Post by thread:[PIC]: 16F876 Interrupts

Can anyone advise me on what I'm missing in getting interrupts to work using the timer1 overflow on the 16F876. I have to admit to never having used interrupts before, so it may be obvious to those who have..... My code includes the following: ORG 0x000 ; processor reset vector goto main ; go to beginning of program ORG 0x004 ; interrupt vector location 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 letters ;rest of handler here bcf PIR1,TMR1IF retfie ;end of interrupt routine ;********************************************************************** main ; ;other code here 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 I know the timer 1 overflow flag gets set, but never calls the interrupt vector. Any help greatly appreciated. Malcolm. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Dear Malcolm Peill, Malcolm Peill <spam_OUTMalcolmTakeThisOuTPEILL.ORG.UK> on 2001-06-18 11:04:51 AM admitted a lack of knowledge when he said: {Quote hidden}>I have to admit to never having used interrupts before, so it may be obvious >to those who have..... > >My code includes the following: > > ORG 0x000 ; processor reset vector > goto main ; go to beginning of program > ORG 0x004 ; interrupt vector location > > bank_low > CLRWDT > btfss PIR1,TMR1IF ;return if it wasn't a timer1 interrupt Yes, it's obvious. Interrupt routines need to save all kinds of stuff at the beginning of the interrupt routine, then restore them at the end of the routine. It's a little tricky, so everyone starts with the code in the _PIC16F87X data sheet_ by Microchip Technology Inc. http://www.microchip.com/0/lit/pline/picmicro/ p. 132: Example 12-1: Saving Status, W, and PCLatH Registers . Also be sure to use piclist.org/techref/microchip/isrregs.htm for a few improvements. -- David Cary -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

David, This is not always needed. You only have to "save all kinds of stuff" if it is needed to be saved. I have MANY times had a simple little program where my code went something like: Main btfss TMR_F goto Main bcf TMR_F ...... goto Main All my interupt routine does is set TMR_F. I then waste time in the first two lines of my code waiting for the timer to overflow. I don't care about saving anything cause I start everything over again after the interrupt. I will state AGAIN what his request was. His request was not how does he handle the internals of the interupt routine. His request was how does he get the interupt routine to execute. Or to put it in his own words, "...the timer 1 overflow flag gets set, but never calls the interrupt vector." David, On the other side of the arguement, you are correct that he should at least be aware that certain values MAY need to be saved. I know that when I first started, this gave me headaches also. Malcolm, Assuming that your problem is not saving certain registers but is indeed as you stated, "...the timer 1 overflow flag gets set, but never calls the interrupt vector" all I can say is that I can't find anything wrong with it. Then again, I can't see the nose on my face sometimes either. David Cary wrote: {Quote hidden}> Dear Malcolm Peill, > > Malcolm Peill <.....MalcolmKILLspam@spam@PEILL.ORG.UK> on 2001-06-18 11:04:51 AM admitted a lack > of knowledge when he said: > >I have to admit to never having used interrupts before, so it may be obvious > >to those who have..... > > > >My code includes the following: > > > > ORG 0x000 ; processor reset vector > > goto main ; go to beginning of program > > ORG 0x004 ; interrupt vector location > > > > bank_low > > CLRWDT > > btfss PIR1,TMR1IF ;return if it wasn't a timer1 interrupt > > Yes, it's obvious. Interrupt routines need to save all kinds of stuff at the > beginning of the interrupt routine, then restore them at the end of the routine. > It's a little tricky, so everyone starts with the code in the > _PIC16F87X data sheet_ by Microchip Technology Inc. > http://www.microchip.com/0/lit/pline/picmicro/ > p. 132: Example 12-1: Saving Status, W, and PCLatH Registers > . > Also be sure to use > piclist.org/techref/microchip/isrregs.htm > for a few improvements. > > -- > David Cary > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

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 = >vector. Malcolm Peill <MalcolmKILLspamPEILL.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 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

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 CLRWDT goto loop {Original Message removed}

Malcolm Peill wrote: > > 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) This does not clear the WDT... Loop goto Loop Loop clrwdt goto Loop You say that the TMR1 interval is 0.5S which may be causing WDT resets. > i.e. 3036 to give .5sec interval including prescaler As you say you don't need to save W etc in your ISR in this case, but you do if you enable the other section of your main code because W and STATUS may be changing.... > call updatedisplay Does this subroutine take longer to execute than the WDT period? -- Best regards Tony mICros http://www.bubblesoftonline.com EraseMEsalesspam_OUTTakeThisOuTbubblesoftonline.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body