;;;;;;; RPG subroutine ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
; This subroutine decyphers RPG changes into values of DELRPG of 0, +1, or -1.
; DELRPG = +1 for CW change, 0 for no change, and -1 for CCW change.

RPG
        clrf  DELRPG            ;Clear for "no change" return value
        movf  PORTD,W           ;Copy PORTD into W
        movwf  TEMP             ; and TEMP
        xorwf  OLDPORTD,W       ;Any change?
        andlw  B'00000011'      ;If not, set Z flag
        IF_  .NZ.               ;If the two bits have changed then...
          rrcf  OLDPORTD,W      ;Form what a CCW change would produce
          IF_  .C.              ;Make new bit 1 = complement of old bit 0
            bcf  WREG,1
          ELSE_
            bsf  WREG,1
          ENDIF_
          xorwf  TEMP,W         ;Did the RPG actually change to this output?
          andlw  B'00000011'
          IF_  .Z.              ;If so, then change  DELRPG to -1 for CCW
            decf  DELRPG,F
          ELSE_                 ;Otherwise, change DELRPG to  +1 for CW
            incf  DELRPG,F
          ENDIF_
        ENDIF_
        movff  TEMP,OLDPORTD    ;Save PORTD as OLDPORTD for ten ms from now
        return


;(a) The subroutine


        rcall  RPG              ;Decypher RPG inputs into DELRPG
        movf  DELRPG,W
        addwf  RPGCNT,F         ;Increment or decrement RPGCNT from RPG
        DISPLAY  RPGCNT         ;Display RPGCNT as a binary number


;(b) Test code for mainline loop


        OLDPORTD                ;Holds previous value of RPG inputs
        TEMP                    ;Temporary local variable
        DELRPG                  ;Generated by RPG
        RPGCNT                  ;Used to display RPG changes


;(c) Variables


        movff  PORTD,OLDPORTD   ;Initialize "old" value
        clrf  RPGCNT            ;Clear counter to be displayed


;(d) Initialization


;Figure 8-3   RPG subroutine.







;;;;;;; RateRPG subroutine ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
; This subroutine decyphers RPG changes into values of DELRPG.
; DELRPG = +2 for fast CW change, +1 for slow CW change, 0 for no change,
;          -1 for slow CCW change and -2 for fast CCW change.

Threshold equ  3                ;Value to distinguish between slow and fast

RateRPG
        bcf  PORTA,RA2          ;Turn LED off
        clrf  DELRPG            ;Clear for "no change" return value
        movf  PORTD,W           ;Copy PORTD into W
        movwf  TEMP             ; and TEMP
        xorwf  OLDPORTD,W       ;Any change?
        andlw  B'00000011'      ;If not, set Z flag
        IF_  .NZ.               ;If the two bits have changed then...
          rrcf  OLDPORTD,W      ;Form what a CCW change would produce
          IF_  .C.              ;Make new bit 1 = complement of old bit 0
            bcf  WREG,1
          ELSE_
            bsf  WREG,1
          ENDIF_
          xorwf  TEMP,W         ;Did the RPG actually change to this output?
          andlw  B'00000011'
          IF_  .Z.              ;If so, then change  DELRPG to -1 for CCW
            decf  DELRPG,F
            movf  THR,F
            IF_  .NZ.
              decf  DELRPG,F    ;If fast turning, decrement again
              bsf  PORTA,RA2    ;Turn LED on
            ENDIF_
          ELSE_                 ;Otherwise, change DELRPG to  +1 for CW
            incf  DELRPG,F
            movf  THR,F
            IF_  .NZ.
              incf  DELRPG,F    ;If fast turning, increment again
              bsf  PORTA,RA2    ;Turn LED on
            ENDIF_
          ENDIF_
          MOVLF  Threshold+1,THR  ;Reinitialize THR
        ENDIF_
        movf  THR,F             ;Does THR equal zero
        IF_  .NZ.               ;If not, then decrement it
          decf  THR,F
        ENDIF_
        movff  TEMP,OLDPORTD    ;Save PORTD as OLDPORTD for ten ms from now
        return


;Figure 8-4   Rate-sensitive RateRPG subroutine with Threshold=3.