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little mistery on a hd44780 compatible LCD

Discussion in 'Electronic Design' started by blisca, Jun 1, 2007.

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  1. blisca

    blisca Guest

    Hi to all

    At power up i am often stuck with black squares on a varitronix LCD
    display, that i use just for test in place of a Powertip LCD(that i have not
    in this moment).
    No software delay looks able to fix the problem.


    touching the ENA pin(commonly pin 6),or connecting it to GND through 1 MOhm
    solves completely the problem
    Why?
    This pin is driven by the RA0 output of a PIC16f628 ,that being a CMOS
    output should not need any external pull up or pull down.
    The initialization is done following the sequence on data sheet,in 4 bit
    mode,and i write checkin the busy flag.

    Thank you!
    Diego.
     
  2. Ben Jackson

    Ben Jackson Guest

    Probably you have left RA0 in its default analog mode. All PIC pins
    that have analog capabilities come up in analog mode, just because
    you might have an arbitrary voltage connected. Even though analog mode
    is usually not what you want.

    In the case of the 16F628, it's the analog comparator. From some source
    of mine, I think you want:

    movlw b'00000111' ; comparator off
    movwf CMCON

    Other PIC chips will have other analog devices you will want to turn off
    if you're using all digital.
     
  3. blisca

    blisca Guest


    I did it exactly in this way,but thanks

    being the cable( about 3.1 inches long) the main difference with the
    original model i'm thinking to a ringing or something loike this,but sadly i
    dont have a digital scope in this moment

    thanks again
     
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