Parallel Port eprom programmers - suggestions

Roger Heflin rah at horizon.hit.net
Tue Feb 9 17:07:03 GMT 1999



On Tue, 9 Feb 1999, Andrew K. Mattei wrote:

> > Qbasic is nice for simple tasks.
> 
> Yeah, if it gets too messy, I'll go to C. Qbasic is quick and dirty,
> though. 
> 
> > The parallel port programmer I found claims to work on almost any
> > parallel port made.
> 
> I guess it depends on how it's designed...
> 
> The first one I built (off of a design on the 'net) used the
> bidirectional properties of the 8 data pins (at 0x378, pins 2-9 on the
> port). 3 out of the 4 computers I tried it on, it didn't work at all.
> The other one - I couldn't get two "reads" the same. Some computers
> don't take too well to this port being bidirectional. The way I designed
> this new one, I use the 5 bits on the standard LPT input port (at
> 0x379), and use the other 2 addresses (8 bits at 0x378 and 4 bits at
> 0x37A) as outputs. To me, nothing is really new here - I've done several
> control programs before using the LPT port. So it's really not that
> tough. :) If I get really industrious, I could do it in VB... But, I'm
> all for quick and dirty when doing things like this for myself... ;)
> Some places I won't skimp, but some, I will...
> 

I did some messing with parallel ports in the past.  I believe the
control pins can be used both ways (ymmv).  I had it setup so that the
8 control lines (5 on one control address, 3 on another) where all
used as input, and the 8 output lines were used as output, this seems
to work on a standard (386sx era) parallel port.  You need to switch
the setup bit to make the extra 3 work as inputs, but generally if the
designers of the port did not go to any extra trouble the bits will
work as inputs.  Then you need to use some mask instructions to make
it but the bits together.  I do remember that the 5+3 bits lined up in
such a way that not shifting was required, just mask and or.

			Roger




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