STMicroelectronics STM32F405 Reference Manual page 506

LCD-TFT Controller (LTDC)
Note: The Constant Alpha value, is the programmed value in the LxCACR register divided by 255
by hardware.
Example: Only layer1 is enabled, BF1 configured to Constant Alpha
BF2 configured to
Constant Alpha: The Constant Alpha programmed in the LxCACR register is 240 (0xF0).
Thus, the Constant Alpha value is 240/255 = 0.94
C: Current Layer Color is 128
Cs: Background color is 48
Layer1 is blended with the background color.
BC = Constant Alpha x C + (1 - Constant Alpha
16.7.22 LTDC Layerx Color Frame Buffer Address Register (LTDC_LxCFBAR)
(where x=1..2)
This register defines the color frame buffer start address which has to point to the address
where the pixel data of the top left pixel of a layer is stored in the frame buffer.
Address offset: 0xAC + 0x80 x (Layerx -1), Layerx = 1 or 2
Reset value: 0x0000 0000
31 30 29 28
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15 14 13 12
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Bits 31:0 CFBADD[31:0]: Color Frame Buffer Start Address
16.7.23 LTDC Layerx Color Frame Buffer Length Register (LTDC_LxCFBLR)
(where x=1..2)
This register defines the color frame buffer line length and pitch.
Address offset: 0xB0 + 0x80 x (Layerx -1), Layerx = 1 or 2
Reset value: 0x0000 0000
31 30 29 28
Reserved
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15 14 13 12
Reserved
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506/1731
Constant Alpha
1 -
27 26 25
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11 10 9
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These bits defines the color frame buffer start address.
27 26 25
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11 10 9
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DocID018909 Rev 11
x Cs = 0.94 x 128 + (1- 0.94) x 48 = 123.
)
24 23 22 21
CFBADD[31:0]
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8 7 6 5
CFBADD[31:0]
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24 23 22 21
CFBP[12:0]
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8 7 6 5
CFBLL[12:0]
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20 19 18 17
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4 3 2 1
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20 19 18 17
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4 3 2 1
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RM0090
16
rw
0
rw
16
rw
0
rw