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Topics - durian

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TFTs / Reading display memory
« on: August 06, 2015, 06:15:25 PM »
I've been using an NHD-2.4-240320SF-CTXI-1 in a product for a few years now. I can write to the display using a 16-bit parallel bus without any problem. The display shows what it should. However, I've never been able to read the memory correctly. This hasn't been critical for us, but I decided to dig into it a bit today.

It appears when I write 16-bits, I read the data back in a 24-bit format. For example, if I write:
0001 fffe
I read back:
0000 08fc fcf4

It looks like RGB 565 packing:
Write (binary):
rrrrrggggggbbbbb rrrrrggggggbbbbb
Read (binary):
rrrrrXXXggggggXX bbbbbXXXrrrrrXXX ggggggXXbbbbbXXX

The X's are typically 0, but not always. Sometimes the highest order X bit in the R and B values is a 1. I'm not sure what the pattern is.

Does anyone have any ideas why I'm getting this asymmetric  read/write behavior?

Thanks,
mike



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