RE: [CAD_CAM_EDM_DRO] p-port alternative 8255PPI was Re: troubleshooting help

|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.

Ok, that says a lot about what we can expect to see with today's PC's -
nothing programmable and no extra pins.

|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.

Ah, yes - good old "value engineering" at its finest! :)

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

Something that I didn't realize.

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

This is true, and it offers a carload of operating modes from simple I/O
that we'd use to a complex bidirectional handshaking mode that uses several
of the lines.

|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.

Now, are there any PCMCIA cards that use this port? I know that Dave
Goodfellow mentioned a source for a parallel PC-Card, but I'm guessing that
this is a printer card rather than a "true" parallel port card.

|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)