Re: LCD Interface

Hi Sylvain,

"Sylvain Munaut" <com.246tNt@tnt> wrote in message
news:4314d565$0$22061$ba620e4c@xxxxxxxxxxxxxxxxx
> Hi Pierre,
>
> Pierre de Vos wrote:
>> I've been struggeling with a long standing problem driving a 320x240
>> graphic
>> LCD display. I've been using a LCD module with an Epson SED1335
>> controller
>> chip. In my application the controller is quite susceptible to noise -
>> it
>> resets for no reason, exibits distortion of the image. Googling has come
>> up
>> with some other people also having similar symptoms with this controller.
>>
>> I have mostly overcome the problem by adding additional filtering to the
>> module - extra caps, ferrite on the cable, but the problem sometimes
>> persists.
>>
>> I've been looking at using a controller-less module and driving it
>> directly
>> from the FPGA I have on the board. The problem is that the Acex 1k30 I
>> have
>> on the board only has about 24k memory bits and the memory buffer for the
>> LCD requires 76k bits (320x240).
>
> Well, or more ...
> Using temporal dithering you can achieve about 16 gray levels if you
> want. (more and it starts to flicker).
>
>
>> I've been thinking lately that maybe I can compress the memory buffer,
>> then
>> write it to the FPGA and have the FPGA uncompress the buffer spitting
>> writing the frame out to the LCD.
>>
>> Any ideas on this technique or compression techniques?
>
> What kind of stuff are you displaying ?
>
> For example if you have a user interface, maybe you can consider you
> screen as being a matrix of character to display text with some char
> being "icon".
> Imagine dividing 8x8 tiles with 256 possible chars. So the screen is
> 40x30 tiles = 1200 tiles = ~1.2 kbytes = 9.6 kbits to store what char to
> display in each tile.
> Then there is the content of the tiles themselves. With just B/W tiles,
> each tile takes 8x8 = 64bits, so you need 16kbits for the tiles memory.
> The total is 25.6 kbits, slightly above what you have but you can
> imagine only allowing to use 128 different tiles ...
>
>
> If you have real _images_ to display then you need some image
> compression, that's quite harder and there is no guarantee that the
> image you'll need to store will be compressible into what space you have.
>
>
> Sylvain
>

It's a B/W LCD 1 bit per pixel and basically I display line graphics using
an in memory frame buffer and blasting the buffer to the LCD from the CPU.

Pierre


.

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