divide a 10 Mhz signal by 1000 ...


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  1. #1
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    Default divide a 10 Mhz signal by 1000 ...

    I must divide a signal (10 Mhz) to 10 Khz (OCXO asservissement with a GPS)
    I have an example in language "C" and I understand quite nothing !!! it use a 12F675 (clock is the 10 mhz signal)
    and I would like to understand why I see all those "counts" for one division

    I Hope somebody can help me, I think that I have to write in ASM language, not in Basic
    ASM is not easy for me ...
    so if somebody knows how to divide a 10 Mhz signal to get a 10 Khz output signal
    I would appreciate
    thanks
    Francois F1CHF
    here is the "code" see attached file (sorry I didn't know how to use the "code" function !)
    Attached Files Attached Files

  2. #2
    Join Date
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    Default Re: divide a 10 Mhz signal by 1000 ...

    Just cascade 3 times 4017. It cheapest and reliable way to do it.
    https://www.ti.com/lit/ds/schs027c/s...oogle.com%252F

  3. #3
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    Default Re: divide a 10 Mhz signal by 1000 ...

    I would like to understand why I see all those "counts" for one division
    its not one division its three with a 90 deg phase shift on one of them.

    one div would be like this

    Code:
    ;In simple terms  toggle a pin on every 125th cycle
    ;start:;set gpio pin high
    ;delay 124 cycles
    ;set gpio pin low
    ;delay 122 cycles
    ;goto start
    
    
    CNT VAR BYTE BANK0
    TRISIO=110
    ASM
    START
      BSF GPIO , 0  
      MOVLW 40      ;2
      MOVWF _CNT    ;1
    DL1             ;119 DELAY = 2+3(CNT-1)
      DECFSZ _CNT    
      GOTO DL1      
      NOP           ;1
      NOP           ;1
      BCF GPIO , 0  
      MOVLW 40      ;2
      MOVWF _CNT    ;1
    DL2
      DECFSZ _CNT    ;119 DELAY = 2+3(CNT-1)
      GOTO DL2      
      GOTO START    ;2
    ENDASM
    Last edited by richard; - 3rd February 2021 at 01:29.
    This is more entertaining than Free to Air TV

  4. #4
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    Default Re: divide a 10 Mhz signal by 1000 ...

    thanks for your reply, i know ths solution with divider like 74xx390 etc ... CD4017 at 10 mhz ... not sure ...
    objective : have a small unit to do the job !
    thanks
    francois

  5. #5
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    Default Re: divide a 10 Mhz signal by 1000 ...

    thanks Richard I don't see my first reply
    so I was saying
    "I am not spleeping just trying to undersatnd your asm example ..."
    hold the line !
    regards

  6. #6
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    Default Re: divide a 10 Mhz signal by 1000 ...

    i tested my code while i had the sim running, seems i cant count well

    this is better
    Code:
     #CONFIGcfg = _HS_OSC                 ; HS oscillator: High speed crystal/resonator on GP4/OSC2/CLKOUT and GP5/OSC1/CLKIN
    cfg&= _WDT_ON                 ; WDT enabled
    cfg&= _PWRTE_OFF              ; PWRT disabled
    cfg&= _MCLRE_ON               ; GP3/MCLR pin function is MCLR
    cfg&= _BODEN_ON               ; BOD enabled
    cfg&= _CP_OFF                 ; Program Memory code protection is disabled
    cfg&= _CPD_OFF                ; Data memory code protection is disabled
      __CONFIG cfg
    
    
    #ENDCONFIG
     ;pic12f675
    ;In simple terms  toggle a pin   every 125 cycles
    ;start:;set gpio pin high
    ;delay 125 cycles
    ;set gpio pin low
    ;delay 123 cycles
    ;goto start
    
    
    
    
    CNT VAR BYTE BANK0
    TRISIO=%11111110
    ASM
    START
      BSF GPIO , 0  
      MOVLW 41      ;2
      MOVWF _CNT    ;1
    DL1             ;122 DELAY = 2+3(CNT-1)
      DECFSZ _CNT,f    
      GOTO DL1
      BCF GPIO , 0  
      MOVLW 40      ;2
      MOVWF _CNT    ;1
    DL2
      DECFSZ _CNT,f    ;119 DELAY = 2+3(CNT-1)
      GOTO DL2    
      NOP           ;1  
      GOTO START    ;2
    ENDASM
    This is more entertaining than Free to Air TV

  7. #7
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    Default Re: divide a 10 Mhz signal by 1000 ...

    I got a very nice answer on that subject
    here
    Hello François

    Have an eye Here: http://www.leapsecond.com/pic/picdiv.htm

    Alain

  8. #8
    Join Date
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    Default Re: divide a 10 Mhz signal by 1000 ...

    Great idea. They use external signal as PIC clock and then execute a timed delay to toggle output. So the output has the precision of the input clock signal! Brilliant!

    Ioannis

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