PIC876 datasheet(131/218 Pages) MICROCHIP

131 / 218 page

 2001 Microchip Technology Inc.

DS30292C-page 129

PIC16F87X

12.10 Interrupts

The PIC16F87X family has up to 14 sources of inter-

rupt. The interrupt control register (INTCON) records

individual interrupt requests in flag bits. It also has indi-

vidual 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 be dis-

abled through their corresponding enable bits in vari-

ous

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 inter-

rupt, and the TMR0 overflow interrupt flags are con-

tained in the INTCON register.

The peripheral interrupt flags are contained in the spe-

cial function registers, PIR1 and PIR2. The correspond-

ing interrupt enable bits are contained in special

function registers, PIE1 and PIE2, and the peripheral

interrupt enable bit is contained in special function reg-

ister INTCON.

When an interrupt is responded to, 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 to

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 when the interrupt event occurs. 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 GIE bit.

FIGURE 12-9:

INTERRUPT LOGIC

Note:

Individual interrupt flag bits are set, regard-

less of the status of their corresponding

mask bit, or the GIE bit.

PSPIF

PSPIE

ADIF

ADIE

RCIF

RCIE

TXIF

TXIE

SSPIF

SSPIE

CCP1IF

CCP1IE

TMR2IF

TMR2IE

TMR1IF

TMR1IE

T0IF

T0IE

INTF

INTE

RBIF

RBIE

GIE

PEIE

Wake-up (If in SLEEP mode)

Interrupt to CPU

CCP2IE

CCP2IF

The following table shows which devices have which interrupts.

Device

T0IF INTF RBIF PSPIF ADIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF EEIF BCLIF CCP2IF

PIC16F876/873

Yes

—

Yes

PIC16F877/874

Yes

BCLIE

BCLIF

EEIF

EEIE

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