p-port alternative 8255PPI was Re: troubleshooting help

Jerry,

Last question first: No, we only get 17 useful pins from an IBM p-
port. IBM did not use the "then standard in Z80 computers" 8255PPI
(Programmable Peripheral Interface) chip in the design of the PC.

We tend nowadays to forget the cost issues that faced them, as they
attempted to enter the "consumer" market. The 8255 WAS an expensive
chip, compared to the '244 and '245 they DID use for the p-port.

Also we forget that the PC originally supported 4 p-ports(of 3 bytes
each), but DOS only supported/supports three.

However, the good news is that the 8255 is no longer anywhere near
expensive! And there are MANY designs for boards using it which fit
in a pc slot. One is at:
http://www.boondog.com/%5Ctutorials%5C8255%5C8255.htm

There was also an article several years back in one of the pop-
tronics type magazines, using the 8255 for a plotter, with board
layout and programming notes.

It is a very easy chip to use. A yahoo search on "ibm 8255 ppi" will
give many useful hits...

There are also SCADS of 8255 based I/O cards available ready made.
Many support more than 24 pins of I/O by using multiple 8255's.

I often wonder why more pc based CNC controllers don't support other
than "standard" p-port addresses so cards like these could be used
for I/O. (ah-ha! is one which does support non-standard addresses)

Hope this helps.

Ballendo


--- In CAD_CAM_EDM_DRO@y..., "Carol & Jerry Jankura"
<jerry.jankura@s...> wrote:

> Alan:
>
> I don't know how this fits into the equation, but you'll remember

that the first printer ports used an 8255 parallel port interface
chip. In addition<snip>
Does it still mimic a complete 8255? If so, does it make any sense to
program the chip? Is it possible to get at all twenty-four pins that
the 8255 originally supported?

>
> -- Jerry
>
>