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SECTION III-5: The COMF Instruction in the PIC micro-controller
The "COMF fileReg, d" instruction complements (inverts) the contents of fileReg and places the result in WREG of fileReg. The is an example of what is called Read - Modify - Write.
In the following program, we put 55H into WREG and then send it out to SFR location of port B. Then the content of Port B is complemented, which becomes AA in hex. The 01010101 (55H) is inverted and becomes 10101010 (AAH).
| MOVLW 55H | ;WREG = 55H |
|---|---|
| MOVWF PORTB | ;move WREG to Port B SFR (PB = 55H |
| COMF PORTB, F | ;complement Port B (PB = AAH) |
| Simple Program to Toggle the SFR of PORT B continuously forever. | |
|---|---|
| MOVLW 55H | ;WREG = 55H |
| MOVWF PORTB | ;move WREG to Port B SRF (PB = 55H) |
| B1 COMF PORTB, F | ;complement Port B and place it in Port B |
| GOTO B1 | ;repeat forever |