M69000 Asiliant Technologies, M69000 Datasheet - Page 338

• Manufacturer Part Number: M69000
• Manufacturer: Asiliant Technologies

Specifications of M69000

• Lead Free Status / Rohs Status: Supplier Unconfirmed

BitBLT Operation
E-3
Graphics Data Size Limitations
The BitBLT engine is capable of transferring very large quantities of graphics data. Any graphics data read
from and written to the destination is permitted to represent a number of pixels that occupies up to 8191
scanlines and up to 8191 bytes per scanline at the destination. Therefore, the maximum number of pixels
that may be represented per scanline’s worth of graphics data depends on the color depth.
Any source data must represent both the same number of pixels per scanline and the same number of
scanlines as both the input and output destination data. Despite these constraints, if the source data is
received from the host CPU via the BitBLT dataport, that source data may be received as part of a much
larger block of data sent by the host CPU. The BitBLT engine may be programmed to skip over various
quantities of bytes within such a block in order to reach the bytes containing valid source data.
The actual number of scanlines and bytes per scan line required to accommodate both input and output
destination data are set in BR08. These two values are essential in the programming of the BitBLT engine,
because these values are used by the BitBLT engine to determine when a given BitBLT operation has been
completed. It is important to note that writing a non-zero value to BR08 is the trigger that causes the BitBLT
engine to begin a BitBLT operation. Therefore, all other registers must be set as desired for a given BitBLT
operation before BR08.
Bit-Wise Operations
The BitBLT engine can perform any one of 256 possible bit-wise operations using various combinations of
the source, pattern, and input destination data as inputs. These 256 possible bit-wise operations are
designed to be compatible with the manner in which raster operations are specified in the BitBLT parameter
®
block used in the Microsoft
Windows
environment, without translation.
The choice of bit-wise operation selects which of the three inputs will be used, as well as the particular
logical operation to be performed on corresponding bits from each of the selected inputs. The BitBLT
engine will automatically forego reading any form of graphics data that has not been specified as an input
by the choice of bit-wise operation. An 8-bit code written to BR04 chooses the bit-wise operation. The
tables on the following pages list the available bit-wise operations and their corresponding 8-bit codes.
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69000 Databook
Subject to Change Without Notice
Revision 1.3 8/31/98