Datasheet

© 2007 Microchip Technology Inc. DS41206B-page 73
PIC16F716
9.10.1 INT INTERRUPT
External interrupt on RB0/INT pin is edge triggered,
either rising if bit INTEDG of the OPTION register is set,
or falling if the INTEDG bit is clear. When a valid edge
appears on the RB0/INT pin, flag bit INTF of the
INTCON register is set. This interrupt can be disabled
by clearing enable bit INTE of the INTCON register.
Flag bit INTF must be cleared in software in the Inter-
rupt Service Routine 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 interrupt enable bit GIE decides
whether or not the processor branches to the interrupt
vector following wake-up. See Section 9.13
“Power-down Mode (Sleep)” for details on Sleep
mode.
9.10.2 TMR0 INTERRUPT
An overflow (FFh → 00h) in the TMR0 register will set
flag bit T0IF of the INTCON register. The interrupt can
be enabled/disabled by setting/clearing enable bit
T0IE of the INTCON register. (Section 4.0 “Timer0
Module”).
9.10.3 PORTB INTCON CHANGE
An input change on PORTB<7:4> sets flag bit RBIF of
the INTCON register. The interrupt can be
enabled/disabled by setting/clearing enable bit RBIE of
the INTCON register. (Section 3.2 “PORTB and the
TRISB Register”).
9.11 Context Saving During Interrupts
During an interrupt, only the return PC value is saved
on the stack. Typically, users may wish to save key
registers during an interrupt, (i.e., W register and
STATUS register). This will have to be implemented in
firmware.
Example 9-1 stores and restores the W, STATUS,
PCLATH and FSR registers. Context storage registers,
W_TEMP, STATUS_TEMP, PCLATH_TEMP and
FSR_TEMP, must be defined in Common RAM which
are those addresses between 70h-7Fh in Bank 0 and
between F0h-FFh in Bank 1.
The example:
a) Stores the W register.
b) Stores the STATUS register in Bank 0.
c) Stores the PCLATH register.
d) Stores the FSR register.
e) Executes the Interrupt Service Routine code
(User-generated).
f) Restores all saved registers in reverse order
from which they were stored.
EXAMPLE 9-1: SAVING STATUS, W, AND PCLATH REGISTERS IN RAM
MOVWF W_TEMP ;Copy W to TEMP register, could be bank one or zero
SWAPF STATUS,W ;Swap status to be saved into W
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
BCF STATUS, IRP ;Return to Bank 0
MOVF FSR, W ;Copy FSR to W
MOVWF FSR_TEMP ;Copy FSR from W to FSR_TEMP
:
:(ISR)
:
MOVF FSR_TEMP,W ;Restore FSR
MOVWF FSR ;Move W into FSR
MOVF PCLATH_TEMP, W ;Restore PCLATH
MOVWF PCLATH ;Move W into PCLATH
SWAPF STATUS_TEMP,W ;Swap STATUS_TEMP register into W
MOVWF STATUS ;Move W into STATUS register
SWAPF W_TEMP,F ;Swap W_TEMP
SWAPF W_TEMP,W ;Swap W_TEMP into W
RETFIE ;Return from interrupt and enable GIE