As many people have done, I've used 'em both. Having started out with the i8048, I was interested in the i805x, but found it wanting next to the then-popular 6801, which has long been replaced by the 68HC11 family. For every 805x app I've worked through, I've had a dozen 6801, 05, HC05, HC11, etc, and I like very much that they've had similar architecture and assembly language, with slight variations throughout. The 68HC05's lacked the double accumulator (concatenated A and B registers, that the '01, and 'HC11 have and the the Y index register that the 'HC11 offers. Until the evolution of the DS89C4x0 series from Dallas and later Maxim, I had essentially no interest in the 805x core because, function for function, it was less thrifty to use than the MOTOROLA types, not to mention that the MOT types outperformed price-comparable 805x types by quite a bit.

That situation doesn't apply to the latest versions, though, and the MOT types aren't appearing as free IP cores, which indicates they're probably not as popular any longer. The MOT parts don't seem to have many second sources as they once did, though the 805x parts don't either.

If the 'HC05C8, which was obsolted over a decade ago, being replaced with an HC05A part that was twice as fast, was adequate, then it's likely nearly any microcontroller can do the job as it stands. If you want better performance, I have little doubt that the DS89C4x0's which don't cost appreciably more than the low-end MOT controllers, in similarly low volume, would be very much a better choice as it is so MUCH faster and has much more capability to store accumulated samples, as well as having two serial ports and 1 KB of extra internal SRAM and between twice and four times as much code storage.

RE