You need a device that makes DMA requests. A vanilla-type parallel port does
not do that.

For the fun of it I wrote a little assembly language program to directly
toggle the LPT port. When running under Win98se it was certainly very
glitchy as windows and interrupts took the processor away from it. Note that
even in Win9X access to the port is not direct. Rather, it is virtualized by
a VXD. Besides the glitchyness caused by windows there was quite a bit of
jitter that I attributed to the hardware.

I then ran it under MSDOS 6.22 and it was better, but still a little
glitchy, and no less jittery.

Finally, I added some code to disable all interrupts while it ran and that
cleaned up the glitchyness, but not the jitters.

Bob Ammerman
RAm Systems

----- Original Message -----
From: "Kyrre Aalerud" <kreature@C2I.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, January 22, 2003 6:17 PM
Subject: Re: [ot]: oscilloscope pulse display


> Can't you use DMA or similar to send a pulsetrain to a port at a specified
> speed?
> I recall something about this from my old soundblaster playback days using
> dual buffers etc...  That was dos, but I still wonder.
>
>     KreAture
>
> ----- Original Message -----
> From: "Herbert Graf" <mailinglist@FARCITE.NET>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Wednesday, January 22, 2003 11:53 PM
> Subject: Re: [ot]: oscilloscope pulse display
>
>
> > >>I have checked the pulse, on the parallel port of an older PC
> > running win98, using a CNC program,
> >
> > and the thing puts out a very nice 5volt square wave, it glitches once
> > in a while, I guess this is the noise spoken about, but it is doable to
> > do this in windows, or was....
> >
> > then checking my simple program again using a delay, it was no
> > better, it seems that if you remove everything except the statement
> > which turns on the pin, it will change it from 0 to 5vdc, but something
> > turns the pin off again automatically, some windows feature or function.
> >
> > So, like somebody said, it's back to the API or write another dll or
> > what ever,
> >
> > If any of you know the solution to controling pins on the parallel port,
> > your help is appreciated.... <<
> >
> >
> >
> > Which version of windows are you using? For any version of Win9x
> (including
> > Me) I haven't had any problems with manipulating the ports manually (I
use
> > inline assembler to do it). For WinNT (including XP and 2K) you need a
> > driver to allow direct access to the port. Harder, slower, but doable.
You
> > could always write your own driver if you really needed the speed, but
> > that's in the realm of "crazy talk" IMHO (writing drivers for windows is
> NOT
> > fun). TTYL
> >
> > --
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