DM164120-1 Microchip Technology, DM164120-1 Datasheet - Page 34

• Manufacturer Part Number: DM164120-1
• Description: BOARD DEMO PICKIT 2 LP COUNT
• Manufacturer: Microchip Technology
• Type: MCUr

Specifications of DM164120-1

• Contents: 3 Boards (1 Populated, 2 Bare)
• Processor To Be Evaluated: PIC16F690
• Silicon Manufacturer: Microchip
• Core Architecture: PIC
• Core Sub-architecture: PIC16
• Silicon Core Number: PIC16F
• Silicon Family Name: PIC16F6xxx
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: 28-pin PIC16C, 16F, 18C, 18F
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Low Pin Count Demo Board User’s Guide
DS51556A-page 30
Restore Context
Once the peripheral is serviced, it needs to restore the context and resume the main
program. Restoring the context is a little harder than it might seem at first. The obvious
method doesn’t work because the MOVF W_Temp,w may affect the Z flag, which was
restored in the previous instruction. Instead, a pair of SWAPF instructions can restore
Wreg without affecting the flags in the Status register. SWAPF exchanges the high and
low nibbles. The first SWAPF switches the nibbles in the file register and the second one
switches them back and puts the result in Wreg.
EXAMPLE 3-9:
Finally, RETFIE transfers control back to the original program and sets the GIE bit,
re-enabling interrupts.
FIGURE 3-10:
;incorrect context restore
MOVF
MOVWF STATUS
MOVF
;good context restore
MOVF
MOVWF STATUS
SWAPF W_Temp,f
SWAPF W_Temp,w
STATUS_Temp,w
W_Temp
STATUS_Temp,w
Before
SWAPF INSTRUCTION
CONTEXT RESTORE
After
1 0 1 0
0 0 1 1
;this may change the Z bit
;in the Status register
;swap in place
;swap with Wreg destination
0 0 1 1
1 0 1 0
© 2005 Microchip Technology Inc.