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matter with some special definition

billy nguyen
Intellectual 290 points
Other Parts Discussed in Thread: MSP430FG4618

Hi guys,

When i read datasheet relating to LCD_A of kit MSP430FG4618, i had some matter of definition. Those are "fractional LCD biasing voltage" and "charge pump". what are they? Can you explain it for me?

Thank you so much,

Billy nguyen

  • 0
    Guru 227245 points

    Other than LED, where you simply press a current through a diode, so it emits light, LCDs require a way more complex control. Hoever, it' snot the current that makes an LCD segment show or hide, it's teh applied voltage, which has to constantly change and invert, and also controls the contrast.

    The charge pump generates the required voltages for an LCD from MSPs VCC. This includes negative voltages (in relation to the LCD GND level, which does not necessarily need to be the MSP GND level). adn voltages which are higehr than the MSP supply voltage.

    The fractional LCD biasing voltage refers to the mechanism that makes the LCD segmens seeing pisitive and negative voltages of diferent height. If you set the LCD segment to a 'GND' level of, say 1V, then any voltage below 1V appears to be negative, 1V appears to be 0V and so on. The LCD_A allows for setting different biasing voltages based on the fractional voltages that are generated from VLCD, either internally (when the charge pump i sused) or externally. Using a different bias voltage changes the contrast and viewing angle of the LCD.

  • 0 in reply to Jens-Michael Gross
    Intellectual 290 points

    Thanks Jens,

    I got your ideas. But, when I feel so difficult program, you have any example codes for LCD_A? would you please send me? 

     

  • 0 in reply to billy nguyen
    Guru 227245 points

    Sorry, I never worked with the internal LCD modules (and even if, my code belongs to my company, so I couldn't post it anyway)
    However, most of the stuff is done internally. YOu only have to configure what you have: common or 2,3,4x multiplexed display, internally generated or external LCD voltage and the basic timer for the timing (the values are not too critical, wrong timings will make the LCD look pale or only visible form a small angle, but usually will not prohibit it completely.

    Once the setup is done, chnging th edisplay is easy - just set the bits in memory which you want to have shown on the display.

    The tricky part then is to find an algorithm that sets the proper bits you you'll see what you intended.

    I think in the forum are some references to demo software. Also, TI has some example projects, e.g. for the experimenters boards with LCD or the Chronos watch. At least for the init and the basic workings, you can look there (the display segments and therefore the correct mapping will most likely be different to yours)

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