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44780 LCD queries

Discussion in 'Electronic Basics' started by ankur, Jul 2, 2005.

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  1. ankur

    ankur Guest

    Hi everyone,
    I am trying to use CCM1620CSL(a 44780-based LCD module) and that is
    the first LCD i am trying my hands on.
    I have interfaced the LCD to a PIC and till now, whatever program I
    run, the result is 16 black boxes on the 2nd line of LCD (it's a 16x2
    LCD). Can anyone suggest why is it happening? Isn't the LCD
    auto-initialized in the 8-bit, 1-line mode when no initialization
    routine is found ?

    I've few more questions:
    1) Can initialization be done only at the time of applying power to
    the LCD? Suppose I wish to change the entry mode in the middle of my
    program, how is it done?

    2) Ideally, what do you expect to see on the LCD screen if ONLY power
    is applied(i.e only Vdd,Vss & Vo are connected and rest of the pins are
    left open)

    Any help is welcome.
  2. Rich Webb

    Rich Webb Guest

    The initialization requirements for the 44780-style modules are strict.
    What you describe is characteristic of what happens without proper

    You're correct in that the module wakes up in 8-bit mode. However, even
    in 8-bit mode there are a few time-critical steps that need to occur to
    wake it up properly.

    A good reference is Note that
    this is for a particular manufacturer and, while the values will work
    with most 44780-compatible modules, there may be some with slightly
    different timing requirements with "clones." Consult the specific data
    sheet, if available.
    Initialization is just that. However, there are commands to clear, to
    change the operating mode, and to manipulate the display.

    Datasheets are your friends.
    One black bar. IIRC, the black bar is on line ONE and not line TWO. Any
    chance that you have the display (and interface pin numbering) reversed?
  3. ankur

    ankur Guest

    Hello Webb,
    Thank you for the elaborate suggestions. The data sheet I currently
    have, is least informative and I couldn't find any other datasheet of
    the same manufacturer on the web.

    I will work more on getting the initialization right. Can you tellme
    what is observed on the screen when it gets initialized
    successfully?(incase it is not different for different modules)

    And the black bar(16 consequtive boxes) are in the lower line(line
    TWO, i guess). And I don't think that the display might be reversed
    internally.Still, I'll find it out once i get through something.

    Thanks & Regards
  4. Rich Webb

    Rich Webb Guest

    Initialization is just to a blank screen with or without a cursor (a
    determined by the initialization).

    One thing you'll need to decide on is whether you write to the display
    with a fixed delay after each character (and a longer display after each
    "clear screen") or whether you read back the "busy bit" from the display
  5. Guest

    This page tells you how to initlize the 44780.
    Check out the links given on this page as well. My first success was a
    result of reading this page. I would forget the data-sheets, except
    for pin hookups, and timing requirements. Those things still confuse
    me sometimes.
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