PIC16F87 Datasheet, PDF (140/214 Pages) Microchip Technology – 18/20/28-Pin Enhanced FLASH Microcontrollers with nanoWatt Technology

PIC16F87/88
FIGURE 15-6:
SLOW RISE TIME (MCLR TIED TO VDD THROUGH RC NETWORK)
5V
VDD
0V
1V
MCLR
INTERNAL POR
PWRT TIME-OUT
OST TIME-OUT
TPWRT
TOST
INTERNAL RESET
15.10 Interrupts
The PIC16F87/88 has up to 12 sources of interrupt.
The Interrupt Control register (INTCON) records indi-
vidual interrupt requests in flag bits. It also has
individual and global interrupt enable bits.
Note:
Individual interrupt flag bits are set,
regardless of the status of their
corresponding mask bit or the GIE bit.
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 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
Register, PIE1, and the peripheral interrupt enable bit
is 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 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 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.
DS30487B-page 138
Preliminary
 2003 Microchip Technology Inc.