PIC16F877A - Timer0 won't interrupt

[WishMaster^]

Hello all,

I've been struggling with a, for a not-picbasic-newbie (which I am! ), simple problem. I'm trying to let a LED blink on the overflow rate of timer0. Unfortunately I wasn't very succesfull.

When I run the following code (I know the LED won't blink with this, but that's step 2)

define loader_used 1  
define osc 20        

led var portc.1            ;LED is connected on PortC.1

wsave var   byte $20 system
ssave var   byte bank0 system
psave var   byte bank0 system

Goto main

define INTHAND tmroverflow

asm
tmroverflow movwf	wsave
            swapf	STATUS, W
            clrf	STATUS
            movwf	ssave              ;Interrupt
            movf	PCLATH, W          ;Routine
            movwf	psave              ;with Save function
                                       
            bsf     _led               ;Put on LED  
            
            movf	psave, W
            movwf	PCLATH
            swapf	ssave, W
            movwf	STATUS
            swapf	wsave, F
            swapf	wsave, W
            
            bcf     intcon,2           ;Clear Interrupt Flag
            
            retfie
ENDASM

main:
   INTCON = %10100000                  ;GIE enabled, T0IE enabled
   OPTION_REG = %00000101              ;Prescaler on TMR0 rate 1:32
   goto loop
   
loop:
   goto loop                           ;Wait here for interrupt

When I run it in debug mode, the compiler goes insane and gives me mismatched address errors after the timer didn't respond for some time (the watchdog timer is off, so it isn't him who's complaining )
I think that my mistake is in the INTCON and/or the OPTION_REG, but experimenting with this values didn't helped me further neither.
The "save" function is O.K asfar as I can see, since it's straight out of the manual!!

All it need to do for step 1 is to light the LED...

So if someone sees the problem right away, and I'm sure there will be many, please help this desperate newbie! I will be very gratefull!

Cheers,

William

[skimask]

I don't see anything for a TRISC.1 = 0

[skimask]

define loader_used 1  
define osc 20        

led var portc.1            ;LED is connected on PortC.1
ledcnt var word

wsave var   byte $20 system
ssave var   byte bank0 system
psave var   byte bank0 system

Goto main

define INTHAND tmroverflow

asm
tmroverflow movwf	wsave
            swapf	STATUS, W
            clrf	STATUS
            movwf	ssave              ;Interrupt
            movf	PCLATH, W          ;Routine
            movwf	psave              ;with Save function
                                       
            inc          _ledcnt            ;increment the counter
            
            movf	psave, W
            movwf	PCLATH
            swapf	ssave, W
            movwf	STATUS
            swapf	wsave, F
            swapf	wsave, W
            
            bcf     intcon,2           ;Clear Interrupt Flag
            
            retfie
ENDASM

main:
   INTCON = %10100000                  ;GIE enabled, T0IE enabled
   OPTION_REG = %00000101              ;Prescaler on TMR0 rate 1:32
   Output LED
   
loop:
   led = ledcnt.7                     ;make the led follow bit 7 of ledcounter
   goto loop                           ;Wait here for interrupt

A couple of changes. If you don't see the LED blink, turn up the prescaler and/or use a slower oscillator for test. At least you should see it work.

[sougata]

[code]


incf _ledcnt ;increment the counter

Hi,

Skimask I think it should be incf and is a simple typo.

[skimask]

Hi,

Skimask I think it should be incf and is a simple typo.

Yep, should be, and is......then again, it is Friday the 13th....maybe my keyboard is playing em no skcirt

[Darrel Taylor]

Interrupts and the MSC Debugger don't get along very well together.

You must DISABLE debugging in any interrupt routines.

DISABLE DEBUG
asm
tmroverflow movwf	wsave
    ...
    ...
            retfie
ENDASM
ENABLE DEBUG

For an 877, you should use $70 for the wsave address.

OPTION_REG = %00000101 sets the prescaler to 1:64. (comment says 32)

and, like skimask said ... set the LED's pin to output.

[paul borgmeier]

Also a working example on MELABs website
http://www.melabs.com/resources/samples/pbp/asmint.bas
(maybe you got your start for yours there? I did not check if they are similar)