Alan B. Pearce wrote:

>> Thanks for the idea of subtracting to set Timer 1. I know about testing
>> the lsb of the timer, and I see how subtracting would also work.
> 
> You don't need to do any special subtracting with timer 1. Remember that the
> timer counts from the value you load down to 0, and then when counting from
> 0 to -1 it sets the timer 1 flag that can generate the interrupt, when the
> interrupt flag is enabled. Each clock cycle will count further in the
> negative direction, so by the time you service the timer it might have
> reached -8 to -10. Now the trick is not to load the timer with the count
> value, but to ADD the count value to the negative value in the timer. 

Hmm... When I was suggesting subtracting the period count, I was assuming
that timer 1 /increments/ and that the timer flag gets set when it rolls
over from 0x0000 to 0xffff. At least that's what my (possibly failing :)
memory tells me.

This provides the same mechanism you are describing, but with a subtraction
instead of an addition.

Gerhard

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