Datasheet
1997-2013 Microchip Technology Inc. DS30234E-page 139
PIC16C6X
13.6 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.
Example 13-1 stores and restores the STATUS and W
registers. Example 13-2 stores and restores the
STATUS, W, and PCLATH registers (Devices with
paged program memory). For all PIC16C6X devices
with greater than 1K of program memory (all devices
except PIC16C61), the register, W_TEMP, must be
defined in all banks and must be defined at the same
offset from the bank base address (i.e., if W_TEMP is
defined at 0x20 in bank 0, it must also be defined at
0xA0 in bank 1, 0x120 in bank 2, and 0x1A0 in bank 3).
The examples:
a) Stores the W register
b) Stores the STATUS register in bank 0
c) Stores PCLATH
d) Executes ISR code
e) Restores PCLATH
f) Restores STATUS register (and bank select bit)
g) Restores W register
Applicable Devices
61 62 62A R62 63 R63 64 64A R64 65 65A R65 66 67
EXAMPLE 13-1: SAVING STATUS AND W REGISTERS IN RAM (PIC16C61)
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
:
:(ISR)
:
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
EXAMPLE 13-2: SAVING STATUS, W, AND PCLATH REGISTERS IN RAM
(ALL OTHER PIC16C6X DEVICES)
MOVWF W_TEMP ;Copy W to TEMP register, could be bank one or zero
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
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 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