Atari 800 User Manual

88 User's Handbook to the Atari 400/ 800 Computers
will return the row and column numbers respectively.
When PRINT is used to output data to the screen, the previous
cu rsor position
is stored in memory . Memory add ress 90
contains the last row number, and memory address 91 contains
the last column number. Again, the PEEK function can be used to
examine the contents of these memory addresses.
Remember, rows are
numbered from 0 to 23, and columns are
numbered from 0 to 39.
Changing the Display Screen Margins
The standard left margin on the display screen is column 2. The
standard right margin
is column 39. The Atari uses memory
address 82 to store the column number of the left margin, and
location 83 to store the column number of the right margin.
The
POKE statement can be used to change either the left or
right margins. The following statements would reset the left
margin to column 5, and the right margin to column 30.
POKE 82 , 5
POKE 83 , 30
Screen Input Programming
Input programming is a vital part of BASIC programming. Nearly
every BASIC program requires some form of operator input. In
the following few sections, we will discuss programming
practices that are designed to make operator input efficient and
as error-free as possible.
Prompt Messages
One programming principle that should nearly always be
followed in input programming is to include a prompt message
with the INPUT statement. An example is given below .
100 PRINT "ENTER YOUR AGE";
200 INPUT AGE

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