Atari 800 Basic Reference Manual

PLOT (PL.)
Doing a PRINT after a LOCATE or GET from the screen may cause the data in
the pixel which was examined to be modified. This problem is avoided by
repositioning the cursor and putting the data that was read, back into the pixel
before doing the PRINT. The following program illustrates the use of the
LOCATE command.
10 GF.:AF'H I C::; 3+ 16
;2€1 COLOP 1
30 ::;ETCOLOF.: 2 .. 1 ~3, :3
40 PLOT 1~3 .. 15
5€1 DPAl·nO 15 _, 15
6ft LOCATE 12 .. 15_, i<
70 F'RH-H ;:.::
Figure 9-2. Example Program Using LOCATE
On execution, the program prints the data (1) determined by the COLOR state-
ment which was stored in pixel 12, 15.
Format:
Example:
PLOT aexp1, aexp2
100 PLOT 5,5
The PLOT command is used in graphics modes 3 through 8 to display a point in
the graphics window. The aexp1 specifies the X-coordinate and the aexp2 the
Y-coordinate. The color of the plotted point is determined by the hue and
luminance in the color register from the last COLOR statement executed. To
change this color register, and the color of the plotted point, use SET-
COLOR.
Points that can be plotted on the screen are dependent on the graphics
mode being used. The range of points begins at 1 and extends to one less than
the total number of rows (X-coordinate) or columns (Y-coordinate) shown in
Table 9-1.
POSITION (POS.) Format:
POSITION aexp1, aexp2
100 POSITION 8, 12
PUT/GET
(PU./GE.)
Example:
The POSITION statement is used to place the invisible graphics window cursor
at a specified location on the screen (usually precedes a PRINT statement). This
statement can be used in all modes. Note that the cursor does not actually move
until an I/0 command which involves the screen is issued.
Formats: PUT #aexp, aexp
GET #aexp, avar
Examples: 100 PUT #6, ASC(" A")
200 GET #1, X
In graphics work, PUT is used to output data to the screen display. This state-
ment works hand-in-hand with the POSITION statement. After a PUT (or GET),
the cursor is moved to the next location on the screen . Doing a PUT to device #6
causes the one-byte input (second aexp) to be displayed at the cursor position.
The byte is either an AT ASCII code byte for a particular character (modes 0-2) or
the color data (modes 3-8).
GET is
used to input the code byte of the character displayed at the cursor posi-
tion, into the specified arithmetic variable. The values used in PUT and GET cor-
respond to the values in the COLOR statement. (PRINT and INPUT may also be
used.)
Graphic Modes and Commands 49

Atari 800 Specifications

General

Processor	MOS Technology 6502
Processor Speed	1.79 MHz
ROM	10 KB
Graphics	ANTIC and GTIA chips
Release Year	1979
Display Resolution	up to 320 x 192
Colors	128 colors
Sound	4 channels
Storage	Cartridge, cassette, floppy disk
Ports	Cartridge, serial, monitor
Operating System	Atari OS