From: utzoo!decvax!cca!chris.umcp-cs@Udel-Relay@sri-unix
Newsgroups: net.unix-wizards
Title: Re:  VT100/VT640 ^S/^Q and EMACS
Article-I.D.: sri-unix.3224
Posted: Sat Sep 11 00:14:56 1982
Received: Sun Sep 12 02:48:58 1982

From:     Chris Torek 
Date:     8 Sep 82 18:56:56-EDT (Wed)
VT100s and their look-alikes are all very slow terminals.  They
cannot even write text onto the screen at 19200 baud.  Therefore
they tend to send lots of ^S/^Qs.  However, they have a handy
"feature": nulls are not put into the FIFO; they are ignored as
soon as they come in through the serial line.  This means that
a carefully written driver for Emacs can prevent the terminal
from sending ^S/^Q by writing enough nulls after any operation
to let the operation finish.  The standard Gosling Emacs has a
driver for VT100s that works fine for up to 9600 baud, and uses
the special features of the terminal pretty well.  I modified ours
in an attempt to make it work with 19200 baud but as it turns out
this was pointless.  The Vax doesn't respond fast enough to the
^S from the terminal and the FIFO will overflow even if you're just
printing lots of text.  (Now we have an Emacs driver that works at
19200 baud on terminals that don't work at 19200 baud!)  Anyway,
the point of this whole letter is that you just have to write
lots of padding to VT100s at 9600 baud if you want to prevent
^S/^Qs.