Graphic Orders
MOTOROLA
MC68322 USER’S MANUAL
13-7
Figure 13-2. Halftone Specification for bitBLT Operations
13.4 BAND NUMBER AND BAND FAULTS
Each of the MC68322 graphic orders that operate on a banded bitmap contains a band
number parameter. The band number is used by the MC68322 to determine when to
execute the graphic order. Graphic orders whose band numbers match the current band
being rendered are executed. Otherwise, the graphic order is skipped. Band numbers
always increase in value from the top band to the bottom band of the image, regardless of
the type of page (0
° or 180°) being rendered. The band number for a graphic order must be
determined by the software. It must be the number of the band where the first scanline of a
graphic order resides when rendering a 0
° page or the number of the band where the last
scanline of a graphics order resides when rendering a 180
° page.
In banding applications, bitBLT and scanline operations can extend beyond the bottom (or
top, for 180
° pages) boundary of a band. The MC68322 detects such band crossings (or
band faults) during the course of the bitBLT or scanline operation. When a band fault occurs,
the operation is prematurely terminated and the MC68322 accesses the display list to
update the graphic order’s parameters, including its band number, bitmap and scanline table
addresses, and frame bitmap heights. The graphic order parameters are written back into
the display list to begin the operation following the point of the band fault at the top (or bottom
for 180
° pages) of the next band. The MC68322 automatically adjusts the band number
when the graphic order spans multiple bands. When a band fault occurs, the band number
is incremented or decremented depending on the setting of the B2T flag. If the B2T flag is
clear, the band number is incremented when an operation crosses a band boundary. If the
B2T flag is set, the band number is decremented.
HXR
HALFTONE BITMAP,
SHOWN TILED
SOURCE
FRAME
HA
HYR
0
° PAGE
TOP TO BOTTOM
HALFTONE BITMAP,
SHOWN TILED
SOURCE
FRAME
180
° PAGE
TOP TO BOTTOM
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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