Serin2 and Timer1

[retepsnikrep]

I'm confused now by the relationship between the crystal/int osc at 8mhz and the various clocks :?

So at 8mhz with Fosc/4 & 1/8 prescaler timer1 is ticking at 250,000hz? OK I get that.

But the sytem instruction clock is operating at? 8mhz instruction cycles a second or Fosc/4 = 2mhz? or something else?

[retepsnikrep]

The asm listing shows these instructions.

    MOVE?CT    000h, _T1CON??0
    MOVE?BB    TMR1H, _TMR1RunOn??HIGHBYTE
    MOVE?BB    TMR1L, _TMR1RunOn??LOWBYTE
    ADD?WWW    _PreLoad, _TMR1RunOn, _TMR1RunOn
    MOVE?BB    _TMR1RunOn??HIGHBYTE, TMR1H
    MOVE?BB    _TMR1RunOn??LOWBYTE, TMR1L
    MOVE?CT    000h, _PIR1??0
    MOVE?CT    001h, _T1CON??0

So how much to add to timer1 reload to compensate I wonder?
Looking at the data sheet these instructions all seem to need 1 cycle each? So I make that 8 cycles how much is that in TMR1 ticks?

[HenrikOlsson]

Hi,
You are correct, when using any other prescaler than 1:1 one instructioncycle is not equal to one timer tick.

If you're using 1:8 prescaler then the timer is incremented every 8th instructioncycle but it still doesn't matter if the Fosc is 8kHz or 8Mhz, the relationship between instructioncylce and timertick/count is still the same and that relationship is the prescaler ratio.

The problem with the ASM-listing that is generated is that it's not "true" ASM, those commands you have in your listing are macros which you then need to "expand" into the "real" ASM instructions. (Did you really find those instruction in the datasheet?) But if it does work out to 8 instructions and your prescaler is 1:8 then it equals exactly 1 timer tick.

/Henrik.