From:	"Francisco Pastor" <etra-id AT etra DOT es>
Newsgroups:	comp.os.msdos.djgpp
Subject:	RE: I need to advice on timing...
Date:	Mon, 31 Jan 2000 09:41:16 +0100
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pwillard <pwillard AT mediaone DOT net> escribió en el mensaje de noticias
3T6l4.3418$i43 DOT 21114 AT typhoon DOT southeast DOT rr DOT com...
> I'm wondering if this is possible or not.
>
>     I need to touch external hardware through the parallel port and so
far,
> doing that hasn't been a problem.  Now, I need  to control the timing of
> signals sent to the external hardware.  I can sucessfully create a 50
> millisecond pulse using the 8259 clock stuff, but I have no clue how to
> generate a shorter than 1 millisecond signal.  I now need a 10, and a 50
> MICROSECOND signal and I'm not sure if I can.... IS it possible?
>

Yes, is posible to increase the timer speed 65535 times faster. You only
have to program the new timer divisor in the 8259 timer controler.
The MSDOS set the timer counter with the 0xffff value. With a inferior
varlue you get more ticks by second.
I use the 8259 to get a 10 mseg. and 1 mseg. wide pulse and work fine. To do
that you need:
- Calculate the appropiate timer division. The base frecuency is 1193180
counts by second. So, with a counter divisor of 65535, you get the 18.2
ticks / sec. The shorter pulse is inferior to100 nanoseconds.
- Know the register information for de 8259 chip
- Program a timer interrupt handler.
- Manage the interrupt controler to clear the timer interrupt.
- Bypass to MSDOS timer handler interrupt an interrupts each 55 msec. if you
are interested in use the MSDOS time services. If not, the time stop for the
MSDOS.
- When your program finish, restore all the changes.

Good luck.

Francisco Pastor

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