PIC16F87 datasheet(138/230 Pages) MICROCHIP

138 / 230 page

PIC16F87/88

DS30487D-page 138

 2002-2013 Microchip Technology Inc.

FIGURE 15-6:

SLOW RISE TIME (MCLR TIED TO VDD THROUGH RC NETWORK)

15.10 Interrupts

The PIC16F87/88 has up to 12 sources of interrupt.

The Interrupt Control register (INTCON) records

individual interrupt requests in flag bits. It 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. When bit GIE is enabled and an

interrupt’s flag bit and mask bit are set, the interrupt will

vector

immediately. Individual

interrupts

can

disabled through their corresponding enable bits in

various registers. Individual interrupt bits are set

regardless of the status of the GIE bit. The GIE bit is

cleared on Reset.

The “return from interrupt” instruction, RETFIE, exits

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

re-enables interrupts.

The RB0/INT pin interrupt, the RB port change interrupt

and the TMR0 overflow interrupt flags are contained in

the INTCON register.

The peripheral interrupt flags are contained in the

Special Function Register, PIR1. The corresponding

interrupt enable bits are contained in Special Function

contained in Special Function Register, INTCON.

When an interrupt is serviced, the GIE bit is cleared to

disable any further interrupt, the return address is

pushed onto the stack and 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

software

before

re-enabling

interrupts

avoid

recursive interrupts.

For external interrupt events, such as the INT pin or

PORTB change interrupt, the interrupt latency will be

three or four instruction cycles. The exact latency

depends on when the interrupt event occurs, relative to

the current Q cycle. The latency is the same for one or

two cycle instructions. Individual interrupt flag bits are

set regardless of the status of their corresponding

mask bit, PEIE bit or the GIE bit.

VDD

MCLR

INTERNAL POR

PWRT TIME-OUT

OST TIME-OUT

INTERNAL RESET

TPWRT

TOST

Note:

Individual interrupt

flag bits

are

set

regardless

the

status

their

corresponding mask bit or the GIE bit.

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