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Operation in Greyscale mode

The S128240[C/D] display uses the Sitronix ST7529 controller.
This controller is capable of 5-bit-grey-scale operation.
E.g. instead of just having a pixel on/off, the shade of the pixel could be set to 30 grey values in addition to the basic 'on/off'.
I'm wondering whether the S128240 display and nematic is designed to work with this feature of the controller?
I'm asking this as when I tested the feature with the standard init_LCD(), I noted two anomalies.
1) The display was severely 'streaked' in columns which also contained 'grey'
2a) When ~30%of the display is set to grey, the charge pump can't keep-up
2b) When ~10% of the display is set to grey, and there is significant black on the display, the charge pump can't keep up.
TEST1 - PASS
Clear screen (write 0x00 to each pixel)
Print a line of text in 100% intensity at the top of the screen I.e. writing 0xff to each 'on' pixel
Paint a 32 x 240 graphic in 100% intensity (black) at the top of the screen I.e. writing 0xff to 'on' each pixel
RESULTS: The graphic and text were clear, distinct with uniform pigmentation.
TEST2 - FAIL
Repeat test 1, keeping 100% intensity of the text, but changing the graphic to 75% intensity I.e. writing 0xc0 to each 'on' pixel
RESULTS: The graphic was banded, and faint, text was streaked where the graphic was most intense.
This test was repeated at several other intensity settings, all with the same result.
TEST3 - PASS
Clear screen (write 0x00 to each pixel)
Print a line of text in 100% intensity at the top of the screen I.e. writing 0xff to each 'on' pixel
Paint three instances of a 64 x 64 solid block in 100% black across the center-line of the screen (12 pixels between each block laterally)
RESULTS: The graphic and text were clear, distinct with uniform pigmentation.
TEST4 - FAIL
Repeat test3, keeping 100% intensity for the text, but changing the blocks to 75% intensity
RESULTS: All of the display faded-out. The text was streaked (fading out in the same columns as the blocks).
Note, the text used was from a 5 wide x 12 high font.
To summarize
1) Can the S128240 be operated in 'grey-scale'
2) Are there any optimizations to the LCD_init required for this?

Replies

dtechsupport's picture
dtechsupport
July 16, 2009

Did you ever trying by-passing the charge pump and using greyscale? The S128240D should be able to handle greyscale, however the charge pump is always going to be the weak link is a display of this size, probably not so much of an issue on the S128240C.