M69000 Asiliant Technologies, M69000 Datasheet - Page 337

• Manufacturer Part Number: M69000
• Manufacturer: Asiliant Technologies

Specifications of M69000

• Lead Free Status / Rohs Status: Supplier Unconfirmed

E-2
BitBLT Operation
Color Depth Configuration and Color Expansion
The graphics system can be configured for color depths of 1, 2, 4, 8, 16, 24, and 32 bits per pixel, while the
BitBLT engine is intended to work only with graphics data having a color depth of only 8, 16, or 24 bits per
pixel. It is assumed that the BitBLT engine will not be used when the graphics system has been configured
for a color depth that the BitBLT engine was not designed to support. In theory, it is possible to configure
the BitBLT engine and graphics system for different color depths, but this is not recommended.
The configuration of the BitBLT engine for a given color depth dictates the number of bytes of graphics data
that the BitBLT engine will read and write for each pixel while performing a BitBLT operation. It is assumed
that any input destination data from the frame buffer will already be at the color depth to which the BitBLT
engine is configured. Similarly, it is assumed that any source or pattern data used as an input will have this
same color depth, unless one or both is monochrome. If either the source or pattern data is monochrome,
the BitBLT engine will perform a process called “color expansion” to convert such monochrome data to color
at the color depth to which the BitBLT engine has been set.
During “color expansion” the individual bits of monochrome source or pattern data that correspond to
individual pixels are converted to 8, 16, or 24 bits per pixel (i.e., 1, 2, or 3 bytes per pixel -- whichever is
appropriate for the color depth to which the BitBLT engine has been set). If a given bit of monochrome
source or pattern data carries a value of 1, then the byte(s) of color data resulting from the conversion
process will be set to the value of a specified foreground color. If a given bit of monochrome source or
pattern data carries a value of 0, the resulting byte(s) will be set to the value of a specified background color.
The BitBLT engine is configured for a color depth of 8, 16, or 24 bits per pixel through either bits 5 and 4 of
XR20, or bits 25 and 24 of BR04, depending upon the setting of bit 23 of BR04. Whether the source and
pattern data are color or monochrome must be specified using bits 12 and 18, respectively, of BR04. The
foreground and background colors for the color expansion of both monochrome source and pattern data
may be specified using BR02 and BR01, respectively. Alternatively, if bit 27 of BR03 is set to 1, the
foreground and background colors used in the color expansion of monochrome source data may be
independently specified using BR0A and BR09, respectively.
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69000 Databook
Subject to Change Without Notice
Revision 1.3 8/31/98