PXA270 WinCE LCD shutdown query

Hi all,

I'm working with a PXA270 driving a small LCD, running CE 5, and we're trying to get the transition to deep sleep mode to look nice, rather than having the screen left with a nasty residual image.

LCD datasheets all recommend outputting a few frames of completely black or white data, but I can't think of any way around this without filling the frame buffer and somehow forcing windows to re-paint the screen on resume. Nasty.

I'm guessing that just disabling the LCD controller will stop it outputting anything at all, and so the LCD will be as stuck as it would be if you just disabled it or removed power.

Anybody got any bright ideas on this one?

Thanks and best regards,


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Can you change the colour depth of the screen on the fly and can you change the frame pointer to point to a frame buffer elsewhere? If you can change the frame pointer then you can point to a black/white frame buffer in memory and leave the original screen intact. You won't need that memory because you'll be asleep. If you can change the resolution then you can reduce the colour depth to 1 bit per pixel and dramatically reduce the size of the frame buffer. You can then reverse this on power up and get your screen back very quickly.

Another (probably very tricky) way would be to store the 50 pixels or so in front of where the frame buffer is reading and temporarily replace them with black pixels. Put them back once the scan has passed Thus the screen goes black but the frame buffer still holds your original image. Timing on this would be a bit horrific but, if all you are doing is waiting to sleep and can dedicate the processor to doing it then you might be able to continually read the frame pointer faster than it is moving through the memory. This assumes a lot though. Caching could interfere, pointer might not move linearly, reading the pointer may alter its behaviour, etc. All good fun.

Alternatively, how much brightness/backlight control do you have? You might be able to turn off the backlight or dim to 0% before entering deep sleep and avoid messing with the frame buffer at all.

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Tom Lucas


See the thread entitled "PXA270 and Marvell" in this newsgroup.

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