B69000 Asiliant Technologies, B69000 Datasheet - Page 342

• Manufacturer Part Number: B69000
• Manufacturer: Asiliant Technologies

Specifications of B69000

• Lead Free Status / Rohs Status: Supplier Unconfirmed

BitBLT Operation
E-7
Per-Pixel Write Masking
The BitBLT engine is able to perform per-pixel write-masking with various data sources used as pixel masks
to constrain which pixels at the destination will actually be written to by the BitBLT engine. As shown in the
figure below, either monochrome source or monochrome pattern data may be used as a pixel mask, but not
color source or color pattern. Another available pixel mask called “color transparency” is derived by
comparing a particular color to either the color already specified for a given pixel at the destination or the
color that results from the bit-wise operation performed for a given pixel.
Figure E-2: Block Diagram and Data Paths of the BitBLT Engine
Bits 13 and 17 of BR04 are used to select either the monochrome source or the monochrome pattern data
as a pixel mask. When this feature is used, the bits in either the monochrome source or the monochrome
pattern data that carry a value of 0 cause the bytes of the corresponding pixel at the destination to not be
written to by the BitBLT engine, thereby preserving whatever data already residing within those bytes. This
feature can be used in writing characters to the display in a way that preserves the pre-existing backgrounds
behind those characters.
Bits 14 through 16 of BR04 are used to select and enable 1 of 4 forms of per-pixel write-masking, each using
a different color comparison as a mask. Bit 14 is used to enable this function. Bit 15 chooses between two
different comparisons of color values. Depending on the setting of bit 15, a comparison is made between
a key color (carried by either BR01 or BR09) and either the color already specified in the bytes for each of
the pixels at the destination or the color resulting from the bit-wise operation being performed for each pixel.
Bit 16 chooses whether the overwriting of the bytes at the destination will occur when the two compared
values are found to be equal or when they are found not to be equal.
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69000 Databook
Subject to Change Without Notice
Revision 1.3 8/31/98