; USE THE BIT MASK TO ISOLATE THE CORRECT BIT IN THE BYTE
; PART OF THE REASON FOR THIS SCHEME IS BECAUSE NORMAL TABLE LOOKUP
; REQUIRES AN ADDITIONAL STACK LEVEL
CLRC ; CLEAR CARRY (FOR THE LEFT SHIFT)
MOVLW 1 ; INITIALISE MASK = 1
BTFSC HOP3,3 ; SHIFT MASK 4X IF BIT 2 SET
MOVLW 10000B ; SHIFT MASK 4X IF BIT 2 SET
MOVWF MASK ; INITIALISE MASK = 1
BTFSS HOP2,0 ; SHIFT MASK ANOTHER 2X IF BIT 1 SET
GOTO $+3
RLF MASK,F
RLF MASK,F
BTFSC HOP1,0 ; SHIFT MASK ANOTHER 1X IF BIT 0 SET
RLF
MASK,F
; MASK HAS NOW BEEN SHIFTED 0-7 TIMES ACCORDING TO BITS 2:1:0
MOVLW 0 ; TABLE INDEX = 0
BTFSC HOP4,1
IORLW 2 ; IF BIT 3 SET ADD 2 TO THE TABLE INDEX
BTFSC HOP4,6
IORLW 4 ; IF BIT 4 SET ADD 4 TO THE TABLE INDEX
ADDWF PC,F ; ADD THE INDEX TO THE PROGRAM COUNTER
; [ MUST BE IN LOWER HALF OF PAGE ]
TABLE
MOVLW 02EH ; BITS 4:3 WERE 00
GOTO TABLE_END ; END OF LOOKUP
MOVLW 074H ; BITS 4:3 WERE 01
GOTO TABLE_END ; END OF LOOKUP
MOVLW 05CH ; BITS 4:3 WERE 10
GOTO TABLE_END ; END OF LOOKUP
MOVLW 03AH ; BITS 4:3 WERE 11
TABLE_END
ANDWF MASK,F ; ISOLATE THE CORRECT BIT BY ANDING WITH MASK
MOVLW 0 ; COPY THE BIT TO BIT 7
SKPZ; ; COPY THE BIT TO BIT 7
MOVLW 10000000B ; COPY THE BIT TO BIT 7
XORWF HOP2,W ; ONLY INTERESTED IN BIT HOP2,7
XORWF HOP4,W ; ONLY INTERESTED IN BIT HOP4,7
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