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pic16c54 crystal not oscillating

Discussion in 'Electronic Design' started by Ryan Gammon, Jan 19, 2004.

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  1. Ryan Gammon

    Ryan Gammon Guest

    Hello folks, I have a Avermedia TV98 tv capture card (it's labeled as
    M1A8-A on [1]). This card has a remote control which is handled by a
    pic16c54 chip.

    I've found that after moving the card from an old PII to a new P4
    system, the remote control no longer works.

    The PIC is connected to a 4 MHz crystal. On the PII, I can probe pin
    15 and always get a 4 MHz signal. On the P4, I don't get a clock.

    The pic is connected to the Vdd and Vss of the pci card.

    Does anyone know why the 4 MHz crystal doesn't start up when the card
    is in the P4 system?



  2. Obvious thing, is to look elsewhere first.
    Check that the chip has got it's supply, that the voltage is correct, and
    that the MCLR line has gone high.
    Remember that the main power lines on PCI, can be 5v, or 3.3v, according to
    version. Technically the cards should be keyed to prevent incorrect
    insertion. I'd expect the P4, to only support 3.3v cards.

    Best Wishes
  3. Ryan Gammon

    Ryan Gammon Guest

    Turns out that my new system has three states of powered-ness: off,
    power supply is on but system is suspended until the front power
    button is pressed, and on.

    When the system is suspended, the pci bus is, for whatever reason,
    getting about 1.5 V on the 5V rail (seems a little weird to me).

    Thus, the PIC starts off at 0V supply with the system off, then gets
    1.5V when the power supply is turned on, and the full 5V when the
    front button is pressed.

    Under these conditions, the crystal doesn't start.

    To solve this, I tied the /MCLR pic pin (connected to an RC circuit)
    to the PCI reset line.

    The reset pulse from the pci bus on system startup gets the crystal up
    and running, and my remote works again.

    Thanks to those who responded!

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