[stoppingin]

Apologies for a silly question, what exactly are we looking at here? I've seen the inside of an F-91W, and I always imagined that under the black epoxy blob was some kind of off-the-shelf microprocessor (most likely 4-bit) with a mask ROM containing the watch's logic. Is the entire watch run from this IC, with no processor? If so that's really interesting.

[SnowHill9902]

If you are making millions of units for a RT application you definitely want custom silicon.

[stoppingin]

Is this on account of cost, or simplifying verification? I was under the impression that minimising the overall risk of a design was a major consideration. I'd love to know more about how these design decisions were made.

[BarsMonster]

Power consumption and cost. 10 years on a battery is very hard to achieve for microcontroller.

https://sorwatch.net shows that : with much more advanced microcontroller (much more modern tech.node, low power features) - it only works for 1-2 years on a single battery after extensive power optimizations.

In custom silicon when seconds tick - it's maybe 100 transistors change their state. In microcontroller - it's roughly 10'000-100'000 transistors changing state to handle interrupt and update display content...