PIC18F6525/6621/8525/8621
9.6
INT0 Interrupt
9.8
PORTB Interrupt-on-Change
External interrupts on the RB0/INT0/FLT0, RB1/INT1,
RB2/INT2 and RB3/INT3 pins are edge-triggered;
either rising if the corresponding INTEDGx bit is set in
the INTCON2 register, 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, INT2 and
INT3) can wake-up the processor from Sleep if bit
INTxIE was set prior to going into Sleep. If the Global
Interrupt Enable bit, GIE, is set, the processor will
branch to the interrupt vector following wake-up.
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 an interrupt, the return PC value 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 4.3 “Fast
Register Stack”), the user may need to save the
WREG, STATUS and BSR registers in software.
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.
The interrupt priority for INT1, INT2 and INT3 is
determined by the value contained in the interrupt priority
bits: INT1IP (INTCON3<6>), INT2IP (INTCON3<7>) and
INT3IP (INTCON2<1>). 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 in the
TMR0 register (FFh → 00h) will set flag bit TMR0IF. In
16-bit mode, an overflow in the TMR0H:TMR0L
registers (FFFFh → 0000h) 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.
EXAMPLE 9-1:
SAVING STATUS, WREG AND BSR REGISTERS IN RAM
MOVWF
MOVFF
MOVFF
;
W_TEMP
STATUS, STATUS_TEMP
BSR, BSR_TEMP
; W_TEMP is in virtual bank
; STATUS_TEMP located anywhere
; BSR located anywhere
; USER ISR CODE
;
MOVFF
MOVF
MOVFF
BSR_TEMP, BSR
W_TEMP, W
STATUS_TEMP, STATUS
; Restore BSR
; Restore WREG
; Restore STATUS
DS39612B-page 102
2005 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
