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Quick Microcontroller question

Discussion in 'Misc Electronics' started by Colin, Aug 26, 2005.

  1. Colin

    Colin Guest

    With an atmel microcontroller when you write 1 to a pin does the pin
    actually read +5, or is that only when you have an internal pullup on that
  2. It reads +5 when high.
    But be aware that most atmels can sink more current than they can
  3. Rich Webb

    Rich Webb Guest

    It will be a "logic 1" but the guaranteed minimum voltage is 4.2 V.
    Check the datasheets; there is some variation among the AVR family in
    this parameter. Even with pull-ups, the actual value may be less than
    5.00 V if you're sourcing current.
  4. On the 8051 equivalents (89C52, etc.) one port is open collector, so
    requires an external pull-up, if I recall correctly.

    Read The Fascinating Manual for the particular microcontroller you are
    using to be sure....

    Peter Bennett, VE7CEI
    peterbb4 (at)
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