Redefine the parallel port? 
Author Message
 Redefine the parallel port?

I am using the parallel port for in/output to my own electronic
creations. It worked fine, but now I need more than the availiable
outputs. Usually I have 8 (single bit) outputs + 3 more that are used for
handshaking with the printer.
I need 15.
Then someone told me (and showed me) that is is possible to
"redefine" the parallel port, for up to 25 outputs! Is this true?
How do I do it? How do I address these outputs? Help?



Wed, 18 Jun 1902 08:00:00 GMT  
 Redefine the parallel port?


Quote:
>I am using the parallel port for in/output to my own electronic
>creations. It worked fine, but now I need more than the availiable
>outputs. Usually I have 8 (single bit) outputs + 3 more that are used for
>handshaking with the printer. I need 15.
>Then someone told me (and showed me) that is is possible to
>"redefine" the parallel port, for up to 25 outputs! Is this true?
>How do I do it? How do I address these outputs? Help?

There are two types of "parallel" ports: parallel port and printer port.
Parallel port was developed by Intel with the 8255 chip. In the PC family it's
used as simple printer interface (in a special mode). Some hardware developers
recognized, they need no "expensive" 8255, the interface can built from some
TTL chips. This is the printer port. The 8522 supports 24bit bi-directional
lines, the printer port dosn't. You need to build a multiplexer and control it
through the printer port. (Or get an old 8255 printer adapter!)

Regards
-BandiT-



Wed, 18 Jun 1902 08:00:00 GMT  
 Redefine the parallel port?


writes:

Quote:

>I am using the parallel port for in/output to my own electronic
>creations. It worked fine, but now I need more than the availiable
>outputs. Usually I have 8 (single bit) outputs + 3 more that are used for
>handshaking with the printer.
>I need 15.
>Then someone told me (and showed me) that is is possible to
>"redefine" the parallel port, for up to 25 outputs! Is this true?
>How do I do it? How do I address these outputs? Help?

How about adding a demultiplexer chip and output latches instead. This could be
done using simple TTL chips. Using a 3-to-8 demux chip and eight 4-bit latches,
you would get 8 banks of 4 outputs. This would require 3 "bank" output lines, 4
"data" lines and a strobe line. Using a 4 to 16 demux would allow up to 64
output lines.

This interface board would also put a hardware layer between your "creations"
and the parallel port, making it less likely that a mistake in one of your
boards will destroy the parallel port.

-- Jay

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| Jason Burgon - author of Graphic Vision, TV-Like GUI for 256 Colour SVGA |

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Wed, 18 Jun 1902 08:00:00 GMT  
 Redefine the parallel port?

OK, but my PC DOES have a 8255 port. Now how do I go about
using it for i/o? (remember, I need at least 15 output lines)
I'm NOT going to build a multiplexer. This is what I have done
in the past, and I want to avoid it, like my friend showed me on
the software he bought.



Quote:
> There are two types of "parallel" ports: parallel port and printer port.
> Parallel port was developed by Intel with the 8255 chip. In the PC family
it's
> used as simple printer interface (in a special mode). Some hardware
developers
> recognized, they need no "expensive" 8255, the interface can built from
some
> TTL chips. This is the printer port. The 8522 supports 24bit
bi-directional
> lines, the printer port dosn't. You need to build a multiplexer and
control it
> through the printer port. (Or get an old 8255 printer adapter!)

> Regards
> -BandiT-



Wed, 18 Jun 1902 08:00:00 GMT  
 
 [ 4 post ] 

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