> use timer 2 in time delay calculation

Are you still counting pulses per sec ?

Timer2 is an 8-bit timer, with a maximum 1:16 prescaler and a
maximum 1:16 postscaler. This makes it effectively a 16-bit
timer with upper byte resolution

If you want to time exactly one second then you'll have to work
out how many instruction cycles of your oscillator that will take

Assuming you use the full pre- and post- scalers, the simplest
way would be to choose a crystal that has a hex value and is
divisible by 256, as that will be the coarseness of Timer2

For example, say you choose 19.6608MHz, which is close to the
maximum speed of the 16F887

Fosc =3D 19.6608MHz, Fcy =3D 4.9152MHz. Divide by 256 (the
scaler count) and then divided by 256 (the TMR2 register count)
this equates to exactly 75 TMR2 interrupts per second

So, you set TMR2 to free-run, with no loading. Just let everything
roll over

Every time the postscaler rolls over, it generates a TMR2 interrupt.
In the ISR you increment a RAM register and test for 75. Or set
the RAM register to 75 and count down, testing for 0. Either way,
there's your second

If you choose a different crystal then obviously a different number
of interrupts per sec will be generated

A decimal crystal, such as 10.0000MHz, is going to require TMR2
reloads, because it is not exactly divisible by 2^x

Joe
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