UCCXMGM@OSUCC.BITNET (10/09/90)
Index Number: 10944
[This is from the BLIND-L mailing list]
A couple of weeks ago, I posted a request for
information regarding which interrupt would be best to use
for driving the output of a screen reader program on which I
am working. I would like to thank those who responded and,as
I said, I will share what I have found out so far.
The real-time clock-tick interrupt, both int 8 and 1C
hex play an important part in many TSR background processes.
Int 8 occurs when the timer ticks and thus none of the things
which were supposed to happen on this interrupt have happened
yet unless something rerouted the interrupt after the TSR was
installed. Int 1C hex is the last interrupt to be called so
it is a good one to use if you want your TSR routines to
execute after all other timer-dependant routines have
executed.
I ran "PRINT.COM" and looked at the interrupt table in
segment 0 and noticed that several interrupts were rerouted.
The only two periodically activated ones were 1C and 28.
The others were for such things as the serial I/O routines in
the ROM BIOS, the disk controller, and the multiplex
interrupt. If anybody is not familiar with that one, it is
interrupt 2FH and is used by well-written resident programs
to keep someone from reinstalling them. Int 28H is the busy
loop for the keyboard interrupt. loop for the keyboard interrupt.