NS32CG16-10 Datasheet, PDF (20/82 Pages) National Semiconductor (TI) – High-Performance Printer / Display Processor

2 0 Architectural Description (Continued)
curs any time the screen is moved in a purely vertical direc-
tion as in scrolling text It should be noted that in both of
these cases the choice of horizontal BITBLT direction may
be made arbitrarily
Figure 2-10(b) demonstrates a case in which the horizontal
BITBLT direction may not be chosen arbitrarily This is an
instance of purely horizontal movement of data (panning)
Because the movement from source to destination involves
data within the same scan line the incorrect direction of
movement will overwrite data which will be needed later In
this example the correct direction is from right to left
2 5 2 5 BITBLT Variations
The ‘‘classical’’ definition of BITBLT as described in
‘‘Smalltalk-80 The Language and its Implementation’’ by
Adele Goldberg and David Robson provides for three oper-
ands source destination and mask texture This third oper-
and is commonly used in monochrome systems to incorpo-
rate a stipple pattern into an area These stipple patterns
provide the appearance of multiple shades of gray in single-
bit-per-pixel systems in a manner similar to the ‘‘halftone’’
process used in printing
x Texture op1 Source op2 Destination Destination
While the NS32CG16 and the external BPU (if used) are
essentially two-operand devices three-operand BITBLT op-
erations can be implemented quite flexibly and efficiently by
performing the two operations serially
2 5 3 GRAPHICS SUPPORT INSTRUCTIONS
The NS32CG16 provides eleven instructions for supporting
graphics oriented applications These instructions are divid-
ed into three groups according to the operations they per-
form General descriptions for each of them and the related
formats are provided in the following sections
2 5 3 1 BITBLT (BIT-aligned BLock Transfer)
This group includes seven instructions They are used to
move characters and objects into the frame buffer which will
be printed or displayed One of the instructions works in
conjunction with an external BITBLT Processing Unit (BPU)
to maximize performance The other six are executed by the
NS32CG16
BIT-aligned BLock Transfer
Syntax BB(function) Options
Setup
R0
R1
R2
R3
R4
R5
R6
R7
0(SP)
base address source data
base address destination data
shift value
height (in lines)
first mask
second mask
source warp (adjusted)
destination warp (adjusted)
width (in words)
Function AND OR XOR FOR STOD
Options IA
Increasing Address (default option)
When IA is selected scan lines are
transferred in the increasing BIT BYTE
order
DA Decreasing Address
S
True Source (default option)
bS Inverted Source
These five instructions perform standard BITBLT operations
between source and destination blocks The operations
available include the following
BBAND
BBOR
BBXOR
BBFOR
BBSTOD
src AND dst
bsrc AND dst
src OR dst
bsrc OR dst
src XOR dst
bsrc XOR dst
src OR dst
src TO dst
bsrc TO dst
‘src’ and ‘bsrc’ stand for ‘True Source’ and ‘Inverted
Source’ respectively ‘dst’ stands for ‘Destination’
Note 1 For speed reasons the BB instructions require the masks to be
specified with respect to the source block In Figure 2-9 masking
was defined relative to the destination block
Note 2 The options bS and DA are not available for the BBFOR instruc-
tion
Note 3 BBFOR performs the same operation as BBOR with IA and S op-
tions
Note 4 IA and DA are mutually exclusive and so are S and bS
Note 5 The width is defined as the number of words of source data to read
Note 6 An odd number of bytes can be specified for the source warp
However word alignment of source scan lines will result in faster
execution
The horizontal and vertical directions of the BITBLT opera-
tions performed by the above instructions with the excep-
tion of BBFOR are both programmable The horizontal di-
rection is controlled by the IA and DA options The vertical
direction is controlled by the sign of the source and destina-
tion warps Figure 2-11 and Table 2-3 show the format of
the BB instructions and the encodings for the ‘op’ and ‘i’
fields
23
16 15
87
0
0 0 0 0 0 0 D X S 0 op i 0 0 0 0 1 1 1 0
 D is set when the DA option is selected
 S is set when the bS option is selected
 X is set for BBAND and it is clear for all other BB instructions
FIGURE 2-11 BB Instructions Format
TABLE 2-3 ‘op’ and ‘i’ Field Encodings
Instruction Options ‘op’ Field ‘i’ Field
BBAND
Yes
1010
11
BBOR
Yes
0110
01
BBXOR
Yes
1110
01
BBFOR
No
1100
01
BBSTOD
Yes
0100
01
BIT-aligned Word Transfer
Syntax BITWT
Setup
R0 Base address source word
R1 Base address destination double word
R2 Shift value
The BITWT instruction performs a fast logical OR operation
between a source word and a destination double word
stores the result into the destination double word and incre-
ments registers R0 and R1 by two Before performing the
OR operation the source word is shifted left (i e in the
direction of increasing bit numbers) by the value in register
R2
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