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LCD Display issues — Parallax Forums

LCD Display issues

SteveWoodroughSteveWoodrough Posts: 190
edited 2012-11-07 22:12 in Accessories
Hello,
I have Rev E 2 x16 non back lit LCD that suddenly quit working. The display shows dark blocks along the top row and nothing across the bottom row.
The test mode only works if I apply power to the center pin and ground the data RX pin, and turn up the display contrast. Is the display dead? Is there some way to reset the display?

Thank You

Steve

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2012-11-03 21:36
    If the test mode works, then the display should work if it's wired correctly. The test mode exercises pretty much everything in the display except the RX pin itself. See the documentation for details. Also make sure the Baud switches are set correctly when you take it out of test mode. In test mode, the RX pin is ignored.
  • SteveWoodroughSteveWoodrough Posts: 190
    edited 2012-11-04 07:06
    Mike,
    Thank you for your reply. This situation is a bit of a paradox since the test mode works, but only if the display is wired incorrectly.

    Here is the a description of the setup. Only 2 wires are used, 5V and GND. NO signal is used for the time being. Both DIP switches OFF.

    If I apply 5V and GND to the correct pins on the display I get the top row black blocks I described.

    If I apply 5V to the correct pin and GND to the RX pin the the Test message is displayed and the little PAC man eats the letters.

    Is it possible the firmware is corrupted somehow? I try to be careful, but it is possible I mis connected the display at some point. Is it possible to damage the unit with only 5V applied to the wrong pin?

    Regards,
    Steve







    With regard to test mode, if I provide 5V
  • Mike GreenMike Green Posts: 23,101
    edited 2012-11-05 07:38
    What you describe doesn't make sense to me. It's not possible for the firmware to be corrupted without deliberately trying to change it. You can certainly damage the unit (destroy it) by connecting the power incorrectly, usually by connecting ground to the +5V pin and +5V to the ground pin. I suggest you call Parallax tech support. Have you adjusted the contrast correctly? That could produce the "black blocks" when the power is connected correctly.
  • xanaduxanadu Posts: 3,347
    edited 2012-11-06 21:07
    I also read somewhere sending data to it with the +5v disconnected is bad... So you could have put +5 on the RX pin while ground was connected? Or your power source wasn't enough and you sent data to it?

    Rev E CAUTION
    DO NOT PROVIDE A SIGNAL TO THE 'RX' PIN BEFORE APPLYING 5 VDC TO THE '5V' PIN.     PDF (last page)

    Could that trash the RX pin but allow the rest to work?
  • Mike GreenMike Green Posts: 23,101
    edited 2012-11-07 13:49
    Any time you apply a signal to a device without applying power, you run the risk of damaging the device. If you're lucky, you may just blow out a protective (substrate) diode. If you're unlucky, you may do some damage deeper in the device. It's certainly possible you could have destroyed the input circuitry for the RX pin while the rest of the device is fine. It's difficult to tell without more information on the details of the device, in this case the LCD controller.
  • xanaduxanadu Posts: 3,347
    edited 2012-11-07 22:12
    That would explain why only test mode works right? I don't want to try it on mine lol.
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