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LCD-embedded controller or separate controller

Discussion in 'Embedded' started by Ajab, Aug 13, 2007.

  1. Ajab

    Ajab Guest

    what are the pros and cons for using embedded LCD controller and
    separate LCD controller?
     
    Ajab, Aug 13, 2007
    #1
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  2. Ajab

    Ajab Guest

    embedded inside a microcontroller. forgot to mention.
     
    Ajab, Aug 13, 2007
    #2
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  3. Ajab

    Tom Lucas Guest

    Seperate controllers take up more board space. However, they mean you
    can use a simpler microcontroller which will cost less than one with a
    built in controller. Whether the saving on the MCU pays for the cost of
    the external controller is a question of production quantities.

    A point I suspect more valid to you is that there are relatively few
    microcontrollers with built in LCD controllers so you narrow the number
    of devices to choose from. An external controller makes many more
    available.

    Bearing in mind your previous question about GUIs then I suspect you are
    still in a preliminary stage in specifiying your system. I recommend a
    MCU with a built in controller - I like the Sharp (soon to be NXP)
    parts. Get a development kit with an LCD panel and you'll save yourself
    a lot of effort (LogicPD are good). If cost is an issue then think hard
    about whether you can complete this project - it's hard to do LCDs on
    the cheap.
     
    Tom Lucas, Aug 13, 2007
    #3
  4. Ajab

    Ajab Guest

    Is there specific/standard pinout for LCDs? I was searching for same,
    but I can see different LCDs have different pinouts. I have many LCDs
    available with the required specification. How do I choose one?
     
    Ajab, Aug 13, 2007
    #4
  5. Ajab

    larwe Guest

    Integrated controllers almost invariably use UMA, which has
    performance implications.
     
    larwe, Aug 13, 2007
    #5
  6. Ajab

    Tom Lucas Guest

    That is very true. My system runs 64K colours at 640x480 resolution and
    running code from flash causes significant screen jitter. I have to copy
    into RAM and run from there or drop to 256 colours. To maintain a 50Hz
    refresh rate something like 30% of my processor bandwidth is taken up
    with just keeping the screen refreshed. At 75Hz it takes nearly half of
    it.
     
    Tom Lucas, Aug 13, 2007
    #6
  7. Ajab

    Tom Lucas Guest

    There are many. Don't base your screen choice on the connector alone but
    it would be nice if you had a second choice that was compatible with the
    first. There are more important things in choosing a screen - cost,
    brightness, contrast, cost.
     
    Tom Lucas, Aug 13, 2007
    #7
  8. It depends on the Design w.r.t Size, Cost factor , the Type of
    Application/Product and Use.

    Karthik Balaguru
     
    karthikbalaguru, Aug 14, 2007
    #8
  9. Though the pinouts & naming conventtions look bit different. The core
    cocept of Driver here will be the same and simple.

    Karthik Balaguru
     
    karthikbalaguru, Aug 14, 2007
    #9
  10. Ajab

    Ajab Guest

    I haven't read much theory about LCDs. What I know is there are many
    LCD types.(active, passive) then TN,TNR,STN,FSTN,TFT,TFD,etc. How do I
    know which is suitable for me? Do I need to study all of these??? :-(
     
    Ajab, Aug 16, 2007
    #10
  11. Ajab

    Tom Lucas Guest

    It depends what your device is doing. TFT gives good all round quality
    but STN is a bit cheaper. If you just want grayscale then TFT is a waste
    of time. If you want things that are readble in sunlight then you need
    to start thinking about transflective screens and the like - I've seen
    some good Hitachi ones demonstrated.

    If you are going to buy a reasonable quantity (100+) then get a rep to
    come in a demonstrate some of their models. The best way to decide is to
    see the image for yourself. And then look at the price and see what you
    can afford. Don't forget to factor in the price of inverters, connectors
    and/or cabling.
     
    Tom Lucas, Aug 16, 2007
    #11
  12. Ajab

    robert Guest

    You may find that your required resolution will drive whaqt technologies
    you can use. If you need graphics under 320x240 and you are not looking
    for color there are planty of STN and DSTN options. When you get to QVGA
    (320x240 pixels) TFT displays are taking over in price and number
    available.

    When my team was considering display and controller options we found
    that the memory requirements for larger displays was a serious
    consideration and I would recommend if you are looking at VGA (640x480)
    resolutions you use a separate controller with its own memory bus
    because even at only 16-bit color (8-bit actually uses as much
    processing overhead since it requires a color lookup table that is note
    required by most video controller for 16-bit color) every framebuffer is
    going to require 640x480x2 bytes of RAM (600KB). This doesn't sound like
    a lot, but you need at least two framebuffers so one can be displayed
    and one can be updated. Some separate video controllers have their own
    dedicated RAM and only need a full framebuffer loaded occasionally when
    there is a full screen update. On-board video controllers may not have
    this feature and instead require interleaving memory accesses of the
    framebuffers with other bus activity and consequently slow things down
    at a rate that depend on the display refresh frequency and display size
    (resolution). My team eventually selected the Freescale 5329 Coldfire
    processor and we are using the on-board video controller to drive a
    320x240 color display for an industrial machine controller design. The
    controller was capable of driving TFT and STN technologies of
    resolutions up to 800x600 with 18-bit color, but like I said that is at
    the expense of processor performance elsewhere so our balance ended up
    at 320x240 16-bit color.

    If your product can afford the extra $30+ in cost (video controller +
    dedicated video RAM) and video is an important feature, you probably
    want a separate controller. If you simply need graphics and integrated
    controller might work. Our design with the Freescale part is working out
    but I have heard of problems from other groups using other processors
    with a similarly built-in controller where they ended up using an
    external controller anyway. I'm not sure what the issues were in those
    cases but you can see the trade offs we considered.
     
    robert, Aug 19, 2007
    #12
  13. Ajab

    Ajab Guest

    Can anyone give me any application notes which will help me to
    understand the uC and LCD (or uC and LCD controller) interfacing ?
     
    Ajab, Aug 21, 2007
    #13
  14. Ajab

    CBFalconer Guest

    Can anyone explain why this query required quoting roughly 115
    lines of former conversation? Or why it was posted as a reply in
    this thread?
     
    CBFalconer, Aug 21, 2007
    #14
  15. Ajab

    Ajab Guest

    ok ...I have put a new query... :eek:)
    If you have some application notes, you can post there.
     
    Ajab, Aug 21, 2007
    #15
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