II.5 - Command Set Overwiew
Dyd
DXd
PEN
68483-12.EPS
Figure 11
II.5.1 - LINEAR DRAWING
LINE (Xd, Yd, DXd, DYd). ARC (Xd, Yd, DXd, DYd,
RAD, STOP).
The curve may be drawn with any pen and with any
linear texture (register R3). For each set of com-
puted coordinates, R3 is right rotated and the pen
is printed when the shifted bit is set.
II.5.2 - AREA DRAWING
- RECT (Xd, Yd, DXd, DYd)
- TRAPEZIUM (Xd, Yd, DXd, DYd, X1)
- POLYGON (Xd, Yd, DXd, DYd)
- POLYARC (Xd, Yd, DXd, DYd, RAD, STOP)
Either RECT or TRAPEZIUM allows to draw directly
all the pels inside the boundary.
Any other closed boundaries may be filled by a
3-step process :
1. The mask bits inside a boundary box must be
reset by a RECT command.
2. Asequence of mixed POLYGON and POLYARC
commands describing the closed boundarysets
the mask bits of the pels inside this boundary.
3. Th i s a r e a ma y th en be p a in t e d b y a
RECTANGLE command defined for a bounding
box, with destination masking. It may also be
tiled by use of a PRINT CELL command.
Note : the mask bit of any pel lying on the boundary
itself is not guaranteed to be set by step 2.
II.5.3 - PRINT CELL COMMANDS
PRINT CELL (Xd, Yd, DXd, DYd ; Xs, Ys, DXs,
DYs).
The cell addressed by Xs, Ys, DXs, DYs is scaled
then printed at location Xd, Yd and clipped at the
dXd, dYd dimensions.
When dXd, dYd is much larger than DXs, DYs the
command may be parametered for repeat drawing.
These commands may also be parametered for
destination mask use.
Further more the PRINT OBJECT command may
be parametered for source mask use.
These commands have a wide range of applica-
tions : text drawing, area tiling, print or move ob-
jects, scale and move viewports.
Note : an underlined cell is drawn when the MSB
of R23 is set.
II.5.4 - ACCESS COMMANDS
- LOAD VIEWPORT (Xs, Ys, DXs, DYs)
- SAVE VIEWPORT (Xs, Ys, DXs, DYs)
- MODIFY VIEWPORT (Xs, Ys, DXs, DYs)
These commands provide sequential access to a
viewport in a frame buffer from the microprocessor
data base.
Data are transferred to/from the display memory,
word sequentially.
The R14 to R17 registers are used as a two mem-
ory word FIFO (memory word is 8 short pels, i.e. 4
bytes).
The source pointer (R20-R23) is used to address
the viewport for all access commands.
When long pels are used, the command must be
executed once more when the bank number in R20
has been updated.
II.5.5 - COMMAND EXECUTION
Each on-chip 16-bit register has four addresses.
One address is used for plain read or write. The
other addresses are used to initiate command exe-
cution automatically on completion of the register
access.
This scheme allows the command code and its
arguments to be loaded or modified in any other.
An incremental line drawing command, for exam-
ple, may be executed again and again with succes-
sive incremental dimensions and whithout need to
reload the command code itself.
As soon as a command execution is started, the
FREE bit is cleared in the STATUS register. This bit
is automatically set when the execution is com-
pleted.
The commands are generally executed only during
retrace intervals. However full time execution is
possible when either the display is disabled or
video RAM components are used.
II.5.6 - STATUS REGISTER (see Figure 12)
This register holds four read-only status bits :
- FREE : this status bit is set when no execution is
pending
- VS : vertical synchronization state
- SEM : this status bit is set when the FIFO memory
word is inacessible to the microprocessor during
a viewport transfer
- NSEM : this status bit is set when the FIFO
memory word is accessible to the microprocessor
during a viewport transfer.
Each of these status bits is maskable. The masked
status bits are NORed to the IRQ output pin.
TS68483A
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