Joe,
     Wow, that is a big difference in code. I just ran the numbers=20
because I wanted to see what would happen using this code with a 20MHz=20
clock and the error is almost 2 percent. But I could use that until I=20
receive the other crystal. Hum, I'll trying coding these later on today=20
or sometime tomorrow.
Thanks,
rich!

On 7/18/2014 5:40 AM, IVP wrote:
>> Could you please send me the code to do it the other way?

> E&OE
>
> PS best practice is to save and restore W and STATUS, as they will
> probably be altered by the ISR. This could affect operation when you
> return to the main code
>
> Here's how to, from the 628 datasheet. Although note that BCF
> STATUS,RP0 does not guarantee Bank0. banksel status_temp
> is much better, if indeed Bank0 is where you assigned the temporary
> storage to be in
>
> So, have a couple of registers w_temp and status_temp in Bank0
> RAM. Microchip's comments below are not clear or complete. You
> may be in Bank1 when the ISR is entered, and so W may be stored
> in completely the wrong RAM. Make sure W and STATUS are
> being saved and recalled from the correct bank. Any bank, as long
> as it's the right one and W and STATUS are as they were when
> the main code was left
>
> MOVWF W_TEMP ;copy W to temp register,
> ;could be in either bank
> SWAPF STATUS,W ;swap status to be saved into W
> BCF STATUS,RP0 ;change to bank 0 regardless
> ;of current bank
> MOVWF STATUS_TEMP ;save status to bank 0
> ;register
> :
> : (ISR)
> :
> SWAPF STATUS_TEMP,W ;swap STATUS_TEMP register
> ;into W, sets bank to original
> ;state
> MOVWF STATUS ;move W into STATUS register
> SWAPF W_TEMP,F ;swap W_TEMP
> SWAPF W_TEMP,W ;swap W_TEMP into W
>
> Joe
>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
> ;iinitialise IRQ counter
>
>            movlw   -.75
>            movwf   irqs
>
> ;ISR
>
> irq      bcf     pir1,tmr1if    ;clear irq flag
>
>            incfsz  irqs           ;increment, skip after 75 interrupts
>            retfie                 ;exit
>
>            movlw   -.75          ;re-initialise counter
>            movwf   irqs
>
>            movf    portb,w       ;read portb
>            xorlw   b'00000001'   ;toggle portb,0
>            movwf   portb         ;write portb
>
>            retfie                 ;exit

--=20
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