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PICList Thread
'help wanted!'
1998\01\25@174816 by Jack Raats

1998\01\26@065332 by Caisson

> Van: Jack Raats <spam_OUTjackTakeThisOuTJARASOFT.XS4ALL.NL>
> Aan: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU
> Onderwerp: help wanted!
> Datum: zondag 25 januari 1998 23:28
>
> I have to write code in which I've to wait minutes. Is it possible to
> use the TIMER0 (TMR0) module to generate such delays?

IF your TIMER0 has an big enough resolution _and_ IF your clock goes slow
enough
it could work ....  :-)

Generaly you mak a setup for the longest wait-time of your TIMER0, and than
create a software-counter on-interrupt (which functions as a extention of
the
hardware-timers).  than let the software-counter set a flag when it
expires.

> If so could anyone send me some source code for example?

The below code is for a PIC16C74, it does not go for the longest
delay-time, but it's only an example ...


;----------------------------

               org Interrupt

;----------------------------
;Because W-register is saved before the Bank-select bits are set for the
Interrupt-routine
;the register-bank in wich the W-register is saved is undetermined.
therefore the Storage-
;register S_WReg exists in _ALL_ register-banks !

               movwf   S_WReg          ;Save W register
                                               ;/ ! S_WReg exists in _ALL_ regi
ster-banks !
               swapf   STATUS,W                ;Save Status register
               bcf     STATUS,RP0              ;/ Select Register-bank #0
               movwf   S_SReg          ;/

               btfsc   PIR1,TMR1IF             ;Call Timer 1 routine
               call    I_Timer                 ;/ on interrupt

               swapf   S_SReg,W                ;Restore Status register
               movwf   STATUS          ;/
               swapf   S_WReg          ;Restore W register
               swapf   S_WReg,W                ;/
               retfie

;----------------------------

;----------------------------
; Initialize Timer #1

InitTimer:      clrf    TMR1L           ;Clear timer #1
               clrf    TMR1H           ;/

               movlw   B'00000001'     ;Initialize Timer #1
               movwf   T1CON           ;/

               bsf     STATUS,RP0      ;Switch to Bank #1
               bsf     PIE1,TMR1IE     ;Enable Timer #1 interrupt
               bcf     STATUS,RP0      ;Switch to Bank #0

               movlw   b'11000000'     ;Enable global & peripheral
               iorwf   INTCON          ;/ interrupts

               return

;----------------------------

I_Timer:                movlw   low  -10000     ;Re-Load timer
               movwf   TMR1L           ;/ (+/- 100 Int's @ a 4MHz crystal)
               movlw   High -10000     ;/
               movwf   TMR1H           ;/

               bcf     PIR1,TMR1IF     ;Clear Interrupt-flag

               decfsz  SoftDelay       ;Return if Software delay not done
               return                  ;/

               movlw   0x??            ;re-Load software counter
               movwf   SoftDelay       ;/

               bsf     DelayDone,0     ;Set flag to indicate that the delay has
expired

               return

;----------------------------


> With greetings ... Jack Raats

Greetz,
  Rudy Wieser

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