I can't even make an LED flash!


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  1. #1
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    Default I can't even make an LED flash!

    I'm playing with a 16F628 and for some reason I'm having significant trouble, I'm running a 4MHz crystal with 15pF caps - am running crystal rather than INTRC as I'm wanting reliable serial comms - but in the interum I can't even flash an LED - can anyone please tell me where I'm going wrong? I know it'll be something stupid but stuffed if I can figure it!

    Thanks

    @ DEVICE PIC16F628, XT_OSC, MCLR_OFF, PROTECT_OFF, BOD_ON, CPD_OFF, WDT_ON

    DEFINE OSC 4

    TRISA = %00000011
    TRISB = %10000000

    T1CON = %00000011
    VRCON = 0 ' A/D Voltage reference disabled
    CMCON = 7 'Disable comparitor
    OPTION_REG = %01010111

    PortA = 0
    PortB = 0

    start:

    portb.2 = 1
    pause 100
    portb.2 = 0
    pause 100
    goto start

  2. #2
    skimask's Avatar
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    You've got 16F628 defined. Would you by chance actually mean 16F628A?

  3. #3
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    Nup, it's just a plain old 16f628, i thought i'd blown up the chip so I tried another and no luck either - the only thing diff that I don't normally do is use a crystal - I have a long time ago but not recently

    Cheers

  4. #4
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    Quote Originally Posted by George View Post
    Nup, it's just a plain old 16f628, i thought i'd blown up the chip so I tried another and no luck either - the only thing diff that I don't normally do is use a crystal - I have a long time ago but not recently

    Cheers
    Another (probably bad) idea, I know your MCLR is defined as off, have you tried a pullup on it anyways?
    Voltage on Vdd?
    Have you let it run for more than about 10 seconds? If the LEDs are flashing at about 10 second intervals, somehow it might be getting on the internal 37khz clock instead of your 4mhz clock.
    Last edited by skimask; - 2nd April 2007 at 04:26.

  5. #5
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    You've got a great chip to play with as a starter... that's because you can run on INTERNAL OSCILLATOR and INTERNAL MCLR... that eliminates two sources of trouble for a newbie... all you have to do then is worry about putting 5v on the proper pin on the chip, and stuffing a correct program into it. Excuse me for mentioning it, and don't be offended, but you are connecting the LED the correct way around too?

  6. #6
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    Quote Originally Posted by George View Post
    I'm playing with a 16F628 and for some reason I'm having significant trouble, I'm running a 4MHz crystal with 15pF caps - am running crystal rather than INTRC as I'm wanting reliable serial comms - but in the interum I can't even flash an LED - can anyone please tell me where I'm going wrong? I know it'll be something stupid but stuffed if I can figure it!

    Thanks

    @ DEVICE PIC16F628, XT_OSC, MCLR_OFF, PROTECT_OFF, BOD_ON, CPD_OFF, WDT_ON

    DEFINE OSC 4

    TRISA = %00000011
    TRISB = %10000000

    T1CON = %00000011
    VRCON = 0 ' A/D Voltage reference disabled
    CMCON = 7 'Disable comparitor
    OPTION_REG = %01010111

    PortA = 0
    PortB = 0

    start:

    portb.2 = 1
    pause 100
    portb.2 = 0
    pause 100
    goto start
    Data sheet says to add @ DEVICE PIC16F628, PWRT_ON whenever BOD is enabled
    Also: I do not believe this chip has A/D converters so VRCON is likely not valid but I am really unsure about that.
    Last edited by Archangel; - 2nd April 2007 at 07:36.
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  7. #7
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    How about the prototyping board itself? We've had some discussion here lately about how badly those things will treat you over time, connections not working, intermittent connections, etc. I've started replacing all of mine (got tired of messing with bad connections).
    Have you tried putting the chip at the other end of the board or anything like that?

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    Quote Originally Posted by skimask View Post
    How about the prototyping board itself? We've had some discussion here lately about how badly those things will treat you over time, connections not working, intermittent connections, etc. I've started replacing all of mine (got tired of messing with bad connections).
    Have you tried putting the chip at the other end of the board or anything like that?
    Very good point! I just bought 4 replacements last month.
    If you do not believe in MAGIC, Consider how currency has value simply by printing it, and is then traded for real assets.
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    Gold is the money of kings, silver is the money of gentlemen, barter is the money of peasants - but debt is the money of slaves
    .
    There simply is no "Happy Spam" If you do it you will disappear from this forum.

  9. #9
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    Thanks for your input so far - but still nothing! The LEDs r the right way around, all the pins metered up ok - I might try the chip on INTRC to see what happens - will let you know how i get on, cheers

  10. #10
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    Got it figured! For some reason the thing won't run at under 4.2V I've been trying to run it at 3.0V - I might revert to the 628A as it's better at lower power - on saying that the datasheet for the 628 does say it will run at 3.0V Thanks for your time everyone, I should have bumped the voltage to 5 much earlier. Good suggestion too skimask about the prototype boards I've had trouble with mine in the past but for some reason i still trust them - figure that one out!

  11. #11
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    Code:
    @ DEVICE  PIC16F628, XT_OSC, MCLR_OFF, PROTECT_OFF, BOD_ON, CPD_OFF, WDT_ON
    
    DEFINE OSC 4
    
    TRISA = 000011
    TRISB = 000000
    
    T1CON = 000011
    VRCON = 0                           ' A/D Voltage reference disabled
    CMCON = 7                            'Disable comparitor
    OPTION_REG = 010111
    
    PortA = 0
    PortB = 0
    
    start:
    
        portb.2 = 1
        pause 100
        portb.2 = 0
        pause 100
        goto start
    Glad you got it working, might be BOD on causing it.
    Last edited by Archangel; - 2nd May 2012 at 00:40. Reason: remove html
    If you do not believe in MAGIC, Consider how currency has value simply by printing it, and is then traded for real assets.
    .
    Gold is the money of kings, silver is the money of gentlemen, barter is the money of peasants - but debt is the money of slaves
    .
    There simply is no "Happy Spam" If you do it you will disappear from this forum.

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