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From: azraiyl on 3 May 2010 11:06
To display pixels on a TFT hsync/vsync is used. But when the displayed
image does not change do I still have to update the TFT regularly? I like
to save the precious bus bandwidth for other things (there is no dedicated
framebuffer available with its own memory).

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From: larwe on 3 May 2010 11:24
On May 3, 11:06 am, "azraiyl" <azraiyl(a)n_o_s_p_a_m.gmail.com> wrote:
> To display pixels on a TFT hsync/vsync is used. But when the displayed
> image does not change do I still have to update the TFT regularly? I like

You most definitely do. The LCD will go blank within 1 frame period or
less if you stop supplying data.

If you need a static image without refresh, you need an e-ink type
display. All LCD technologies require constant refresh. You could
consider an LCD with on-board controller and frame buffer, and maybe
SPI or I2C interface (but of course, you lose performance in the
interface bottleneck).
From: azraiyl on 3 May 2010 12:43
Just to better understand it. For STN like displays the capacitor can't
store the information long enough (therefore constant refresh is a must).
But on TFT LCDs there is a transistor for each pixel AFAIK, which should
store this information.

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From: Didi on 3 May 2010 13:00
On May 3, 7:43 pm, "azraiyl" <azraiyl(a)n_o_s_p_a_m.gmail.com> wrote:
> Just to better understand it. For STN like displays the capacitor can't
> store the information long enough (therefore constant refresh is a must).
> But on TFT LCDs there is a transistor for each pixel AFAIK, which should
> store this information.    

The transistor relies on its gate capacitance to store that
information;
this capacitance gets discharged because of leakage.
What happens to a TFT when you stop to refresh it is it loses its
image,
goes through sort of rainbow colours to totally white IIRC (it's been
years since I last saw this because of error or experiment :-) ).
So you may not lose the image on the next frame as larwe suggests, but
within
a second or so you will. And you will certainly at least begin to lose
image quality on the very next frame.

Dimiter

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Dimiter Popoff Transgalactic Instruments

http://www.tgi-sci.com
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http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/



From: larwe on 3 May 2010 13:08
On May 3, 12:43 pm, "azraiyl" <azraiyl(a)n_o_s_p_a_m.gmail.com> wrote:

> But on TFT LCDs there is a transistor for each pixel AFAIK, which should
> store this information.    

A transistor is not a flip-flop. The purpose of the transistor is to
provide local amplification of the drive signal, so it is not subject
to the capacitance of a long row or column.
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