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PIC Microcontoller IO Method

PIC Tachometer

By Tony Nixon [sales at bubblesoftonline.com]

Here is a quick tacho program I just whipped up.

The IRQ is based on a 100uS TMR0 overflow. It is responsible for points status, rpm counting, and display updates The main loop calculates the new display data based on the 100uS count value.

Enter your cylinders in the space shown.

You will have to write you own display multiplex code in the IRQ routine. Only digits A, B and C are used and digit D = '0' always.

         include "P16f873.inc"

         CBLOCK 0x20

nratorH
nratorM
nratorL
denomH
denomM
denomL
remainH
remainM
remainL
shiftH
shiftM
shiftL
numahi
numalo
rsltal
rsltah
rsltbh
rsltbl
LoopCt
temp
debounce
flag1
dispA
dispB
dispC
holdA
holdB
holdC
loopsH
loopsM
loopsL
DispCnt
W_hold
S_hold
         ENDC

; Xtal = 8MHz

p_stat  equ 0h  ; points STATUS flag
u_range equ 1h  ; RPM under range
do_div  equ 2h  ; do division routine
n_disp  equ 3h  ; new display data available

Points equ 0h   ; portA,0

Cylinders = 1   ; set engine cylinders

;
; CALCULATIONS BASED ON
; RPM = 927C0 / 100uS LOOPS
;

RPMconst = 927C0h / Cylinders

rpm_H = Upper(RPMconst)
rpm_M = High(RPMconst & 0xFFFF)
rpm_L = RPMconst & 0xFF

          org 0h

        goto start

        org 4h

IRQvec  movwf W_hold
        swapf STATUS,W
        movwf S_hold
        bcf INTCON,T0IF
        movlw 0xA0
        movwf TMR0

        bsf flag1,do_div        ; flag do division routine
        movf debounce   ; test points only if debounce = 0
        btfsc STATUS,Z
        goto ChkPts

        decf debounce
        goto Inc_Cnt    ; increment RPM counters

ChkPts  btfsc PORTA,Points      ; test points
        goto P_Shut

        btfss flag1,p_stat
        goto Inc_Cnt    ; already flagged as open

        bcf flag1,p_stat
        movlw 8h
        movwf debounce

        movf loopsH,W   ; prepare for calculations
        movwf denomH
        movf loopsM,W
        movwf denomM
        movf loopsL,W
        movwf denomL
        clrf loopsH
        clrf loopsM
        clrf loopsL
        bsf flag1,do_div        ; flag do division routine
        bcf flag1,u_range 
        goto Exirq

P_Shut  btfsc flag1,p_stat
        goto Inc_Cnt    ; already flagged as shut

        bsf flag1,p_stat
        movlw 8h
        movwf debounce

Inc_Cnt btfsc flag1,u_range     ; increment if under max count
        goto Exirq

        incfsz loopsL
        goto Udt_Disp
        incf loopsM
        goto Udt_Disp
        incf loopsH
        movlw 0ah               ; if = ah then RPM is < 1
        xorwf loopsH,W
        btfsc STATUS,Z
        bsf flag1,u_range
;
; ROUTINE TO UPDATE 3 x 7 SEG DISPLAYS
; DISPLAY 4 = PERMANANT 0
;
Udt_Disp        decfsz DispCnt  ; update every 100th second
        goto Exirq

        movlw d'100'
        movwf DispCnt

        btfss flag1,n_disp
        goto Olddata

        movf holdA,W
        movwf dispA
        movf holdB,W
        movwf dispB
        movf holdC,W
        movwf dispB
        bcf flag1,n_disp

        ; update display code here
Olddata

Exirq   swapf S_hold,W
        movwf STATUS
        swapf W_hold
        swapf W_hold,W
        retfie
;
; DIGIT A
; A = RB0
; B = RB1
; C = RB2
; D = RB3
; E = RB4
; F = RB5
; G = RB6
;
Nib_7seg  addwf PCL
          retlw b'00111111' ; 0
          retlw b'00000110' ; 1
          retlw b'01011011' ; 2
          retlw b'01001111' ; 3
          retlw b'01100110' ; 4
          retlw b'01101101' ; 5
          retlw b'01111101' ; 6
          retlw b'00000111' ; 7
          retlw b'01111111' ; 8
          retlw b'01101111' ; 9

; SETUP A 100uS LOOP

start   bsf STATUS,RP0
        movlw b'00000000'
        movwf OPTION_REG
        bcf STATUS,RP0

        clrf flag1
        clrf dispA
        clrf dispB
        clrf dispC
        clrf loopsH
        clrf loopsM
        clrf loopsL
        movlw d'100'
        movwf DispCnt

        bsf INTCON,T0IE ; enable TMR0 IRQ
        bsf INTCON,GIE

MnLoop  btfss flag1,do_div
        goto MnLoop

        bcf flag1,do_div
        movlw rpm_H     ; calculate RPM for display
        movwf nratorH
        movlw rpm_M
        movwf nratorM
        movlw rpm_L
        movwf nratorL

        call divizn     ; update display data
        movf nratorM,W
        movwf numahi
        movf nratorL,W
        movwf numalo
        call HexBCD     ; result is returned in rsltbl, rsltah, and rsltal

        swapf rsltah,W
        andlw 0Fh
        call Nib_7seg   ; bcd to 7 seg
        movwf holdA
        movf rsltah,W
        andlw 0Fh
        call Nib_7seg   ; bcd to 7 seg
        movwf holdB
        swapf rsltal,W
        andlw 0Fh
        call Nib_7seg   ; bcd to 7 seg
        movwf holdC
        bsf flag1,n_disp        ; flag new display data available
        goto MnLoop
        ;
        ;       ------------------------------------------
        ; SUBROUTINE - 24 BIT DIVISION
        ; numerator:        nratorH  nratorM  nratorL
        ; denominator:      denomH   denomM   denomL
        ;
        ; result:           nratorH  nratorM  nratorL
        ; remainder:        remainH  remainM  remainL
        ;
divizn    movlw .24
        movwf temp
        movf nratorH,w
        movwf shiftH
        movf nratorM,w
        movwf shiftM
        movf nratorL,w
        movwf shiftL
        clrf nratorH
        clrf nratorM
        clrf nratorL
        ;
        clrf remainH
        clrf remainM
        clrf remainL
dloop     bcf STATUS,C
        rlf shiftL
        rlf shiftM
        rlf shiftH
        rlf remainL
        rlf remainM
        rlf remainH
        movf denomH,w
        subwf remainH,w
        btfss STATUS,Z
        goto nochk
        ;
        movf denomM,w
        subwf remainM,w
        btfss STATUS,Z
        goto nochk
        ;
        movf denomL,w
        subwf remainL,w
nochk     btfss STATUS,C
        goto nogo
        ;
        movf denomL,w
        subwf remainL
        btfss STATUS,C
        decf remainM
        movf remainM,w
        xorlw 0xff
        btfsc STATUS,Z
        decf remainH
        movf denomM,w
        subwf remainM
        btfss STATUS,C
        decf remainH
        movf denomH,w
        subwf remainH
        bsf STATUS,C
nogo      rlf nratorL
        rlf nratorM
        rlf nratorH
        decfsz temp
        goto dloop
        ;
        return
        ;
        ;         ----------------------------------------------
        ; SUBROUTINE: CONVERT A NUMBER FROM HEX TO BCD
        ; 16 bit number to convert is in numahi, numalo
        ; result is returned in rsltbl, rsltah, and rsltal
        ;
HexBCD    bcf STATUS,C
        movlw .16
        movwf temp
        clrf rsltbl
        clrf rsltah
        clrf rsltal
        ;
loop16    rlf numalo
        rlf numahi
        rlf rsltal
        rlf rsltah
        rlf rsltbl
        ;
        decfsz temp
        goto adjDEC
        return
        ;
adjDEC    movlw rsltal
        movwf FSR
        call adjBCD
        movlw rsltah
        movwf FSR
        call adjBCD
        movlw rsltbl
        movwf FSR
        call adjBCD
        goto loop16
        ;
adjBCD    movlw .3
        addwf INDF,w
        movwf rsltbh        ; temp storage
        btfsc rsltbh,3
        movwf INDF
        movlw 30h
        addwf INDF,w
        movwf rsltbh
        btfsc rsltbh,7
        movwf INDF
        return

          end


Questions:

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See:


file: /Techref/microchip/tacho.htm, 9KB, , updated: 2008/10/21 14:29, local time: 2017/12/12 23:21,
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