M69000 Asiliant Technologies, M69000 Datasheet - Page 349

• Manufacturer Part Number: M69000
• Manufacturer: Asiliant Technologies

Specifications of M69000

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E-14
BitBLT Operation
To accommodate discontiguous source data, the Source and Destination Offset Register (BR00) can be
used to specify the offset in bytes from the beginning of one scan line’s worth source data to the next.
Otherwise, if the source data is contiguous, then an offset equal to the length of a scan line’s worth of source
data should be specified.
Monochrome Source Data
Bit 12 of the BitBLT Control Register (BR04) specifies whether the source data is color or monochrome.
Since monochrome graphics data only uses one bit per pixel, each byte of monochrome source data
typically carries data for 8 pixels which hinders the use of byte-oriented parameters when specifying the
location and size of valid source data. Some additional parameters must be specified to ensure the proper
reading and use of monochrome source data by the BitBLT engine. The BitBLT engine also provides
additional options for the manipulation of monochrome source data versus color source data.
The various bit-wise logical operations and per-pixel write-masking operations were designed to work with
color data. In order to use monochrome data, the BitBLT engine converts it into color through a process
called color expansion, which takes place as a BitBLT operation is performed. In color expansion, the single
bits of monochrome source data are converted into one, two, or three bytes (depending on the color depth
to which the BitBLT engine has been set) of color data that are set to carry value corresponding to either
the foreground or background color that have been specified for use in this conversion process. If a given
bit of monochrome source data carries a value of 1, then the byte(s) of color data resulting from the
conversion process will be set to carry the value of the foreground color. If a given bit of monochrome
source data carries a value of 0, then the resulting byte(s) will be set to the value of the background color.
The foreground and background colors used in the color expansion of monochrome source data can be set
in the Pattern/Source Expansion Foreground Color Register (BR02) and the Pattern/Source Expansion
Background Color Register (BR01), in which case these colors will be the same colors as those used in the
color expansion of monochrome pattern data. However, it is also possible to set the colors for the color
expansion of monochrome source data independently of those set for the color expansion of monochrome
pattern data by using the Source Expansion Foreground Color Register (BR0A) and the Source Expansion
Background Color Register (BR09). Bit 27 in the BitBLT Monochrome Source Control Register (BR03) is
used to select between one or the other of these two sets of registers.
The BitBLT engine requires that the alignment of each scan line’s worth of monochrome source data be
specified. In other words, whether each scan line’s worth of monochrome source data can be assumed to
start on quadword, doubleword, word, or byte boundaries, or that it cannot be assumed to start on any such
boundary must be specified using bits 26-24 of the Monochrome Source Control Register (BR03).
The BitBLT engine also provides various clipping options for use with monochrome source data. Bits 21-16
of the Monochrome Source Control Register (BR03) allow the BitBLT engine to be programmed to skip up
to 63 of the 64 bits in the first quadword of a block of monochrome source data to reach the first bit of valid
source data. Depending on the width of the block of pixels represented by the monochrome source data,
this option can also be used to implement a way of clipping the monochrome source data from the top. Bits
5-0 of this register allow up to 63 of the 64 bits in the first quadword in each scan line’s worth of monochrome
source data to be skipped to reach the first bit of valid source data in each scan line’s worth. This option
can be used to implement the clipping of each scan line’s worth of monochrome source data from the left.
Bits 13-8 of this register provides similar functionality for clipping monochrome source data from the right.
Pattern Data
The pattern data must exist within the frame buffer where the BitBLT engine may read it directly. The host
CPU cannot provide the pattern data to the BitBLT engine. As shown in Figure E-8, the block of pattern
graphics data always represents a block of 8x8 pixels. The bits or bytes of a block of pattern data may be
organized in the frame buffer memory in only one of four ways, depending upon its color depth which may
be 8, 16, or 24 bits per pixel (whichever matches the color depth to which the BitBLT engine has been set),
or monochrome.
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69000 Databook
Subject to Change Without Notice
Revision 1.3 8/31/98