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Reg-Serial connection

Discussion in 'Electronic Design' started by karthik, May 3, 2006.

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  1. karthik

    karthik Guest

    what is meant by serial & parralle connection in CPU.
    RS 232,USB etc
  2. Joel Kolstad

    Joel Kolstad Guest

    At the most basic level, say I want to transmit a number from 0 to 255; in
    binary this is 8 bits, e.g., 160 is 0xAA=10101010.

    In a parallel connection, I just place 10101010 on a bunch of wires; all the
    signals are being sent "in parallel."

    In a serial connection, I send 1, then 0, then 1, then 0, then 1, then 0, then
    1, and finally 0; the signals are sent as a "series" of bits.

    RS-232 and USB are serial connections, as is Firewire (IEEE-1394) and SATA.
    Traditional (Centronics) printer ports, SCSI, and IDE are parallel

    Everything else being equal, parallel connections are faster but also larger;
    a major motivation to use serial connections is the smaller number of wires or
    PCB traces needed if the serial connection can still be made "fast enough."
  3. Jon

    Jon Guest

    Serial data buses send data one bit at a time. Parallel buses send
    multiple bits simultaneously. The examples you give; RS232, USB are
    axamples of serial buses. The parallel printer port is an example of a
    parallel bus.
  4. Steve

    Steve Guest

    One question. Is it correct to describe a serial data connection as a
    "bus" ?

  5. Sure, EDA conventions notwithstanding. What do you thing the second
    and third letters in 'USB' stand for?

    Best regards,
    Spehro Pefhany
  6. Tim Auton

    Tim Auton Guest

    If it's a bus (it can connect >2 devices), like USB or RS422, then
    yes. I'm not sure if I'd call RS232 a bus.

  7. Steve

    Steve Guest

    Ah yes, that example was rather staring me in the face, here by the PC
    :). Funny, I'd always thought of a bus as a parallel sort of thing,
    but I suppose they mostly were when I was younger.

  8. Rich Grise

    Rich Grise Guest

    I think the determining factor is if there are more than two devices on
    "the bus", that can share the data line by being selected/enabled
    individually. Just point A to point B, I wouldn't call a bus.

  9. Steve

    Steve Guest

    And yet tend to refer to it as such when it's a microprocessor to
    memory parallel link, 2 "devices". Which is where I guess I got
    confused on the terminology. Hmm, but even though there are only 2
    things on that "bus" the memory can be en/dis abled so is the ability
    to switch attached devices on/off the real definition of a bus
    architecture, rather than simply n>2?

  10. Rich Grise

    Rich Grise Guest

    [somebody whose name got snipped wrote:]
    I think you're mixing metaphors here. Even if you connect a uP to only one
    memory chip, there's still an "address bus" and a "data bus", but that's
    because they're parallel, and _could_ be expanded to accomodate more
    devices; each one has its own enable. This _can_ be done with a serial
    protocol, which would give you a "serial bus", but I think they're fairly
    well-defined in the specs somewhere. Have you tried a google on "serial

    Good Luck!
  11. Steve

    Steve Guest

    Ah, I see your point, thanks!

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