On Fri, Sep 01, 2023 at 04:32:57PM -0600, ben via cctalk wrote: [...] > I think that way has been for a while. Having a hard time finding a 68B50 > on ebay. All the modern serial devices (I can buy) seem to be serial > interfaced. Sigh.
I see the 68B50 on AliExpress, and they're probably even genuine. The vendor I'm tempted to order some other retro chips from offers them in five packs for about a euro each. For new parts available from a reputable supplier, there's the W65C51. The bumph notes it is "compatible with 65xx and 68xx microprocessors". Available in a variety of packages including DIP, and also in -S and -N variants depending on whether you want CMOS or TTL levels, it runs at a nominal 5V and has speed grades up to 14MHz. It's not a direct replacement for the 6850 but will look quite familiar and present no surprises. For new designs, it's simpler to use as it doesn't need external baud rate generators. A single W65C51N6TPG-14 (DIP, TTL, 14MHz) is €7.10 from my local Mouser. If you can handle SMD, there's even the venerable 16550 and clones which could be handy if you're trying to do high-speed serial, although that's got a more 8080-style bus interface so you'll need a few extra gates to get that going. > PS: Is it me or was the 6850 ACIA the only simple and bug free uart around > at the time with interupts. The W65C51 datasheet notes it has a bug with the flag bit indicating that the transmit buffer is empty, and the recommended workarounds are "don't do that" or "keep using the old NMOS 6551". I suggest the former since the latter is probably once again harder to find.
