transmitted
when the number of characters in the buffer falls to the Xon Threshold. Default is the null
string. If this parameter is the null string, the Xon/Xoff handshake is disabled.
Example: the string
ESC.I100;;17: establishes an Xoff Threshold of 100 characters, such
that the ASCII DC1 character (character code 17, also known as XON) is sent when 100
empty bytes remain in the buffer. The Xoff Trigger String must be established via an
ESC.N
command.
Example: the sequence
ESC.I;;17:ESC.N;19:ESC.M10: establishes a "normal"
XON/XOFF handshake (using the ASCII DC1 and DC3 characters) with a 10 millisecond
turnaround delay.