Well, the saying is "let sleeping dogs lie."

I don't know how you're bit-banging 10000 bits per second, but unless you're doing 20-30 channels at once, each at a different baud rate, it's not taxing your 100 MIPS MCU, and, even then, you could easily do it with an 8255 from a slow-cycle bus, yet still maintain your 100 MIPs rate, as the slow-down would be impreceptible. After all, just the external bus accesses would be slowed down. All the timing would still proceed at full speed. You keep ignoring that. I don't mind, though, as it gives me an opportunity to point it out.

I don't care what YOU use, Erik. I just object to your blanket statement that anyone who'd even consider an 8255 for his parallel I/O is making a mistake.

The application requirements may not demand a high-speed MCU. Old and slow might fit just fine, but even if the application require a faster MCU, with a slow external bus cycle they'd work in many applications. After all, you get 24 bits of I/O for about $4 in unit quantity, and about half that in hundreds. The I/O is as hefty as any of the MCU's one might be tempted to use.

If I were to encounter an application, I'd not hesitate to use 'em, though I'm not looking for such an oportunity. Economics should, of course, play a role. If I know how the I/O has to work, and I'm not building a "general-purpose" board, I'd probably use discrete (74xxx) logic or a programmable part, just because they cost less. If I wanted the flexibility that it offers, I might go with the 82C55, though.

RE