PIC16F818/819
FIGURE 12-6:
SLOW RISE TIME (MCLR TIED TO VDD THROUGH RC NETWORK)
5V
1V
0V
VDD
MCLR
Internal POR
TPWRT
PWRT Time-out
TOST
OST Time-out
Internal Reset
The RB0/INT pin interrupt, the RB port change interrupt
and the TMR0 overflow interrupt flags are contained in
the INTCON register.
12.10 Interrupts
The PIC16F818/819 has up to nine sources of inter-
rupt. The Interrupt Control register (INTCON) records
individual interrupt requests in flag bits. It also has
individual and global interrupt enable bits.
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.
Note:
Individual interrupt flag bits are set
regardless of the status of their
corresponding mask bit or the GIE bit.
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.
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
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.
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.
The “return from interrupt” instruction, RETFIE, exits
the interrupt routine, as well as sets the GIE bit, which
re-enables interrupts.
FIGURE 12-7:
INTERRUPT LOGIC
Wake-up (if in Sleep mode)
Interrupt to CPU
EEIF
EEIE
TMR0IF
TMR0IE
INTF
INTE
ADIF
ADIE
SSPIF
SSPIE
RBIF
RBIE
CCP1IF
CCP1IE
PEIE
GIE
TMR1IF
TMR1IE
TMR2IF
TMR2IE
DS39598E-page 96
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
