PIC16F676-ESLASHST datasheet(65/132 Pages) MICROCHIP

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DS40039F-page 65

PIC16F630/676

9.4

Interrupts

The PIC16F630/676 has 7 sources of interrupt:

• External Interrupt RA2/INT

• TMR0 Overflow Interrupt

• PORTA Change Interrupts

• Comparator Interrupt

• A/D Interrupt (PIC16F676 only)

• TMR1 Overflow Interrupt

• EEPROM Data Write Interrupt

The Interrupt Control register (INTCON) and Peripheral

Interrupt register (PIR) record individual interrupt

requests in flag bits. The INTCON register also has

individual and Global Interrupt Enable bits.

A Global Interrupt Enable bit, GIE (INTCON<7>)

enables (if set) all unmasked interrupts, or disables (if

cleared) all interrupts. Individual interrupts can be

disabled through their corresponding enable bits in

INTCON register and PIE register. GIE is cleared on

Reset.

The return from interrupt instruction, RETFIE, exits

interrupt routine, as well as sets the GIE bit, which re-

enables unmasked interrupts.

The following interrupt flags are contained in the

INTCON register:

• INT pin interrupt

• PORTA change interrupt

• TMR0 overflow interrupt

The peripheral interrupt flags are contained in the

special register PIR1. The corresponding interrupt

enable bit is contained in Special Register PIE1.

The following interrupt flags are contained in the PIR

• EEPROM data write interrupt

• A/D interrupt

• Comparator interrupt

• Timer1 overflow interrupt

When an interrupt is serviced:

• The GIE is cleared to disable any further interrupt

• The return address is pushed onto the stack

• The PC is loaded with 0004h

Once in the Interrupt Service Routine, the source(s) of

the interrupt can be determined by polling the interrupt

flag bits. The interrupt flag bit(s) must be cleared in soft-

ware before re-enabling interrupts to avoid RA2/INT

recursive interrupts.

For external interrupt events, such as the INT pin, or

PORTA change interrupt, the interrupt latency will be

three or four instruction cycles. The exact latency

depends upon when the interrupt event occurs (see

Figure 9-11). The latency is the same for one or two-

cycle instructions. Once in the Interrupt Service

Routine, the source(s) of the interrupt can be

determined by polling the interrupt flag bits. The

interrupt flag bit(s) must be cleared in software before

re-enabling interrupts to avoid multiple interrupt

requests.

Note 1: Individual interrupt flag bits are set,

regardless

the

status

their

corresponding mask bit or the GIE bit.

2: When an instruction that clears the GIE

bit is executed, any interrupts that were

pending for execution in the next cycle

are ignored. The interrupts which were

ignored are still pending to be serviced

when the GIE bit is set again.

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