How to use Timer / Counter Overflow Interrupt in microcontroller

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In this tutorial we will learn how to use Timer / Counter Overflow Interrupt of PIC16F877A Microcontroller. Interrupt is most popular feature of any Microcontroller. PIC16F877A Microcontroller has 14 Interrupt sources.  You can watch the video or read the written tutorial below.

Interrupt
Interrupt is a signal Microcontroller emitted by hardware or software indicating and event that needs immediate attention .



PIC16F877A Microcontroller Interrupt list:

1. External Interrupt
2. RB Change Interrupt
3. Timer0 Interrupt
4. Timer1 Interrupt 
5. Parallel Slave Read / Write
6. A / D Converter Interrupt
7. USART Transmitter Interrupt
8. USART Receiver Interrup
9. USART Transmitter Interrupt
10. CCP1 Interrupt
11. CCP2 Interrupt
12. Comparator Interrupt
13. EEPROM Write Operation Interrupt
14. Bus Collision Interrupt

OPTION_REG Register and INTCON Register use for Interrupt control.

OPTION_REG Register

The OPTION_REG Register is a readable and writable register, which contains various control bits to configure the TMR0 Prescaler / WDT postscaler.

       OPTION_REG REGISTER

bit 7             RBPU: PORTB Pull-up Enable bit 

                    1 = PORTB pull-ups are disabled 

                    0 = PORTB pull-ups are enabled by individual port latch values 

bit 6             INTEDG: Interrupt Edge Select bit 

                   1 = Interrupt on rising edge of RB0/INT pin 

                   0 = Interrupt on falling edge of RB0/INT pin 

bit 5            T0CS: TMR0 Clock Source Select bit 

                   1 = Transition on RA4/T0CKI pin 

                   0 = Internal instruction cycle clock (CLKOUT) 

bit 4            T0SE: TMR0 Source Edge Select bit 

                   1 = Increment on high-to-low transition on RA4/T0CKI pin 

                   0 = Increment on low-to-high transition on RA4/T0CKI pin 

bit 3            PSA: Prescaler Assignment bit 

                   1 = Prescaler is assigned to the WDT  

                   0 = Prescaler is assigned to the Timer0 module 

bit 2-0        PS2:PS0: Prescaler Rate Select bits

INTCON Register

The OPTION_REG Register is a readable and writable register, which contains various enable and flag bits for TMR0 register Overflow, RB Port change and External RB0/INT pin Interrupts.

     INTCON REGISTER

bit 7           GIE: Global Interrupt Enable bit
                  1 = Enables all unmasked interrupts
                  0 = Disables all interrupts

bit 6           PEIE: Peripheral Interrupt Enable bit 
                  1 = Enables all unmasked peripheral interrupts
                  0 = Disables all peripheral interrupts

bit 5          T0IE: TMR0 Overflow Interrupt Enable bit
                 1 = Enables the TMR0 interrupt
                 0 = Disables the TMR0 interrupt

bit 4          INTE: RB0/INT External Interrupt Enable bit
                 1 = Enables the RB0/INT external interrupt
                 0 = Disables the RB0/INT external interrupt

bit 3           RBIE: RB Port Change Interrupt Enable bit
                  1 = Enables the RB port change interrupt
                  0 = Disables the RB port change interrupt

bit 2           T0IF: TMR0 Overflow Interrupt Flag bit
                  1 = TMR0 register has overflowed (must be cleared in software)
                  0 = TMR0 register did not overflow

bit 1           INTF: RB0/INT External Interrupt Flag bit
                  1 = The RB0/INT external interrupt occurred (must be cleared in software)
                  0 = The RB0/INT external interrupt did not occur

bit 0           RBIF: RB Port Change Interrupt Flag bit
                  1 = At least one of the RB7:RB4 pins changed state; a mismatch condition will continue                                      to  set the bit. Reading PORTB will end the mismatch condition and allow the bit to                                         be  cleared (must be cleared in software).
                  0 = None of the RB7:RB4 pins have changed state

CIRCUIT DIAGRAM FOR TIMER / COUNTER  INTERRUPT:

Mikro C Code For Timer/Counter Overflow Interrupt
void interrupt(){                      
     PORTB.F0 = 1;
     delay_ms(250);
     PORTB.F0 =0;
     T0IF_bit = 0;
     }
void main() {
     TRISB =0X00;
     PORTB = 0X00;
     TMR0 = 0;
     OPTION_REG = 0X07;
     INTCON = 0XA0;


}

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