example of using TMR0 interrupt

[kichapi]

interrupt

how to configer interrupt function?i used 16f877a pic and how to calculate TMR0? please help me?

 

[JoKKeR]

Re: interrupt

Hi,

It could be very useful to know compiler, your using.

The theory is.

(from data sheet you can find x register address and value)
-Enable global interrupt
-Enable interrupt on timer 0 overflow
also you may need to configure timer (clock, 8 or 16 bit, clock division )

To execute interrupt function you need add interrupt name (which compiler are you using) and under it you can add function to execute. Example #TIMER0_INT

 

[Tahmid]

interrupt

Hi kichapi,
Here I post an example of using TMR0 interrupt:
[Code written in Microchip ASM]

	LIST P=16F877A
	__CONFIG _CP_OFF & _DEBUG_OFF & _WRT_OFF & _LVP_OFF & _CPD_OFF & _BODEN_OFF & _PWRTE_OFF & _WDT_OFF & _XT_OSC

	#INCLUDE <P16F877A.INC>
	
	CBLOCK 0x20
		COUNT, PCOUNT
	ENDC

	ORG 0x00
	GOTO MAIN

	ORG 0x04 ;INTERRUPT VECTOR
	GOTO ISR ;INTERRUPT SERVICE ROUTINE
;================================================

ISR
	INCF	COUNT ;INCREMENT CONTENTS OF COUNT
	MOVF	COUNT, W ;MOVE COUNT TO W
	BTFSC	STATUS, Z ;CHECK IF COUNT = 0
	;COUNT = 0, WHEN COUNT INCREMENTS AND OVERFLOWS AT ROLLOVER
	;	FROM 255 TO 0
	INCF	PCOUNT ;EVERY OVERFLOW OF COUNT, INCREMENT CONTENTS
	;OF PCOUNT
	MOVF	PCOUNT, W ;MOVE CONTENTS OF PCOUNT TO W
	MOVWF	PORTB ;MOVE CONTENTS OF W TO PORTB
	BANKSEL	INTCON ;BANK0
	BCF		INTCON, TMR0IF ;CLEAR INTERRUPT FLAG
RETFIE
;================================================

MAIN
	BSF		COUNT, 1 ;COUNT = 1
	CLRF	CCP1CON ;CCP OFF
	BANKSEL	TRISB ;BANK1
	CLRF	TRISB ;ALL OUTPUT
	MOVLW	.7
	MOVWF	CMCON ;COMPARATOR OFF
	MOVWF	ADCON1 ;ADC OFF
	MOVLW	0x82
	MOVWF	OPTION_REG ;PORTB PULL-UP OFF, PRESCALER- 1:8
	BANKSEL	INTCON ;BANK2
	MOVLW	0xA0
	MOVWF	INTCON ;Global interrupt and TMR0 interrupt enabled
	CLRF	PORTB ;CLEAR PORTB
	BANKSEL	TMR0 ;BANK0
	CLRF	TMR0 ;RESTART TMR0
	GOTO	$ ;WAIT FOR INTERRUPT
END
;==================================================

I have commented so that you understand what happens. Every instruction = 1/ (4MHz/4) = 1us
Every (8 * 256) [8 because of prescaler] instructions, interrupt occurs, so interrupt occurs every 2.048 ms. Every (2.048 * 256)ms PCount increments. So PORTB value is incremented every 524ms. Try it out yourself.

Added after 7 minutes:

Same thing in mikroBASIC:

program TMR0INTEDA

dim COUNT as byte
dim PCOUNT as byte

sub procedure interrupt
    inc(COUNT)
    if (COUNT = 0) then
       inc(PCOUNT)
    end if
    PORTB = PCOUNT
    INTCON.TMR0IF = 0
end sub

main:
     COUNT = 1
     CCP1CON = 0
     TRISB = 0
     CMCON = 7
     ADCON1 = 7
     OPTION_REG = 0x82
     INTCON = 0xA0
     PORTB = 0
     TMR0 = 0
     while true
     wend
end.

 

[muhammadazhar]

Dear I am working in one project where I need to get pulses on RA4 of 16F877, I am unable to do so, see if you can help me. I just need to get the pulses and display on LCD. I have uploaded all of my code at

www.evsoft.pk/azhar/Pulses.rar

Thanks in Advance.

-Azhar