Now, Richard, before you refute all of this, I would never suggest such a setup had HW IIC not been standard in modern chips. SW IIC is a true 'performance killer'. Yes, I know that somewhere there is someone with a chip in his little hot sweatty hands that do not have HW IIC, but are we discussing "use a bent nail" or "a realistic way to do it"?

A commercial controller board, in this case, using an 805x MCU, might want the additional flexibility that a versatile I/O chip provides.
I see no such 'commercial application' beyond a 'devboard'. I can see amateur applications for such, however.

s possible, certainly, to create the facilities provided in the 8255 in a number of ways, they're definitely not simple and straightforward. There's room for debate about whether they're attainable at lower cost, though.
for "simple and straightforward" have a look at http://www.standardics.nxp.com/products/...ca9698.pdf 40 configurable pins for the price of two. or up to 8 '51 type ports for the same pins using http://www.standardics.nxp.com/products/...cf8574.pdf

aspect that hasn't been discussed much is the handshaking and interrupt generation capability of the 8255.
The 8574 has the same, OK, then it will cost you 3 pins.

use of discrete registers, latches, an/or buffers for these functions forces the designer to choose in advance of deployment,
If you design before you know what is needed, you are definitely not "industrial".

eldom have an uninterrupted hour in which to do this sort of thing, but I'll soon post an SCH3 and SCH4 jpeg file to represent a single I/O port, i.e. one with an 8-bit data channel, configurable as input, output, with handshaking and interrupt control as they'd be implemented in discrete HC-logic components, to do probably not all of what an 8255 or 6821 will do.
the datasheet for the 8574 show just that

ee problems of this sort quite often, as people come to me with devices that contain data that they want, but can't retrieve because their PC can't communicate with that kind of hardware. Perhaps that's why I'm so insistent on keeping the possibility of parallel interfacing by means such as the 8255 in mind, rather than discarding it out of hand. If you use a board with 8255's on it, you can do this stuff with a minimum of wiring and circuit design.
if you want a TRULY universal board stick a few of these http://www.standardics.nxp.com/products/i2c/ on it. should you need another, attach 2 wires and GO!

Erik