Knowing pic16f877 Interrupt Registers

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INTERRUPTS IN 16F877A

The interrupt sources in PIC can be broadly classified into .
1.External interrupt
2.Internal interrupts .

There are totally 14 sources of interrupts in PIC16F877A .

1. Timer0 overflow interrupt
2. Timer 1 interrupt
   
3. Timer 2 interrupt
   
4. Capture compare interrupt ccp1.
5. Capture compare interrupt ccp2.
6. Comparator Interrupt
   
7. USART Transmitter interrupt
   
8. USART Receiver Interrupt
   
9. Synchronous Serial Port interrupt
   
10. EEPROM Write Interrupt
    
11. Analog to Digital Converter interrupt
    
12. Parallel slave port read write interrupt
    
13. Bus collision interrupt
    
14. External interrupt (RB0/INT0)

Starting with the registers .
The global register for the interrrupt is INTCON .The following tables show you the individual bits .

GIE

PEIE

TOIE

INTE

RBIE

TOIF

INTF

RBIF

The description of the individual bits are given below .The status of different interrupts when set as o and 1 .

BIT	NAME	WHEN SET 1	WHEN SET O
GIE	Global interrupt bit	Enable all	Disable all
PEIE	Peripheral interrupt enable bit	Enable all unmaskable peripheral interrupts	Disable all peripheral interrupts
TOIE	Timer 0 overflow interrupt enable bit	Enable	Disable
INTE	RB0/INT external interrupt enable bit	Enable	Disable
RBIE	RB port change interrupt enable bit	Enable	Disable
TOIF	Timer 0 overflow interrupt flag	TMR0 reg overflows
INTF	RB0/INT external interrupt flag	External interrupt occurs	No interrupt
RBIF	RB port change interrupt flag bit	One line changes its state from RB7 to RB4	No line changes

The first five bits are configuration bits and the next 3 lower bits are FLAGS .That will be set as 1 when the corresponding interrupt occours .It is the programmers responsiblity to clear those bits .It wont be cleared automatically .Its for the reson because if another interrupt occours while processing the previous interrupt it will lead to chaos .So the task is given to the programmer to clear the bits .

In addition to INTCON reg peripheral interrupt also has 4 more reg PIE1 , PIE2 corresponding to PIEX and PIR1 and PIR2 coressponding to PIRX.Let us see these registers in the next tutorials .

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