PIC16F872_06 Datasheet, PDF (100/168 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS Flash Microcontroller with 10-Bit A/D

PIC16F872
11.10.1 INT INTERRUPT
External interrupt on the RB0/INT pin is edge triggered,
either rising if bit INTEDG (OPTION_REG<6>) is set,
or falling 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 11.13 for details on SLEEP
mode.
11.10.2 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 5.0.
11.10.3 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 4.2.
11.11 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 register and STATUS
register). This will have to be implemented in software.
Since the upper 16 bytes of each bank are common in
PIC16F872 devices, temporary holding registers,
W_TEMP, STATUS_TEMP and PCLATH_TEMP,
should be placed in here. These 16 locations don’t
require banking and therefore, make it easier for con-
text save and restore. The same code shown in
Example 11-1 can be used.
EXAMPLE 11-1: SAVING STATUS, W, AND PCLATH REGISTERS IN RAM
MOVWF
SWAPF
CLRF
MOVWF
MOVF
MOVWF
CLRF
:
:(ISR)
:
MOVF
MOVWF
SWAPF
MOVWF
SWAPF
SWAPF
W_TEMP
STATUS,W
STATUS
STATUS_TEMP
PCLATH, W
PCLATH_TEMP
PCLATH
PCLATH_TEMP, W
PCLATH
STATUS_TEMP,W
STATUS
W_TEMP,F
W_TEMP,W
;Copy W to TEMP register
;Swap status to be saved into W
;bank 0, regardless of current bank, Clears IRP,RP1,RP0
;Save status to bank zero STATUS_TEMP register
;Only required if using pages 1, 2 and/or 3
;Save PCLATH into W
;Page zero, regardless of current page
;(Insert user code here)
;Restore PCLATH
;Move W into PCLATH
;Swap STATUS_TEMP register into W
;(sets bank to original state)
;Move W into STATUS register
;Swap W_TEMP
;Swap W_TEMP into W
DS30221C-page 98
© 2006 Microchip Technology Inc.