STMicroelectronics STM32F405 Reference Manual page 360

Chrom-Art Accelerator™ controller (DMA2D)
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ALPHA[7:0]
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Bits 31:24 ALPHA[7: 0]: Alpha value
Bits 23:18 Reserved, must be kept at reset value
Bits 17:16 AM[1: 0]: Alpha mode
Bits 15:8 CS[7: 0]: CLUT size
Bits 7:6 Reserved, must be kept at reset value
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CS[7:0]
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These bits define a fixed alpha channel value which can replace the original alpha value
or be multiplied by the original alpha value according to the alpha mode selected
through the AM[1:0] bits.
These bits can only be written when data transfers are disabled. Once a transfer has
started, they become read-only.
These bits select the alpha channel value to be used for the foreground image. They
can only be written data the transfer are disabled. Once the transfer has started, they
become read-only.
00: No modification of the foreground image alpha channel value
01: Replace original foreground image alpha channel value by ALPHA[7: 0]
10: Replace original foreground image alpha channel value by ALPHA[7:0] multiplied
with original alpha channel value
other configurations are meaningless
These bits define the size of the CLUT used for the foreground image. Once the CLUT
transfer has started, this field is read-only.
The number of CLUT entries is equal to CS[7:0] + 1.
DocID018909 Rev 11
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Reserved
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START
Reserved
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CCM CM[3:0]
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RM0090
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AM[1:0]
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1 0
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