Datasheet

PIC16F785/HV785

15.4 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 (e.g., W and STATUS

registers). This must be implemented in software.

Since the last 16 bytes of all banks are common in the

PIC16F785/HV785 (see Figure 2-2), temporary hold-

ing registers W_TEMP and STATUS_TEMP should be

placed in here. These 16 locations do not require

banking, therefore, making it easier to save and restore

context. The same code shown in Example 15-1 can

be used to:

• Store the W register

• Store the STATUS register

• Execute the ISR code

• Restore the Status (and Bank Select Bit register)

• Restore the W register

EXAMPLE 15-1: SAVING STATUS AND W REGISTERS IN RAM

Note: The PIC16F785/HV785 normally does not

require saving the PCLATH. However, if

computed GOTO’s are used in the ISR and

the main code, the PCLATH must be

saved and restored in the ISR.

MOVWF W_TEMP ;Copy W to TEMP register

SWAPF STATUS,W ;Swap status to be saved into W (swap does not affect status)

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