Very simple: Need help making sense of a HD44780 equivalent datasheet.

Discussion in 'Electronics Resources' started by Gump, Jul 27, 2010.

  1. Gump

    Thread Starter Member

    Jun 7, 2010
    57
    1
    Hi,

    I've found a 20x4 LCD screen, the PC2004A by Powertip, their datasheet is quite rubbish really although from what I gather it is the equivalent of the HD44780 controller (Edit: No, the actual controller used is a ST7066U, a completely different animal), but I'm having a couple of issues understanding the powertip datasheet:

    http://www.farnell.com/datasheets/355527.pdf

    I understand the "Pin Assignments", but get a little confused when it comes to the "Absolute Maximum Ratings" and the "Electrical Characteristics" sections.

    1) When they say "Vdd-Vss", are they meaning the voltage of Vdd (+ve supply) in relation to Vss (GND)?

    2) They then mention the LCD driving supply voltage as being "Vdd-Vee", but I can't see a Vee pin at all? Although it seems that Vee means GND also, but why did they use Vee rather than Vss?

    3) There doesn't seem to be a Vin pin at all listed in the "Pin Assignments" despite being mentioned as the "Input Voltage".

    4) Under the electrical characteristics the "LCD Operation Voltage" uses the symbol Vop, again there isn't a Vop symbol, should the Vo symbol in the "Pin Assignments" actually be Vop?

    5) What do the N W symbols mean?

    6) The sheet keeps mentioning -0.3V as a minimum, how exactly could things work with such a low negative voltage?

    Thank you,
    Gump.
     
    Last edited: Jul 27, 2010
  2. tom66

    Senior Member

    May 9, 2009
    2,613
    213
    1) Correct. All voltages are usually given wrt (with respect to) ground or Vss. If this is not the case, it is usually mentioned.

    2) Vee = voltage emitter-emitter. The chip probably has a bipolar-CMOS design incorporating NMOS/PMOS and NPN/PNP transistors. The Vee voltage may be negative, for driving the LCD.

    3) Vin = Input voltage range for any IO pin.

    4) Vop = Possibly the output voltage. Vo is the same.

    5) Unsure.

    6) That's the absolute minimum tolerable voltage, either on the input or on the IO. Putting a voltage lower than this could cause damage to the chip. The chip will not function at this voltage.
     
    Gump likes this.
  3. Gump

    Thread Starter Member

    Jun 7, 2010
    57
    1
    Excellent thank you. :)
     
  4. n1ist

    Active Member

    Mar 8, 2009
    171
    16
    On this data sheet, they are calling the contrast voltage Vee in some places and Vo or Vop in others. They mean that the voltage on pin 3 ranges between 13 volts and 0 volts below Vdd. The voltage range you need is temperature dependent, and appears to be between (5-4.4) = 0.6v and (5-7.9) = -2.9v with respect to ground for a 5v supply, For a 3.3v supply, that would be (3.3-4.4) = -1.1v and (3.3 - 7.9) = -4.6v.

    The N and W headings in the contrast section probably refer to a Narrow or Wide viewing angle.
     
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