ST STM32F405 Reference Manual page 506

LCD-TFT controller (LTDC)
Bits 31:3 Reserved, must be kept at reset value
Bits 2:0 PF[2:0]: Pixel Format
16.7.19 LTDC Layerx Constant Alpha Configuration Register (LTDC_LxCACR)
(where x=1..2)
This register defines the constant alpha value (divided by 255 by Hardware), which is used
in the alpha blending. Refer to LTDC_LxBFCR register.
Address offset: 0x98 + 0x80 x (Layerx -1), Layerx = 1 or 2
Reset value: (Layerx -1) 0x0000 00FF
31 30 29 28
15 14 13 12
Bits 31:8 Reserved, must be kept at reset value
Bits 7:0 CONSTA[7:0]: Constant Alpha
16.7.20 LTDC Layerx Default Color Configuration Register (LTDC_LxDCCR)
(where x=1..2)
This register defines the default color of a layer in the format ARGB. The default color is
used outside the defined layer window or when a layer is disabled. The reset value of
0x00000000 defines a transparent black color.
Address offset: 0x9C + 0x80 x (Layerx -1), Layerx = 1 or 2
Reset value: 0x0000 0000
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These bits configures the Pixel format
000: ARGB8888
001: RGB888
010: RGB565
011: ARGB1555
100: ARGB4444
101: L8 (8-Bit Luminance)
110: AL44 (4-Bit Alpha, 4-Bit Luminance)
111: AL88 (8-Bit Alpha, 8-Bit Luminance)
27 26 25
11 10 9
Reserved
These bits configure the Constant Alpha used for blending. The Constant Alpha is divided
by 255 by hardware.
Example: if the programmed Constant Alpha is 0xFF, the Constant Alpha value is
255/255=1
24 23 22 21
Reserved
8 7 6
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RM0090 Rev 18
20 19 18
5 4 3 2
CONSTA[7:0]
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RM0090
17 16
1 0
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