> (and 'soft stop'?)

Wouldn't worry about that

> I intend to use an ISR to generate a tick perhaps every 250 usecs

250us @ 20MHz is over 600 instruction cycles. Plenty, I'd have
thought, with 25,000 (10ms) IC between zero-crossing points

I recall a suggestion that slices of 100us works well but 250us
would be OK for just ramp-up from off to on. Even after 9 updates
there's still 8ms until the next z-c

How are you doing the z-c detection btw ?

> b) debounce PBs by reference to ticks

You could add an RC to lessen/eliminate switch noise and use a
shorter switch debounce routine. Choosing a classy pushbutton
pays off too

It doesn't sound like the PIC would have too much trouble supervising
a circuit like that. Some paperwork and a flow diagram for the code
beforehand wouldn't be a bad idea, to get all the timing nicely dove-
tailed

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