Problem replacing 16x1 LCD with 16x2 LCD

Discussion in 'Embedded Systems and Microcontrollers' started by JMark, Mar 4, 2014.

  1. JMark

    Thread Starter New Member

    Mar 3, 2014
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    HI, Not to hijack this thread but on similar topic I replaced a single line LCD with a 16x2 HD44780. I did not realize my error until it was all soldered in place. The device now will only display 8 characters on a line before dropping the rest of the text to the next line. Is this just a wiring problem or is this replacement not going to work? Thanks
     
    Last edited by a moderator: Mar 4, 2014
  2. MrChips

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    Oct 2, 2009
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    Sorry, that was a hijack. Now you have your own thread.
     
  3. MrChips

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    Oct 2, 2009
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    This ought to have worked with only 16-character output.
    Is this your own project, i.e. do you have access to the code?
     
  4. JMark

    Thread Starter New Member

    Mar 3, 2014
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    Yes, that did look bad. Much better, thanks. It's not my project, I replaced a non-backlit display on a vintage dedicated chess computer with this backlit one. I started from pin #1 and removed and soldered the wires one at a time. I'm powering the backlight (pin 15&16) from the bench right now until I can see if this will work.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Many of those old 16x1 text LCDs use addressing where the 16 chars are actually addressed as two lines of 8 chars.

    To use those LCDs, the software must send address codes for line 1 and line 2, and each line 8 characters.

    So if you replace it with a modern 16x2 LCD the old text will apear as 8 chars on line 1 and 8 chars on line 2.

    The only way to fix it is to find a 16x1 LCD with the same addressing scheme, OR to re-write the software to address one line of 16 chars.

    Or if you were a real genius you might have some success putting a high speed micro between the vintage machine and the new display, to capture and modify the "move to address" commands.

    Personally I would look for an old stock 16x1 LCD. You can pull them out of old FAX machines or buy one from a surplus dealer.
     
  6. JMark

    Thread Starter New Member

    Mar 3, 2014
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    OK, thanks for this information. Worse case I still have the original LCD. I had taken it apart to remove the foil and add a diffuser and LED's. It was successful but then I came across a new one that looked like it would work. Strangely sometimes it breaks the line at six, seven or eight characters. So is it likely that a modern 16x1 display would not work either? (such as this one)

    http://www.ebay.com/itm/291015059719?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
     
  7. JohnInTX

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    Jun 26, 2012
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    Good catch, Roman. Just looked at some old code that used a 16x1 and the first character is address 0x00, the 8th char starts at address 0x40. The initialization sequence sets it to 2 logical lines of 8 chars even though there is only 1 physical line of chars. IIRC, this was specified by the manufacturer although over the years, we used several different manufacturers and all were the same. According to the 44780 datasheet it has to do with the duty factor of the LCD glass drivers 1/8 vs. 1/16 for the ones I used.

    Good luck.
     
  8. JMark

    Thread Starter New Member

    Mar 3, 2014
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    So new 16x1 displays are not setup this way?
     
  9. JMark

    Thread Starter New Member

    Mar 3, 2014
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    from what I read of people with similar problems is that the OLD 16x1 displays had three chips on them and would address 1-16 characters and that the NEWER 16x1 have a single chip and have the 8x2 character mapping. If this is correct then a new 16x1 should be a drop in replacement for my needs. Can anyone confirm this?

    http://www.microchip.com/forums/m61845.aspx
     
  10. JohnInTX

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    Jun 26, 2012
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    My 8x2 formatted ones have 1 44780 chip. The earliest date code I see is 1991. Newer ones are the same FWIW.
     
    Last edited: Mar 7, 2014
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I have both types in 16x1 displays, from my experience the older ones use the two rows of 8 char addressing. And are mainly non-backlit displays.

    I doubt it depends on the number of chips, it is how they hooked up the wires between the 44780 chip and the LCD matrix (like JohnInTX said earlier).
     
  12. JMark

    Thread Starter New Member

    Mar 3, 2014
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    Following up...I bought a new 16x1 from ebay and it worked just fine in this older machine.
     
  13. THE_RB

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    Congrats on getting a solution!

    And thank you for posting a follow up so we know what happened. :)
     
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