... here I thought I'd understood what was going on ... silly me!

I figured it was HH:MM:SS since you had six switches. <sigh>

I haven't played chess in over a decade, except with my son, so I am not "up" on the latest trends.

There are still lots of options. You do have to settle, eventually, on a design, but looks to me as though you'd be better off, in terms of cost, etc, with a single MCU outside the 805x family, simply because of the lower cost of the high-pin-count parts and the availability of those parts in easy-to-prototype (without a PCB) packaging. There's a 68HC11 family member that comes in a 68-pin PLCC that has four ports AND an expanded data/address bus. That might be easier to use from a fabrication standpoint simply because you don't have to accomodate as many parts, AND because this part has a watchdog timer that will wake you up from a nap if you're saving power. I don't remember all the details. I bought a handfull of these a few months back just to have them around.

Without a doubt there's got to be a similarly packaged 805x family member, but you never know ...

I think, if you use the 4-1/2-digit multiplexed (multi-backplane) LCD's, you can get by with 15 pins or so per display. Displaytech will probably sample you a couple in a 30-pin package, od which half the pins are unused if you tell them what you are doing. If you read the switch pins at power-up using the same pins you'll ultimately use for LCD drive, you may be able to get by with that. The eight inputs from the switches won't be bothered by the signals you used to drive the data bits if you subsequently set them to be inputs, which, BTW, is not a factor with 805x's, IIRC. That way you can set the display for 1:59:59 to begin with or a greater value in hh:mm format, if you like. Multiplexing means your MCU has to be awake more of the time, but you can probably still have him sleeping most of the time.

When I think of a chess clock, I still think of one of those old mahogany or walnut wooden blocks with two backward-running alarm clocks in it, and two buttons on the top. I'm still having some trouble getting my mind around what you're wanting to do. Nonetheless, if you want, you can do this. With the muxed displays, and three 805x's or with a single MCU of some sort, it's all achievable. Remember, too, that you could use just one MCU to run two of the mux'd LCD's by muxing across all of the digits. That would just require an extra three pins, and you could have those available if you can get the multiplexed LCD type.

If you want to avoid external logic, the multi-MCU approach looks quite good, but a single MCU will use the least power. If you find a practical package with enough pins, that's the way to explore, since the pins don't affect power consumption very much at all unless they source or sink current. They're just a path to the rails, though they do have some resistance.

RE