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What does it mean trisate?

Discussion in 'Electronic Basics' started by Guest, Aug 14, 2003.

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  1. Guest

    Guest Guest

    When reading the datasheet of the picmicro microchip there are
    some terms I don't understand. What is tristate. Also, what is
    brown-out-detect?
    Tia
     
  2. A pin can be configured to output a high signal (pull towards Vdd), output a
    low signal (pull towards Vss), or it could be configured as an input (let
    the pin float in high impedance mode). A tristated pin means that it is
    configured as an input. Once it's understood that tristate and input are
    synonymous, the TRISA, TRISB, etc. register names and how the bits work seem
    quite logical.

    The brown-out-detect module measures the voltage of Vdd and when it drops
    too low (somewhere around 3V I think for PIC12F and PIC16F series), it will
    place the chip in reset. In other words, when the power supply starts
    sagging, it will detect the condition, stop executing code, tristate all the
    pins, and reset the program counter. When the voltage climbs back above a
    certain threshold, the PIC restarts executing code (but from the beginning
    since the program counter was cleared). The brown-out-detect module can be
    useful if you are switching power MOSFETs or something which would explode
    if you gave it a prolonged gate drive of only 3V or less.

    Howard Henry Schlunder
     
  3. grahamk

    grahamk Guest

     
  4. Guest

    Guest Guest

    thanks to all
     
  5. GGPP

    GGPP Guest

    Tristate means that the output can have 3 dif. states : high (V+), low(Gnd)
    and high-impedance.
    I do not know what brown-out-detect is.
    Gerard.
     
  6. Jim Large

    Jim Large Guest

    Not always. Some tristate-able pins are just outputs.
    They can drive a bus high, drive it low, or not drive
    it at all; but they can't sense the bus.

    Maybe you don't see so many of these anymore now that
    everything's microcontrollers and programmable logic,
    but it was pretty common back in the days of MSI logic.

    -- JmL
     
  7. brown out detect detects a drop in voltage between the positive supply and
    ground, and usually resets the chip or something like that..

    Tristate outputs are used in computer systems built from discrete logic for
    busses. You activate the chip using address lines, and all other chips on
    the bus that are not selected present high impedance (ie, the 'third' state)
    instead of a logic 0 or 1. That way, multiple devices can coexist on the bus
    without interfering with one another.

    In PIC land, if you configure a pin to be 'tristate' (using the TRISTA
    register), its an input rather than an output, and the output drivers are
    disconnected from the pin. This is a bit different from the original
    meaning...

    Regards,
    Bob Monsen
     
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