One normally uses an encoding scheme that does not involve raw binary
data over the serial connection -- Postscript can display bitmaps, etc.
When raw binary data is used on a port, one must disable all in-band
flow control, and this can lead to problems with the communications
link. When in-band flow control is disabled, the XON and XOFF flow
control characters are treated as data.
One uses SET TERM/pasthru (one `s') or (obsolete) /passall. With the
former, specifying /nottsync and /nohostsynch disables the flow control.