two questions about mcu - analog vs digital comparator & lcd segments

Discussion in 'Embedded Systems and Microcontrollers' started by aamirali, Apr 4, 2013.

  1. aamirali

    Thread Starter Member

    Feb 2, 2012
    1. In some MCU , it is writen that they have digital or anlog converter. What is diff b/w two.
    In analog comparator can I use sine wave also. or what.

    2. Also some mention that they have lcd controller. I think they don't about 16x2 lcd which we use generally. What lcd controller they have.

    & What does segment mean here like 40x4 segment display.
  2. MrChips


    Oct 2, 2009
    None of your inquiries make any sense. You will have to post the information that you find confusing.
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    One would be digital to analog converter: an output, put a number in, get a voltage out.
    Other would be analog to digital converter: input, put a voltage in, get a number out.

    Yes you can put a sine wave in, and the output will change if part of the wave crosses the reference voltage input. It is the same as any analog comparator, though they are usually very basic circuits.

    Correct as far as I know. The LCD they control have individual segments or pixels that need to be driven with square waves. Example: each segment of a 7-segment number on the display needs a separate control line.

    The "16x2" types just need 6 or so logic outputs to control by sending data with control signals.

    40x4 means how many characters are on the display, this means 4 lines of 40 characters (a rather large display). "segment" doesn't really apply to these.
  4. JohnInTX


    Jun 26, 2012
    PICs with a segmented type LCD controller are specified like the 40x4 the OP stated. In this case, 40x4 refers to 40 segments and 4 commons (backplanes) which can drive a maximum of 160 elements (segments) on a segment-type LCD display (not our usual 5x7dot matrix LCD displays, its a completely different animal).

    Displays of this sort are just a bunch of addressable segments of any shape including segments that can make 7-segment numerics but also with the ability to have icons or other symbols, each of which is 1 'segment'. While not as good for text display, they are good when symbols, logos etc are incorporated into the (frequently custom) LCD display glass.

    The pictures are a good example. Some 7-segment numerics with symbols and pictures. Each digit takes 7 of the LCD segments, each symbol (or part of symbol, like the increasing clouds) takes one segment. On your 40x4 PIC, you get up to 160 of them to mix, match and create symbols and digits.

    To get the maximum number of segments requires analog voltage multiplexing, Static, 1/2 , 1/3 or 1/4 which nominally corresponds to the number of backplanes (commons) on the display. Which configuration is used is determined by the display glass itself and is part of the display design. The PIC LCD controller is configured to match the glass. You have to know what the display glass needs but once configured, the LCD controller takes care of all of the display refresh. Some of the later PICs can keep the LCD refreshed even while the processor is sleeping.

    From the programmer's point of view, there is a bit-addressable array of bytes in RAM. Set a bit and its corresponding LCD segment turns on. Easy enough but one of the challenges is that there are no decoded digits etc. To display a 7 segment number, you have to rummage through the bit array and flip the particular bits that are hooked to each of the segments that comprise the digit(s).

    Look around at Microchip's offerings for segmented LCDs, pick one and look at the datasheet section on LCD controller. The second image is of the PICDEM LCD 2 demo board and shows a custom LCD glass with 7 segment digits and other icons/symbols addressed via the bit-addressable RAM array in the PIC.
    Last edited: Apr 5, 2013
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