Code:
LIST P=16F676 ; DIRECTIVE TO DEFINE PROCESSOR
;--------------------------------------------------------------------------------------------------------------------------------------
; VARIABLES USED IN BANK 0 (HEX 20-5F), ALSO ACCESSABLE FROM FROM BANK 1 (HEX A0-DF)
EEPROMCOUNT EQU 0X49 ; USED IN THE FIVE-FOLD EEPROM SAVE
EEPROMADDR EQU 0X50 ; USED IN THE FIVE-FOLD EEPROM SAVE
EEPROMDATA EQU 0X51 ; USED IN THE FIVE-FOLD EEPROM SAVE
MAJORITY EQU 0x52 ; USED IN THE EEPROM LOAD SUBROUTINE TO CALCULATE THE RESULT OF THE MAJORITY CHECK
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EEPROM_SAVE_5 BANK1 ; WRITE ONE BYTE FIVE-FOLD INTO PIC INTERNAL EEPROM
MOVLW D'5' ; PREPARE FIVE-FOLD SAVE
MOVWF EEPROMCOUNT ;
EESAVE_5_LOOP BTFSC EECON1,WR ; EACH EEPROM BYTE WRITE CAN TAKE UP TO 6 MILLISECONDS, DID WE FINISH ANY PREVIOUS WRITE ?
GOTO EESAVE_5_LOOP ; NO, NOT YET, WAIT A BIT MORE
MOVF EEPROMADDR,W ; YES, MAKE SURE THE EEPROM ADDRESS AND DATA BYTES HOLD THE RIGHT VALUE,
MOVWF EEADR ; THE STATUS OF THESE BYTES AFTER A WRITE IS UNKNOWN (AND UNDOCUMENTED)
MOVF EEPROMDATA,W ;
MOVWF EEDATA ;
BSF EECON1,WREN ; ENABLE EEPROM WRITES
; BCF INTCON,GIE ; DISABLE INTERRUPTS < ARE ALREADY DISABLED >
MOVLW H'55' ; WRITE UNLOCK CODE 1
MOVWF EECON2 ; UNLOCK WRITE
MOVLW H'AA' ; WRITE UNLOCK CODE 2
MOVWF EECON2 ; UNLOCK WRITE
BSF EECON1,WR ; ACTIVATE WRITE
BCF EECON1,WREN ; DISABLE EEPROM WRITES
; BSF INTCON,GIE ; RE-ENABLE INTERRUPTS < WILL BE ENABLED ELSEWHERE >
INCF EEPROMADDR,F ; SELECT NEXT WRITE ADDRESS
DECFSZ EEPROMCOUNT,F ; DID WE WRITE ALL FIVE BYTES ?
GOTO EESAVE_5_LOOP ; NO, GO WRITE NEXT BYTE
RETURN ; DONE
;--------------------------------------------------------------------------------------------------------------------------------------
EEPROM_READ ; THE VALUES ARE STORED IN PIC INTERNAL EEPROM. DUE TO POWER FAILURE DURING SAVES OR DUE TO
; OTHER CAUSES THE STORED VALUES MAY BECOME ERRORNOUS. TO MAKE SURE WE GET THE RIGHT VALUES
; WE STORE THEM IN FIVE-FOLD. USING A MAJORITY CHECK WE CAN CIRCUMVENT FALSE BYTES.
; WE WANT AT LEAST THREE OUT OF FIVE (MAJORITY CHECK):
; TRUTH TABLE: KARNAUGH MAP:
;
; EDCBA Y DE DE DE DE
; 0 00000 0 CBA 00 01 10 11
; 1 00001 0
; 2 00010 0 000 0 0 0 0
; 3 00011 0 001 0 0 0 1
; 4 00100 0 010 0 0 0 1
; 5 00101 0 011 0 1 1 1
; 6 00110 0 100 0 0 0 1
; 7 00111 1 101 0 1 1 1
; 8 01000 0 110 0 1 1 1
; 9 01001 0 111 1 1 1 1
; 10 01010 0
; 11 01011 1
; 12 01100 0
; 13 01101 1
; 14 01110 1
; 15 01111 1
; 16 10000 0
; 17 10001 0 BOOLEAN EQUATIONS:
; 18 10010 0
; 19 10011 1 RESULT = A AND B AND C
; 20 10100 0 OR
; 21 10101 1 (A OR B OR C) AND D AND E
; 22 10110 1 OR
; 23 10111 1 (A OR B) AND NOT(A XOR B XOR C) AND (D OR E)
; 24 11000 0
; 25 11001 1
; 26 11010 1
; 27 11011 1
; 28 11100 1
; 29 11101 1
; 30 11110 1
; 31 11111 1
BANK1 ; READ BYTE FROM PIC INTERNAL EEPROM, USE MAJORITY CHECK ONE THE FIVE-FOLD VALUE
BSF EECON1,RD ; PERFORM THE EEPROM READ OPERATION, CURRENT ADDRESS: A
BTFSC EECON1,RD ; MAKE SURE THE READ HAS FINISHED, SEEMS TO BE A PROBLEM ON SOME PIC'S
GOTO $-1 ;
COMF EEDATA,W ; W = NOT(A)
INCF EEADR,F ; SELECT NEXT READ ADDRESS: B
BSF EECON1,RD ; PERFORM THE EEPROM READ OPERATION
BTFSC EECON1,RD ;
GOTO $-1 ;
XORWF EEDATA,W ; W = NOT(A XOR B)
INCF EEADR,F ; NEXT ADDRESS: C
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
XORWF EEDATA,W ; W = NOT(A XOR B XOR C)
MOVWF MAJORITY ; R = NOT(A XOR B XOR C)
INCF EEADR,F ; NEXT ADDRESS: D
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
MOVF EEDATA,W ; W = D
INCF EEADR,F ; NEXT ADDRESS: E
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
IORWF EEDATA,W ; W = D OR E
ANDWF MAJORITY,F ; R = (D OR E) AND NOT(A XOR B XOR C)
MOVLW D'4' ;
SUBWF EEADR,F ; NEXT ADDRESS: A
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
MOVF EEDATA,W ; W = A
INCF EEADR,F ; NEXT ADDRESS: B
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
IORWF EEDATA,W ; W = A OR B
ANDWF MAJORITY,F ; R = (A OR B) AND (D OR E) AND NOT(A XOR B XOR C)
DECF EEADR,F ; NEXT ADDRESS: A
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
MOVF EEDATA,W ; W = A
INCF EEADR,F ; NEXT ADDRESS: B
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
IORWF EEDATA,W ; W = A OR B
INCF EEADR,F ; NEXT ADDRESS: C
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
IORWF EEDATA,W ; W = A OR B OR C
INCF EEADR,F ; NEXT ADDRESS: D
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
ANDWF EEDATA,W ; W = (A OR B OR C) AND D
INCF EEADR,F ; NEXT ADDRESS: E
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
ANDWF EEDATA,W ; W = (A OR B OR C) AND D AND E
IORWF MAJORITY,F ; R = ((A OR B OR C) AND D AND E) OR ((D OR E) AND NOT(A XOR B XOR C))
MOVLW D'4' ;
SUBWF EEADR,F ; NEXT ADDRESS: A
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
MOVF EEDATA,W ; W = A
INCF EEADR,F ; NEXT ADDRESS: B
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
ANDWF EEDATA,W ; W = A AND B
INCF EEADR,F ; NEXT ADDRESS: C
BSF EECON1,RD ;
BTFSC EECON1,RD ;
GOTO $-1 ;
ANDWF EEDATA,W ; W = A AND B AND C
IORWF MAJORITY,W ; W = (A AND B AND C) OR ((A OR B OR C) AND D AND E) OR ((D OR E) AND NOT(A XOR B XOR C))
RETURN ; DONE, RETURN WITH VALUE IN W REGISTER
;--------------------------------------------------------------------------------------------------------------------------------------
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