PIC18F1220_07 Datasheet, PDF (87/308 Pages) Microchip Technology – 18/20/28-Pin High-Performance, Enhanced Flash Microcontrollers with 10-bit A/D and nanoWatt Technology

PIC18F1220/1320
9.6 INTn Pin Interrupts
External interrupts on the RB0/INT0, RB1/INT1 and
RB2/INT2 pins are edge-triggered: either rising if the
corresponding INTEDGx bit is set in the INTCON2 reg-
ister, or falling if the INTEDGx bit is clear. When a valid
edge appears on the RBx/INTx pin, the corresponding
flag bit, INTxF, is set. This interrupt can be disabled by
clearing the corresponding enable bit, INTxE. Flag bit,
INTxF, must be cleared in software in the Interrupt
Service Routine before re-enabling the interrupt. All
external interrupts (INT0, INT1 and INT2) can wake-up
the processor from low-power modes if bit INTxE was
set prior to going into low-power modes. If the Global
Interrupt Enable bit, GIE, is set, the processor will
branch to the interrupt vector following wake-up.
Interrupt priority for INT1 and INT2 is determined by the
value contained in the interrupt priority bits, INT1IP
(INTCON3<6>) and INT2IP (INTCON3<7>). There is
no priority bit associated with INT0. It is always a high
priority interrupt source.
9.7 TMR0 Interrupt
In 8-bit mode (which is the default), an overflow
(FFh → 00h) in the TMR0 register will set flag bit,
TMR0IF. In 16-bit mode, an overflow (FFFFh → 0000h)
in the TMR0H:TMR0L registers will set flag bit,
TMR0IF. The interrupt can be enabled/disabled by
setting/clearing enable bit, TMR0IE (INTCON<5>).
Interrupt priority for Timer0 is determined by the value
contained in the interrupt priority bit, TMR0IP
(INTCON2<2>). See Section 11.0 “Timer0 Module”
for further details on the Timer0 module.
9.8 PORTB Interrupt-on-Change
An input change on PORTB<7:4> sets flag bit, RBIF
(INTCON<0>). The interrupt can be enabled/disabled
by setting/clearing enable bit, RBIE (INTCON<3>).
Interrupt priority for PORTB interrupt-on-change is
determined by the value contained in the interrupt
priority bit, RBIP (INTCON2<0>).
9.9 Context Saving During Interrupts
During interrupts, the return PC address is saved on the
stack. Additionally, the WREG, Status and BSR registers
are saved on the fast return stack. If a fast return from
interrupt is not used (see Section 5.3 “Fast Register
Stack”), the user may need to save the WREG, Status
and BSR registers on entry to the Interrupt Service
Routine. Depending on the user’s application, other
registers may also need to be saved. Example 9-1
saves and restores the WREG, Status and BSR
registers during an Interrupt Service Routine.
EXAMPLE 9-1: SAVING STATUS, WREG AND BSR REGISTERS IN RAM
MOVWF W_TEMP
MOVFF STATUS, STATUS_TEMP
MOVFF BSR, BSR_TEMP
;
; USER ISR CODE
;
MOVFF BSR_TEMP, BSR
MOVF W_TEMP, W
MOVFF STATUS_TEMP, STATUS
; W_TEMP is in virtual bank
; STATUS_TEMP located anywhere
; BSR_TMEP located anywhere
; Restore BSR
; Restore WREG
; Restore STATUS
© 2007 Microchip Technology Inc.
DS39605F-page 85