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Help with electronics terms

Discussion in 'Electronic Basics' started by [email protected], Jun 19, 2007.

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  1. Guest

    I'm having a bit of difficulty understanding the following terms:

    A "pull up resistor".

    [But then I have a bit of a problem when folk say they have "added a
    load" to a circuit, with a resistor, when I would have said (in my
    logic) that a restriction had been added.
    But then like the optimist/pessimist dichotomy, it depends whether you
    are thinking of the resistor added across a short circuit, or an open
    circuit.]

    And "bit-banged serial" which I assume refers to a serial port on a
    Pic(axe) or similar processor.

    Thanks for any clarification, jack
     
  2. Guest

    Jack,

    I wouldn't try to limit yourself with the way people label
    technologies. If those labels (words) meant something, you wouldn't
    be looking for a solution for your own project.

    They can't do anything more with what they've been provided, so if you
    need to create something, don't depend on the limiting boundaries set
    forth by those who have accomplished done one thing or another.

    Over the next 20 years, resistors of every make will go completely
    extinct, including those previously designed to work with positronic
    PCs. What are you trying to build?
     
  3. Guest

    G'day, Peerdom.
    I'm mainly trying to learn. I was once accused of reinventing the
    wheel -- no, come to think of it, I've been told that several times.
    Many years ago I started making a pedal radio out of a car generator.
    Still have the bits. One day I may get it chrome plated and mount it
    on a jarrah plinth :)
    At around the same time, I did a course in programming an old CP/M
    computer with Pascal to do a simple accounting job. I was told not to
    be silly and to buy an accounting package off the shelf. I thought it
    was a much more practical effort than my overpaid seniors' effort in
    writing a similar program in FORTRAN on an old IBM mainframe using
    punch cards!
    The only bottom line to all of this wasted effort was that the big
    boss had some warped idea that anything that came out of a dot matrix
    printer was gospel. Oh, well!.

    I'm again reinventing the wheel, but hopefully learning a lot along
    the way (again).
    I want to program picaxe microcontrollers to do all sorts of neat
    things, and especially datalogging of various measurements and perhaps
    a keyless front door lock, and maybe a controller for an electric
    wheelchair.
    For the moment, I will stick with electrons and the various methods of
    impeding and encouraging their flow, but thanks for your advice, jack
     
  4. Eeyore

    Eeyore Guest

    A serial port handles one bit of data at a time by definition being only 'one
    bit wide'.

    The banging refers to handling that port, or making any general purpose I/O
    behave like a serial port, typically in low-level software (although it need
    not be) written yourself rather than letting relevent hardware ( a UART for
    example which may be on-chip) handle it for example.
    http://en.wikipedia.org/wiki/Uart

    Graham
     
  5. Bob Masta

    Bob Masta Guest

    This is needed on the output of an "open collector" (or "open drain",
    etc) type logic gate. Consider the output stage to be a simple switch
    with one side connected to ground and the other side connected to
    the output pin. The pull-up goes between the output pin and the
    power rail, so that the pin will go high when the switch is open.
    When the switch is closed, the pin is effectively shorted to ground
    so the output voltage is zero (and current flows through the pull-up).
    This means that the serial port operation is done by careful
    programming of the processor (to get the timig right, etc), as
    opposed to having a separate chip or circuit within the processor
    that is dedicated to take care of all the serial port stuff.
    The dedicated port frees up the processor, allowing
    it to do something else than babysit the port, so it's handy
    to have... but of course costs more in dollars and watts.

    Best regards,


    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
     
  6. When you add a resistor to a circuit, there are generally
    two possibilities as to how it is related to the signal
    path. The resistor can be added in series with the path, or
    in parallel to it (making an additional branch). Pull up
    resistors produce a parallel branch of a signal path to a
    positive supply, to provide a tendency for the signal
    voltage to head toward the positive supply, when all other
    influences (like an open collector transistor that pulls the
    signal line to ground, when the transistor turns on) turn
    off. It provides a default, no drive situation, voltage.
    Serial communications involve timing bit states so that they
    follow one another at the baud rate. Programming a port
    line to produce a serial output is pretty simple, with only
    a per character permission (handshaking) scheme that
    controls it. But receiving a serial stream involves syncing
    to the bit timing to the leading edge of the start bit of
    each character (in the case of asynchronous serial), and
    this is usually done with a resolution of 1/16th of the bit
    time. Writing code that does this process is called bit
    banging. The alternative is to use hardware that performs
    all these tasks, automatically, leaving your processor free
    to do other things, with just an occasional character move
    into or out of the hardware.
     
  7. Rich Grise

    Rich Grise Guest

    Eeyore got this one pretty good.
    Think of it as adding a conductance in parallel with whatever the output
    is. Conductance, being the reciprocal of resistance, means there's "more
    load" with _less_ resistance across the output terminals.

    Typically, "more load" means more current output.
    Like Eeyore said, it's just emulating a UART in software/firmware.

    Hope This Helps!
    Rich
     
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