PIC16F872 Datasheet, PDF (106/160 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH Microcontroller

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 rou-
tine before re-enabling this interrupt. The INT interrupt
can wake-up the processor from SLEEP, if bit INTE was
set prior to going into SLEEP. The status of global inter-
rupt enable bit GIE decides whether or not the proces-
sor 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 T0IF (INTCON<2>). The interrupt can be
enabled/disabled by setting/clearing enable bit T0IE
(INTCON<5>) (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>)
(Section 3.2).
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
the 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. Example 11-1 can be used to
save and restore context for interrupts.
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
MOVF
PCLATH, W
;Only required if using pages 1, 2 and/or 3
MOVWF PCLATH_TEMP
;Save PCLATH into W
CLRF
PCLATH
;Page zero, regardless of current page
:
:(ISR)
:
MOVF
PCLATH_TEMP, W ;Restore PCLATH
MOVWF PCLATH
;Move W into PCLATH
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
DS30221A-page 106
Preliminary
© 1999 Microchip Technology Inc.