> What I'm trying to do is creating 1s interrupt on the background
> with Timer0, I have set Timer0 to B2 and I need a counter for it

First you need to do some maths .......

20MHz crystal =3D 5MHz execution frequency

Therefore you need to have a counter for 5,000,000 cycles for 1s
or 5000 cycles for 1ms

Assuming you don't use a 1:64 scaler -

The interrupt can include a conditional, so that it processes Timer0
IRQs as well as does what you want after 1s

For example, a 1ms interrupt counter done 1000 times

5000/256 =3D 19.53125, ie 19 counts of 0-255 and 1 of 136

Load Timer0 with 120 (ie -136)
Load counter1 with 20
Load counter2 with 0x18 (low byte of -1000)
Load counter3 with 0xfc (high byte of -1000)
Enable Timer0 interrupts
Start Timer0

In the ISR, something like this (untested)

Note that loading Timer0 whilst it is running introduces jitter. That
is, I think, you may need to reload with 122 rather than 120 because
the decfsz has taken 2 cycles (it's late and I've done enough thinking
today  ;-)) )

      decfsz counter1 ;count Timer0 interrupts
      goto exit ;not finished
      movlw .120 ;reload Timer0
      movwf timer0
      clrf counter1 ;reset rollover counter

;count from -1000 to 0

      incfsz counter2 ;increment low counter
      goto exit ;<> 0
      incfsz counter3 ;increment high counter
      goto exit ;<> 0

;both counter2 and counter3 are 00

      movlw 0x18 ;reload 1000 counter
      movwf counter2
      movlw 0xfc
      movwf counter3

      do the 1s thing

exit retfie

The first time through, the 136 is taken care of, then another 19
counts of 256, until counter1 =3D 0, looped 1000 times until counters
2 and 3 are 0, the 1s thing is done and the whole loop starts again

Substitute -100 or -10 for 100ms and 10ms etc

If you use a 19.660800MHz crystal then you can simply let Timer0
run without reloading, because 19660800 is divisible evenly by 256
and more

19.660800/4 =3D 4.915200MHz execution frequency

4915200 / 256 =3D 19200, 19200 / 64 =3D 300
4915200 / 65536 =3D 75

Joe
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