int.com  ---  written by John N. White for the Tandy 2000 with ms-dos 2.x
int.com allows a program to be interupted at any time (not just when a
function call is being processed).

To use, just run int.com (note: only run it one time after a bootup).
Then, to interupt a program, hold down both shift keys and the alt key all
at the same time untill the program terminates. The cs and ip registers
will be displayed.

This is a terminate and stay resident program. Every time an int 1C (hex)
occures, (from the timer, about 20 times a second) the location of the
routine that was being executed is examined. If the code follows the
end of the int.com code then a bios call (16h with ah=2) is done to check
the shift status of the keyboard. If the appropriate keys are being held
down, then the return address to the program is modified to point to
a program terminate function call in int.com .
If more than one terminate-and-stay-resident programs will be run, this
should be the last one because it may interupt any program that follows it.
int.com will not interupt code preceeding it so dos function calls and
system interupt handlers will not be interupted. This means that no interupt
will occur if a program is waiting for keyboard input as a bios call handles
that. Also, no interupt will occur if the keyboard hold is on.
Interupts must be enabled or the timer tick won't be seen. Normally programs
start with interupts enabled but in debug they start disabled. Interupts
can be enabled in debug by typeing rf followed by ei .