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Maths Routine Problem???

natur3 t0mAt0

Hi all,

I managed to get my interrupts working, and i have figured out a way to calculate the heart rate which is:

z = 60/(0.39*R7) = 153.84/R7 = 154/R7

But when i tried this formula, the LCD only display 77 BPM and 154 BPM. It seems that the overflow counter, R7, only count 1 - 2.

This is my code:

;***************************************
;-----------INTERRUPT CONFIGURATIONS-----------
;***************************************
SETB EA          ; Enable Global Interrupts
SETB ET0         ; Enable Timer 0 Interrupt
SETB EX0         ; Enable External Interrupt 0
SETB PX0         ; External Interrupt 0 High Priority

;***************************************
;------------TIMER 0 CONFIGURATIONS------------
;***************************************
TIMER_0 EQU 65535
SETB IT0          ; External Interrupt 0 detect falling-edge
MOV TMOD,#01H   ; Set Timer 0 to Mode 1
MOV A,CKCON     ; Move CKCON to Accumualtor
CLR ACC.3       ; Set system clock to divided by 12
MOV 70H,#00H    ; Move 0 to 70H
MOV R7,#02H     ; Move 4 to R7
MOV 62H,#01H    ; Move 1 to 62H
MOV TH0,#HIGH TIMER_0 ; Set High Byte of Timer 0
MOV TL0,#LOW TIMER_0  ; Set Low Byte of Timer 0

;**********************
;-Wait Until 4th Pulse-
;**********************
WAIT:   CJNE R7,#00H,WAIT  ; Compare and jump to subroutine "WAIT" if R7 != 0
CLR TR0 ; Stop Timer 0

;******
;-Math-
;******
MATH:   MOV A,#9AH      ; Move 154 to A
        MOV B,70H
        DIV AB
        MOV R6,A

;**********************
;-External Interrupt 0-
;**********************
EX_INT0:        DJNZ 62H,COUNT  ; Decrement 62H and jump if != 0
        SETB TR0        ; Start Timer 0

COUNT:  DEC R7          ; Decrement R7
        RETI            ; Return from Interrupt

;***********************
;-Timer 0 Overflow Flag-
;***********************
T0_INT: INC 70H                 ; Overflow Counter
             MOV TH0,#HIGH TIMER_0      ; Reloads Timer 0 with High Byte
        MOV TL0,#LOW TIMER_0    ; Reloads Timer 0 with Low Byte
        RETI                    ; Return from Interrupt

Any advice would be greatly apprectiated.

Parents
  • 0 in reply to natur3 t0mAt0

    I am inputting it to the 8051 chip...

    In that case, you need to refer to (i.e. read) the datasheet of your chip.

    It will tell you which voltages on the logic input pins the chip will consider LOW and HIGH.

    If you input a signal with 0.7V p-p to a logic input pin, of course the chip will not detect any changes of that pin - because for a logic input pin, any voltage below a certain threshold is 0.

    For the frequency limitation - that is an issue with your algorithm. A '51 should easily be able to deal with input frequencies in the kHz range if programmed correctly.

Reply
  • 0 in reply to natur3 t0mAt0

    I am inputting it to the 8051 chip...

    In that case, you need to refer to (i.e. read) the datasheet of your chip.

    It will tell you which voltages on the logic input pins the chip will consider LOW and HIGH.

    If you input a signal with 0.7V p-p to a logic input pin, of course the chip will not detect any changes of that pin - because for a logic input pin, any voltage below a certain threshold is 0.

    For the frequency limitation - that is an issue with your algorithm. A '51 should easily be able to deal with input frequencies in the kHz range if programmed correctly.

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