Comm: a communication program for the IBM-PC

Comm is a minimal dumb terminal emulator for the IBM-PC under PC-DOS.  It  uses
BIOS  function calls for keyboard input,  allowing all control characters to be
sent with the conventional keyboard sequences. It uses an interrupt handler for
the communication port,  functional up to 9600 baud.  It is written in  C  with
assembler routines to handle I/O. It only supports the first asynchronous port,
COM1:.  It doesn't support setting the communication parameters.  This  can  be
done with the DOS "mode" command. The port IS NOT DISABLED (DTR is not dropped)
when the program is terminated; you must disconnect from the remote computer in
some other fashion.  As a result, however, you can exit to DOS, make use of any
DOS commands which don't tinker with the communication  port,  and  resume  the
terminal  session,  without any disruption visible at the other end (characters
sent to the PC will be lost in the interim).  Best of  all,  it  is  small.  It
supports very few commands, all of which are alt sequences:

alt-e is a toggle:  it turns echoing on and off (default off). This can be used
      for half-duplex systems.

alt-v is a toggle:  it turns verbose mode on and off (default off).  In verbose
      mode  characters  which  are  normally non-printable and aren't "carriage
      control" characters print as "^x",  where "x" is the character you  would
      hit to send the control character. Otherwise such chaff is ignored.

alt-b sends a break (approx. 300 ms. of line high)

alt-q quits the program, and returns to DOS