True enough, Neil, however ...

It might, actually, be cheaper, at least from the standpoint of getting something "out the door," to use separate MCU's.

It's all a matter of priorities. If Peter wants to "get-er-done," he may choose to go one way, and if he's interested in the most elegant, efficient, and cost-effective solution, he may choose differently.

I suspect he'll have a difficult enough time finding a source of 7-segment LC "clock" displays packaged such that he can easily use them. Once he has 'em he has to figure out how, exactly to drive them, together with those switches he has to handle. Once he's done that, he has to count pins, calculate power, etc, and only then can he reasonably make a decision about what actual hardware he'll use.

One choice might be to drive each display with a 40-pin 805x, using the three pins that remain for a comm link. He can then use his smaller MCU to deal with the switches if there are enough pins left to communicate the result, after which the thing can go to sleep. The fact is, however, that there are lots of available choices, and Peter has to decide which set suits him.

RE