There was a time (70's and '80's) when I used the 8048 quite a bit, and I don't remember any control registers. They didn't have SFR space, so you couldn't "talk" directly to I/O as memory, nor did they have bit-addressable registers. I don't remember much about variants, either. There was an 8048, and 8049, with twice as much memory, of both code and data space, and an 8050, with twice again as much (4KB code, 128 bytes data). Intel made 'em, and National, AMD, Signetics, a couple of Japanese manufacturers, and probably others I can't remember if I ever knew about them, did too.

The i804x series had I/O instructions, and, in fact, a couple of special ones to deal with their 8243 "Port Expander" IC.

I'm persuaded that the SFR concept is one of the things that made the 805x so much more convenient than the 804x. The fact that it was purported (in the marketing literature) to be "object code compatible" with the 804x didn't influence me at all, as it wasn't that "compatible."

RE