Assembler STRUCTURE FOR RESIDENT UNINSTALLABLE PROGRAMS
(use TASM).
This TSR source code can be easily modified to create many other resident
  programs (simply ignoring everything is not enclosed between bars).
Useful to write TSR's which intercept keystrokes, etc.
This particular program intercepts INT 15h (Sys Req function) to print the
  value of an electric resistance connected to Game port pins 1 and 3.
Use RESSHORT.ASM to avoid tons of comments.