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PIC18F6585/8585/6680/8680

DS30491C-page 124

2004 Microchip Technology Inc.

9.6

INT0 Interrupt

External interrupts on the RB0/INT0, RB1/INT1, RB2/

INT2 and RB3/INT3 pins are edge-triggered: either ris-

ing 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.

The interrupt priority for INT, INT2 and INT3 is deter-

mined 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 (0FFh

→ 00h) will set flag bit TMR0IF. In

16-bit mode, an overflow in the TMR0H:TMR0L regis-

ters (0FFFFh

→ 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.

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 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.

EXAMPLE 9-1:

SAVING STATUS, WREG AND BSR REGISTERS IN RAM

MOVWF

W_TEMP

; W_TEMP is in virtual bank

MOVFF

STATUS, STATUS_TEMP

; STATUS_TEMP located anywhere

MOVFF

BSR, BSR_TEMP

; BSR located anywhere

;

; USER ISR CODE

;

MOVFF

BSR_TEMP, BSR

; Restore BSR

MOVF

W_TEMP, W

; Restore WREG

MOVFF

STATUS_TEMP, STATUS

; Restore STATUS

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