Datasheet

© 2007 Microchip Technology Inc. DS39597C-page 69
PIC16F72
11.11.1 INT INTERRUPT
External interrupt on the RB0/INT pin is edge triggered,
either rising, if bit INTEDG (OPTION<6>) is set, or fall-
ing, if the INTEDG bit is clear. When a valid edge
appears on the RB0/INT pin, flag bit INTF
(INTCON<1>) is set. This interrupt can be disabled by
clearing enable bit INTE (INTCON<4>). Flag bit INTF
must be cleared in software in the Interrupt Service
Routine before re-enabling this interrupt. The INT inter-
rupt can wake-up the processor from SLEEP, if bit INTE
was set prior to going into SLEEP. The status of global
interrupt enable bit GIE decides whether or not the
processor branches to the interrupt vector following
wake-up. See Section 11.14 for details on SLEEP
mode.
11.11.2 TMR0 INTERRUPT
An overflow (FFh → 00h) in the TMR0 register will set
flag bit TMR0IF (INTCON<2>). The interrupt can be
enabled/disabled by setting/clearing enable bit
TMR0IE (INTCON<5>) (see Section 4.0).
11.11.3 PORTB INTCON 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<4>) (see
Section 3.2).
11.12 Context Saving During Interrupts
During an interrupt, only the return PC value is saved
on the stack. Typically, users may wish to save key reg-
isters during an interrupt (i.e., W, STATUS registers).
This will have to be implemented in software, as shown
in Example 11-1.
For the PIC16F72 device, the register W_TEMP must
be defined in both banks 0 and 1 and must be defined
at the same offset from the bank base address (i.e., if
W_TEMP is defined at 20h in bank 0, it must also be
defined at A0h in bank 1). The register STATUS_TEMP
is only defined in bank 0.
EXAMPLE 11-1: SAVING STATUS, W AND PCLATH REGISTERS IN RAM
MOVWF W_TEMP ;Copy W to TEMP register
SWAPF STATUS,W ;Swap status to be saved into W
CLRF STATUS ;bank 0, regardless of current bank, Clears IRP,RP1,RP0
MOVWF STATUS_TEMP ;Save status to bank zero STATUS_TEMP register
:
:(ISR) ;Insert user code here
:
SWAPF STATUS_TEMP,W ;Swap STATUS_TEMP register into W
;(sets bank to original state)
MOVWF STATUS ;Move W into STATUS register
SWAPF W_TEMP,F ;Swap W_TEMP
SWAPF W_TEMP,W ;Swap W_TEMP into W