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PICList Thread
'[OT] Cheap Graphical LCD Source Needed'
1999\02\04@024226 by William Chops Westfield

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   I just got a new All electronics catalog today and they have 640x480 LCD
   panels with on board drivers. 6"x4.5" veiwing area for 25 bux

On board drivers are not the same as an on-board controller.  (your standard
hitachi ascii display has both, right?)  A VGA LCD with drivers needs
something analagous to an expensive VGA card to give it dot-addressable or
text capabilities.  (You could probably do SOMETHING with just a PIC, but
it'd be as hard as driving video directly, I think.)

BillW

1999\02\04@085947 by ryan pogge

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so can these LCD's  be hooked directly to a computer with no modification?


>    I just got a new All electronics catalog today and they have 640x480
LCD
>    panels with on board drivers. 6"x4.5" veiwing area for 25 bux
>
>On board drivers are not the same as an on-board controller.  (your
standard
>hitachi ascii display has both, right?)  A VGA LCD with drivers needs
>something analagous to an expensive VGA card to give it dot-addressable or
>text capabilities.  (You could probably do SOMETHING with just a PIC, but
>it'd be as hard as driving video directly, I think.)
>
>BillW

1999\02\04@152721 by John Payson

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|>    I just got a new All electronics catalog today and they have 640x480
|LCD
|>    panels with on board drivers. 6"x4.5" veiwing area for 25 bux
|>
|>On board drivers are not the same as an on-board controller.  (your
|standard
|>hitachi ascii display has both, right?)  A VGA LCD with drivers needs
|>something analagous to an expensive VGA card to give it dot-addressable or
|>text capabilities.  (You could probably do SOMETHING with just a PIC, but
|>it'd be as hard as driving video directly, I think.)

|so can these LCD's  be hooked directly to a computer with no modification?

Normally not.  A special type of display controller is needed
because the LCD's have some significant differences vs video
displays:

[1] Most VGA-sized passive-matrix LCD's use a "dual-scan" design;
   they are basically wired as two half-height displays stacked
   on top of each other.  Thus, the hardware needs to be able to
   feed out lines 0 and 240 at the same time, then lines 1 and
   241, etc.  Most video cards just read out one row at a time
   rather than two rows separated by 240 pixels.

[2] Most displays have a shift-register design which takes in a
   group of eight pixels at a time (for each half of the display).
   For monochrome this probably isn't too bad, but a color display
   is simply a 1920-pixel-wide display with color filtering applied
   to the pixels.  Thus, the first three bits of the first byte
   control the first pixel's RGB, the next three bits control the
   next pixel's RGB, and the last two bits of that byte along with
   the first bit of the next byte control the third pixel, etc.
   You'd probably want to have something to resequence the data to
   avoid having to do store bitmaps strangely in memory.

[3] The displays do not have any inherent gray-scale or continuous-
   color abilities.  Instead, for a pixel to be 3/4 dark it needs
   to be turned dark for three frames out of every four.  To avoid
   display flicker, adjacent pixels are usually "phased" different-
   ly; this works well, but adds to the hardware requirements.

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