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PIC16F882-I Datasheet(PDF) 225 Page - Microchip Technology |
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PIC16F882-I Datasheet(HTML) 225 Page - Microchip Technology |
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225 / 328 page  © 2009 Microchip Technology Inc. DS41291F-page 223 PIC16F882/883/884/886/887 14.4 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 upper 16 bytes of all GPR banks are com- mon in the PIC16F882/883/884/886/887 (see Figures 2-2 and 2-3), temporary holding registers, W_TEMP and STATUS_TEMP, should be placed in here. These 16 locations do not require banking and therefore, make it easier to context save and restore. The same code shown in Example 14-1 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 14-1: SAVING STATUS AND W REGISTERS IN RAM Note: The PIC16F882/883/884/886/887 nor- mally 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 ;Swaps are used because they do not affect the status bits 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 |
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