David,

This is a more detailed section of my code.
All code outside the interrupt routine finishes long before the next =
interrupt, and just hangs around a loop waiting, hence no need to store =
registers.

Running the code below works, just polling TMR1IF, and updates my =
display (shown in red)

If however I enable the code in blue (enabling interrupts) and comment =
out code in red, replacing it with a "loop goto loop" statement, my =
display is never updated (but should be if interrupts were being called)

ORG 0x000 ; processor reset vector
goto main ; go to beginning of program
ORG 0x004 ; interrupt vector location
;**********************************************************************
;interrupt routine here
;**********************************************************************
bank_low
CLRWDT
btfss PIR1,TMR1IF ;return if it wasn't a timer1 interrupt
retfie
movlw h'dc'
movwf TMR1L ;set timer1 to BDC, i.e. 3036 to give .5sec interval =
including prescaler
movlw h'0b'
movwf TMR1H
call updatedisplay

bcf PIR1,TMR1IF ;ensure interrupt flag is cleared ready for next =
interrupt

retfie
;**********************************************************************
;end of interrupt routine
;**********************************************************************
main clrf numL
clrf numH
clrf hund
clrf tens
clrf ones
clrf tens_ones
clrf secunit
clrf sectens
clrf minunit
clrf mintens
clrf PORTA
clrf PORTB
clrf PORTC
bank_high
movlw H'3F'
movwf TRISA ;all inputs
clrf TRISB ;all outputs
clrf TRISC ;all outputs
movlw b'10001000'
movwf OPTION_REG ;no pullups on port B, prescaler to WDT
movlw b'10000000' ;analogue conversion right justified, all inputs =
analogue
movwf ADCON1

bank_low
movlw b'01100001' ;Fosc/8, AN4, A/D on
movwf ADCON0
movlw b'00110000' ;set prescaler to 1:8
movwf T1CON
movlw h'dc'
movwf TMR1L ;set timer1 to BDC, i.e. 3036 to give .5sec interval =
including prescaler
movlw h'0b'
movwf TMR1H
bcf PIR1,TMR1IF ;ensure interrupt flag is clear

;movlw b'11000000' ;global interrupts, peripheral only
;movwf INTCON
;movlw b'00000001' ;Timer1 only
;movwf PIE1

bsf T1CON,TMR1ON ;enable timer1
call initdisplay
call home0
call stringcharge
movlw H'07'
call moveto0
call stringtime

loop btfsc PIR1,TMR1IF
call updatedisplay
bcf PIR1,TMR1IF ;ensure interrupt flag is clear=20
CLRWDT
goto loop

----- Original Message -----=20
From: David Cary=20
To: PICLIST@MITVMA.MIT.EDU=20
Sent: Tuesday, June 19, 2001 3:48 PM
Subject: Re: [PIC]: 16F876 Interrupts


  Dear Malcolm Peill,

  Malcolm Peill originally wrote:
  > bsf T1CON,TMR1ON ;enable timer1
  >
  >  call initdisplay
  >
  >I know the timer 1 overflow flag gets set, but never calls the =
interrupt =3D
  >vector.

  Malcolm Peill <Malcolm@PEILL.ORG.UK> on 2001-06-19 02:53:13 AM
  >My code is all in bank 0 and I don't need to save pclath, W reg, =
Status etc.
  >Thanks for the encouragement that the code seems to be ok. I'll have =
to keep
  trying.


  Sorry. Kneejerk reaction. At first glance, it looked like a common =
newbie
  mistake.

  I find it hard to believe that you don't need to save W, but if you =
say so ...

  The timer1 setup looks OK to me. Are you sure that the code that =
executes after
  you enable the timer (which you didn't post) doesn't disable the timer =
or its
  PIE interrupt enable bit or the INTCON interrupt enable bits ?

  --
  David Cary

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