Joe,
     I check and mouser stocks 19.6608MHz crystals. They are 0.39 each.=20
I can do that. I could place an order with them for the crystal and a=20
few other things so as to spread out the cost of shipping. But I could=20
use this for right now with the 20MHz crystal. Could you please send me=20
the code to do it the other way?
Thanks,
rich!

On 7/18/2014 4:57 AM, IVP wrote:
>>      This is what I don't know how to do
> Using TMR1 is very simple (when you know how to do it)
>
> Here are some jottings. E&OE. Watch the banking, I didn't look
> any up for this so you may need more or fewer banksels. The aim
> is for the IRQ system to be reset after the 76th interrupt. As I
> mentioned, the '19264' will need to be decreased by the number
> of cycles needed to do the load. TMR1 can be stopped during
> the load and restarted after, remember to take those instruction
> cycles into account as well
>
> Note that if a 19.6608MHz had been used the ISR would have
> been quite a bit simpler, just a 75 count
>
> The timing system could be done quite a different way. For example
> load TMR1 with 50,000 (-ish) every time and count 100 interrupts
> to get the 5,000,000. This does give you some consistency of
> execution in the ISR as there's no clean-up 77th interrupt
>
> Joe
>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
> ;make a flag in a RAM location
>
> #define  last_irq  flags,0
>
> ;configure TMR1
>
>           banksel t1con
>           movlw   b'00000000'
> ;                  -
> ;                   0           not T1osc
> ;                    00         pre-scaler =3D 1:1
> ;                      0        T1osc off
> ;                       0       internal source
> ;                        0      internal source
> ;                         0     T1 off
>           movwf   t1con
>
> ;initialise interrupt counter to - 76
>
>           banksel irqs
>           movlw   -.76
>           movwf   irqs
>           bcf     last_irq       ;initialise "last interrupt" flag
>
> ;enable TMR1 interrupts
>
>           banksel pie1
>           bsf     pie1,tmr1ie
>           bsf     intcon,peie
>           bsf     intcon,gie
>
>           clrf    tmr1l
>           clrf    tmr1h
>
>           bsf     t1con,tmr1on  ;start TMR1
>
> here   goto   here
>
> ;=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
> ;ISR
>
> irq      bcf     pir1,tmr1if    ;clear irq flag
>           btfsc   last_irq       ;test if last interrupt
>           goto    last           ;yes
>
>           incfsz  irqs           ;increment, skip after 76 interrupts
>           retfie                 ;exit
>
>           banksel tmr1l
>           movlw   low(.19264)    ;load TMR1 for last interrupt period
>           movwf   tmr1l
>           banksel tmr1h
>           movlw   high(.19264)
>           movwf   tmr1h
>
>           banksel flags
>           bsf     last          ;set "last interrupt" flag
>           retfie                ;exit
>
> last    banksel  irqs
>           movlw   -.76          ;re-initialise counter
>           movwf   irqs
>           bcf     last_irq       ;and "last interrupt" flag
>
>           movf    portb,w       ;read portb
>           xorlw   b'00000001'   ;toggle portb,0
>           movwf   portb         ;write portb
>          =20
>           retfie                ;exit

--=20
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