MOTOROLA
MC68322 USER’S MANUAL
11-1
SECTION 11
RISC GRAPHICS PROCESSOR
The RISC graphics processor (RGP) is one of the two components of the graphics unit; the
other being the print engine interface. The RGP executes a display list of graphic orders (a
special list of instructions) to render a page image. This section describes the following RGP
functional blocks and how they operate.
Graphic order parser
Graphic order execution unit
Band registers
Arithmetic logic unit
Pixel data files
Boolean logic unit
The graphic order parser is responsible for reading the display list and determining opcode
type and, if a banded opcode, the appropriate band to process the graphic order. It is also
responsible for aligning and transferring the operands into the band registers, interpreting,
aligning, and transferring scanline table bit string specifiers into the band registers, as well
as writing back any modified operands in the event of a band fault.
The graphic order execution unit is a collection of state machines that control all aspects of
the graphic operations, including calculation of effective addresses, rectangular pixel array
widths in words, barrel shifter rotation offsets, left/right mask values, and halftone
positioning. The band registers hold the graphic order operands and values that are required
for internal use. The arithmetic logic unit performs all internal calculations including addition,
subtraction, increment by one, decrement by one, and comparison. It is also used to
calculate and modify effective addresses for source, destination, and halftone bit maps.
The pixel data files (along with internal barrel shifters) hold source, halftone, and destination
data, and it constantly adjusts so that all the data is uniformly aligned. These data files
operate independently from the remainder of the RGP, requesting new data at the same
time existing data is processed through the barrel shifters or Boolean logic unit for
subsequent writing to memory.
The Boolean logic unit carries out all combinations of 1-, 2-, and 3-operand Boolean
operations, combining source, halftone, and destination data together in one of 256 possible
combinations. Left and right masking is used to preserve the original destination data at the
left and right edges of the destination bitmap.
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