They don't provide enough output current to do useful work. Of course, neither do most 805x's, so it's no loss when comparing the ports. Likewise, the CMOS versions are, again, similar in their capabilities.

I don't like 'em, though. That doesn't mean I won't or can't use 'em if it looks practical. If I just need 4 mA to drive a LED, scan a keypad, or only have to drive a CMOS-input device, it's adequate if the cable is short. I've NEVER designed one into a board. I've put them on existing boards that I've use to adapt to other existing hardware. I've programmed for them on commercially acquired boards from, say, Intel. That hasn't made me like 'em though. Even when my task requires a large RAM buffer, which demands an external memory bus, the various LSI's for I/O aren't the first things that come to mind if I have a requirement for more I/O.

I haven't bought 8255's since back in the '80's, just for the record. Once AMD's MACH-2 series of CPLD's became available, I built my I/O expanders with them unless I needed even more current.

Unless the output current requirement is really small and space is very limited, I prefer bipolar parts, or, if available, their CMOS equivalents, provided their output is sufficient to do the job. Back when they were available, I used the 74BCT2424, which had a 64mA output per pin to expand output.

Now THAT would drive a relay or light up a LED! It didn't readily interface to an 8-bit device, as it had a 16-bit bus, but it could be done and certainly was worth the trouble when it was needed.

RE