Graphic Operations
12-8
MC68322 USER’S MANUAL
MOTOROLA
A 16-bit null termination bit string specifier of 0000
16 is placed before the beginning and after
the end of every scanline table. This is a real specifier that specifies no movement of the
base pointer and a run of zero pixels. Note that the null terminators can be shared between
scanline tables placed adjacent in memory. In other words, the ending point 0000
16 of one
scanline table serves as the starting point 0000
16 for the next scanline table. The dual
termination of the scanline tables is required for duplex banding applications where the
MC68322 reads the scanline table in both forward and reverse directions to render 0
° and
180
° pages.
12.6.2 Scanline Run Operation
When a scanline graphic order begins, the current destination address is established by the
initial address specified in the graphic order. The MC68322 maintains a current destination
address value and updates it after each bit string specifier is executed. For 0
° pages, after
a scanline run occurs, the current destination address points to the pixel immediately
following the last pixel in the run. For 180
° pages, the current destination address points
where the last specifier’s X and Y displacements put it.
The displacements specified by DX, DY (for 16- and 32-bit bit string specifiers), and DZ (for
48-bit bit string specifiers) are applied before executing the scanline run for a 0
° page and
after executing it for a 180
° page. Figure 12-4 illustrates a scanline run using the values in
the bit string specifier fields. Notice that destination address A is the initial address for 0
°
pages as well as the final address for 180
° pages and, in turn, address B is the final address
for 0
° pages and the initial address for 180° pages.
Figure 12-4. Scanline Run Operation
Table 12-2. Bit String Specifier Field Definitions
BIT STRING TYPE
FIELD
DEFINITION
16-bit
DY
Zero to one scanline.
RL
0 to 63 pixels.
DX
+127 to –128 pixels.
32-bit
DY
Zero to three scanlines.
RL
0 to 4,095 pixels.
DX
+8,191 to –8,192 pixels.
48-bit
RL
0 to 16,383 pixels.
DZ
+536,870,991 to –536,870,992 pixels.
DY
DX
RL
DESTINATION
ADDRESS A
DISPLACEMENT
DESTINATION
ADDRESS B
SCANLINE RUN
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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