Atari 400 User manual

ERROR CODES
ERROR
CODE ERROR CODE MESSAGE
2
Memory In s ufficient
3
Va lue Error
4 Too
Many Vari ab l es
5
String Length Error
6
Out of Data Error
7
Number greater than 32767
8
Input Statement Error
9
Array or String DIM Error
10 Argument Stack Overflow
11 Fl oating Point Overflow /
Underflow Error
12
Line Not Found
13
No Matching FOR S ta tement
14
Line Too Long Error
15
GOSUB or FOR Lin e Del eted
16
RE TUR N Error
17
Garbage Error
18
In va lid String Character
Note : Th e foll owing are INPUT / OUTPU T er-
rors that resu lt du r in g th e u se of disk dri ves,
pr i nt e rs , or ot h er accessory d ev i ces . Furth er in-
fo
rm at ion is pro v id ed with th e auxilia ry hard -
ware .
19
LOAD program T oo Long
20
D ev ice Number Larger
21 L OAD File Error
128
BREAK Abort
129
IOCB
130
Nonexistent Device
131
IOCB Write Only
132 In va lid Comm a nd
133
D ev ic e or File not Op en
134
BAD IO CB ~umb er
135
IO CB R ea d On ly Error
136
EOF
137 Truncat ed R eco rd
138
De vice Tim eo ut
139
D evice NAK
140
Seri al Bus
141
C ursor Out of Ra ng e
ERROR
CODE ERROR CODE MESSAGE
142 Ser ial Bus Data Frame O verr un
143 Serial bus data fr ame checks um er ror
144 Dev i cP rlone e rr or
145 Read af t er write compare error
146 Funct ion not implemen ted
147 In sufficient RAM
160 Drive numb er er ror
161 Too many OPEN files
162 Disk full
163 U nrecov e rab le system data I/ 0 er ror
164 File number mi smatch
165 File name error
166 POINT d ata le ngth error
167 File l ocked
168 Command inva lid
169 Director y full
170 File not found
171 POINT i nvalid
For ex pl ana tion of Err or Mes sages see Appendix B.

TABLE OF MODES
AND SCREEN FORMATS
Vert. (Rows)
Vert. (Rows)
RAM
Gr.
Mode
Horiz.
Split
Full
II Of
Requir ed
Mod e Ty pe
(Column s)
Scre en
Screen
Colors
(B y t es )
0 TE
XT 40 -24 2
993
1
TEXT 20
20 24
5
513
2 TEXT
20
10
12 5
26 1
3 GRAPHI
CS 40 20
24 4 2
73
4 GR
AP HI CS 80
40
48 2
537
5 GRA PHI
CS
80
40 48
4 1
017
6
GR APHI CS 160
80 96 2
2025
7 GR APHI CS 160 80
96
4
3945
8
GRAPH ICS
320
1 60
1 92
1/2
7900
MODE, SET COLOR, COLOR TABLE
SETC OLOR
(a ex pl)
De fault
Mod e or C olor
C olo r
C
ol ors
Co nditi on Re
gi ster No.
(aex p)
DESCRIP TIO N AN D C OM MENTS
0 COLOR da ta -
LIGHT BLUE MODE 0 a nd
1 ac tu ally Cha
ra cter lum in ance ( sa m e color as bac kground )
DARK BLUE ALL
TEXT
2 de te rmines Back gro un d
WINDOWS
3 ch
arac t er to -
BLACK 4
be pl ot ted Borde1·
ORANGE
0 COLOR data
Cha1·acter
LI
GHT GREEN MODES 1 1
actually determine s Ch aracte r
DARK BLUE a
nd
2 cha
ra cter to be Ch aracter
RED 2 3 plott
ed
Char acte r
BL ACK (
Text Modes) 4
Backgro und , Bord er
ORANGE 0 1
Gr ap hics poin t
LIGHT GREEN MODES
3, 5, 1 2
Gra p hi cs poin t
DARK BLUE
and 7 2 3 Graph ics poi nt
(Four - co l or
3 -
BLACK
Mode s) 4 0 Gra
phics point (bac kgr ou nd defa ult ), Bo rder
ORANGE MODES 4 0 1
Grap hics point
an d 6 1 -
(Two- co lor 2 -
Mo de s) 3 -
BLACK 4 0 Gr
ap hi cs point ( bac k ground d efau lt ), Bor der
LIG HT GREEN 0 - -
DARK BLUE 1 1
Grap hi cs p oin t lumi nan ce (sa me col or as b ackgr ou nd)
MODE 8 2 0 Gr ap hi cs poi nt (ba ckgr o un d deliiUlt)
(1 Col or 3 -
BLACK 2 L um in ances)
4 Bor
der

CONTENTS
PREFACE vii
1 GENERAL INFORMATION
Terminolog y 1
Sp ec ial Not a tions U se d In Thi s Manual 3
Abbre v iation s Used In This M anual
4
Operating Modes
5
Spec ial Fun c tion K eys 5
Arithmetic Operator s 6
Operator Precedence
7
Built-In Fun c tions
7
Graphics 8
Sound and Games 8
W ra pa round and Key board Rollover 8
Error Messages 8
2 COMMANDS
BYE
9
CONT
9
E ND
9
LET 10
LIST
10
NEW
10
REM 10
RUN 11
S TOP
11
3 EDIT FEATURES
Scr ee n E diting
13
Control (CTRL) Key
13
Shift Key 13
Doub le K ey F un c ti ons
14
Cursor Control Keys
14
K ey s Used W ith CTRL Key
14
Keys Used W ith Shi ft K ey
14
Special Function Key s
14
Br e ak Ke y
14
Escape Key
14
4 PROGRAM STATEMENTS
FOR/NE XT /S TE P
15
GOSUBIRETURN
16
GOTO
17
I F/T H EN
18
Contents iii

ON/GOSUB
20
ON!GOTO
20
POP
20
RESTORE
21
TRAP
22
5 INPUT/OUTPUT COMMANDS
Input/Output Devices
23
CLOAD
24
CSAVE 24
DOS 25
ENTER
25
INPUT
25
LOAD
26
LPRINT
26
NOTE
26
OPEN/CLOSE
26
POINT
28
PRINT
28
PUT/GET 28
READ/DATA
28
SAVE
29
STATUS
29
XIO
30
Chaining Programs
30
6 FUNCTION LIBRARY
Arithmetic Functions
33
ABS
33
CLOG
33
EXP
33
INT
33
LOG
34
RND
34
SGN 34
SQR 34
Trigonometric Functions
34
ATN
34
cos
34
SIN
35
DEG/RAD
35
Special Purpose Functions
35
ADR
35
FRE
35
PEEK
35
POKE
35
USR
36
7 STRINGS
ASC
37
CHR$
37
iv
Contents

LEN
38
STR$
38
VAL
38
Str ing Ma nipul a tion s
39
8
ARRAYS AND MATRICES
DIM
41
CLR
43
9
GRAPHICS MODES AND COMMANDS
GRAPHICS
45
Graphics Modes
45
ModeO
46
Mo de s 1 and 2 46
Mod es 3, 5, and 7 47
Mod es 4 a nd 6
48
Mode8
47
COLOR
48
DRA W TO 48
LOCATE 48
PLOT 49
POSITION 49
PUT/GET
49
SETCOLOR
50
XIO ( Sp e cial Fill Application) 54
A ss igning Colors to Tex t Modes
54
Gra ph ic s Co nt r ol C har acter s 56
10
SOUND AND GAME CONTROLLERS
SOUND
57
PADDLE
59
PTRIG
59
ST ICK
59
STRIG
60
11 ADVANCED PROGRAMMING TECHNIQUES
Mem ory Con servat ion
61
Programm i ng In M ac hin e La ngu age
63
APPENDIX A
BASIC RESERVED WORDS
A-1
APPENDIX B
ERROR MESSAGES
B-1
APPENDIX C
ATASCII CHARACTER SET
WITH DECIMAL /
HEXADECIMAL LOCATIONS
C-1
APPENDIX D
ATARI 400 / 800
MEMORY MAP
D-1
Conte nts V

APPENDIX E DERIVED FUNCTIONS
E-1
APPENDIX F
PRINTED VERSIONS OF
CONTROL CHARACTERS F-1
APPENDIX G GLOSSARY G-1
APPENDIX H USER PROGRAMS
H-1
APPENDIX I MEMORY LOCATIONS 1-1
INDEX
117
vi Conte nt s

PREFACE
This manual assumes the user has read the Atari BASIC -A Self-Teaching
Guide or some other book on BASIC. This manual is not intended to "teach"
BASIC. It is a reference guide to the commands, statements, functions, and
special applications of Atari® BASIC.
The programs and partial programming examples used in this manual are
photostats oflistings printed on the Atari 820™ Printer. Some of the special sym-
bols in the Atari character set do not appear the same on the printer; e.g., the
clear screen symbol '~" appears as a " } ". The examples in the text were
chosen to illustrate a particular function- not necessarily "good" programming
techniques.
Each of the sections contains groups of commands, functions, or statements
dealing with a particular aspect of Atari BASIC. For instance, Section 9 contains
all the statements pertaining to Atari's unique graphics capabilities. The appen-
dices include quick references to terms, error messages, BASIC keywords,
memory locations, and the AT ASCII character set.
As there is no one specified application for the Atari Personal Computer System,
this manual is directed at general applications and the general user. Appendix H
contains programs that illustrate a few of the Atari system's capabilities.
Preface vii

TERMINOLOGY
1
GENERAL
INFORMATION
This section explains BASIC terminology, special notations , and abbre v iation s
used in this manual, and the special keys on the AT ARI 400™ and AT ARI 800 ™
Personal Computer Systems keyboard . It also points to other sections where
BASIC commands deal with specific applications.
BASIC: Beginner's All-purpose Symbolic Instruction Code.
BASIC Keyword: Any reser v ed word "legal " in the BASIC language. May be
used in a statement , as a command, or for any other purpose. (See Appendi x A
for a list of all "reserved words" or keywords in AT ARI BASIC.)
BASIC Statement: Usually begins with a keyword , like LET, PRINT, or
RUN.
Constant: A constant is a value expressed as a number rather than represented
by a variable name . For example, in the statement X = 100 , X is a v ariable and
100 is a constant. (See Variable.)
Command String: Multipl e commands (or pr o gr am st at em e nt s) pl ac ed on th e
same numbered line separated by colons.
Expression: An e xpression is i my le gal c ombin a tion of va riables , c onstan ts,
operators, and functions used together to compute a value. Expressions can be
either arithmetic, logical, or string .
Function: A function is a computation built into the computer so that it can be
called for by the user 's program. A function is NOT a statement ; it is part of an
expressi o n. It is r ea lly a subroutin e used to c omput e a va lu e which is then
"returned" to the main program when the subroutine returns. COS (Cosine),
RND (random), FRE (unused memory space), and INT (integer ) are ex amples of
functions . In man y cases th e v alue is s impl y as sign ed to a va riabl e (stored in a
var iable) for lat er use. In other ca s es it may be print ed out on th e scr een im-
mediately. See Section 6 for more on functions. Examples of functions as they
might appear in programs are:
10 PF.:HH F.l[l( 0)
( print ou t the random
numb er ret urn ed)
(add
the value re-
r et urn ed to 100 a nd
sto re the to ta l in
variable
X)
General In fo r ma tion 1

2 Gene ral Inf orm at ion
Logical Line: A logical line consists of one to three physical lines, and is ter-
minated either by a l;i#iii;lli or automatically when the maximum logical line
limit is reached. Each numbered line in a BASIC program consists of one logical
line when displayed on the screen. When entering a line which is longer than
one physical line, the cursor will automatically go to the beginning of the next
physical line when the end of the current physical line is reached . Ifi@ii!;lllis
not entered, then both physical lines will be part of the same logical line.
Operator: Operators are used in expressions. Operators include addition (+),
subtraction (- ), multiplication ( * ), division (/), exponentiatinn (A), greater than
(>), less than (<),equal to (= ) ,greater than or equalt o(>=), less than or equalto
( <,::: ), and not equal to (< > ). The logical keywords AND, NOT and OR are also
operators. The + and - operators can also be used as unary operators; e. g., -3.
Do not put several unary operators in a row; e.g.,--3 , as the computer will in-
terpret it incorrectly.
Physical Line: One line of characters as displayed on a television screen.
String: A string is a group of characters enclosed in quotation marks.
"ABRACADABRA" is a string. So are " ATARI MAKES GREAT COMPUTERS"
and "123456789" . A string is much like a constant, as it too, may be stored in a
variable . A string v ariable is different, in that its name must end in the
character$. For example, the string "AT ARI 800" ma y be assigned to a variable
called A$ using (optional) LET like this:
10 LET A$="ATAF.J 8H0"
OR (note quot
ation marks)
(LET is optional; the
quotes are required.)
Quotation marks may n ot be used within a string. However , the closing quota-
tion can be omitted if it is the last character on a logical line. (See Section 7 -
STRINGS).
Variable: A variable is the name for a numerical or other quantity which may
(or may not) change. Variable name s ma y be up to 120 characters long.
However, a variable name must start with an alphabetic letter, and ma y contain
only capital letters and numerical digits. It is ad v isable not to use a ke yw o rd as a
variable name or as the first part of a va riable name as it m ay not be inte r preted
correctly. Examples of s toring a value in a vari a ble:
LETC 123Dt..J8= 1. 234
LETI . .JARIABLE112=267 . 543
LETA=1
LET F5TH=6 .5
LET TH J::;HO = 59 . :: : £19
Note: LET is optional and may be omitted)
Variable Name Limit: ATARI BASIC limits the user to 128 variable names .To
bypass this problem , use individual elements of an arra y instead of having
separate vari a ble names. BASIC keeps all refe r ence s to a variabl e which has
been deleted from a program , and the name still remains in the variable name
table.

SPECIAL
NOTATIONS
USED IN THIS
MANUAL
Ifthe screen displays an ERROR-4 (Too Many Variables) message, use the follow -
ing procedure to make room for new variable names:
LIST f i 1 eSPec
I'£~J
ENTER f i 1 esPec
The LIST filespec writes the untokenized version of the program onto a disk or
cassette. NEW clears the program and the table areas. The program is then re-
entered, re-tokenized, and a new variable table is built . (The tokenized version
is Atari BASIC's internal format. The untokenized versions in ATASCII
which is the version displayed on the screen).
Arrays and Array Variables: An array is a list of places where data can be
filed for future use. Each of these places is called an element, and the whole array
or any element is an array variable. For example, define "Array A" as having 6
elements. These elements are referred to by the use of subscripted va riables
such as A(2), A(3), A(4), etc. A number can be stored in each element. This
may be accomplished element by element (using the LET statement), or as a part
of a FOR/NEXT loop (see Chapter 8).
Note: Never leave blanks between the element number in parentheses and the
name ofthe array.
Correct
A(23)
ARRAY(3)
X123(38)
Incorrect
A
ARRAY
X123
(23)
(3)
(38)
Line Format: The format of a line in a BASIC program includes a line number
(abbreviated to lineno) at the beginning of the line , followed by a statement
keyword, followed by the body of the statement and ending with a line ter-
minator command (Wi!li13key). In an actual program, the four elements might
look like this:
Line Number
100
STATEMENT
Keyword
PRINT
Body
A/X * (Z + 4 . 567)
Terminator
l;ljilt;t:•
Several statements can be typed on the same line provided they are separated by
co lons (:). See IF/THEN in Section 5, and Section 11.
Capital Letters: In this book, denote keywords to be typed by the user in up-
per case form exactl y as the y are printed in this text. Reverse-video characters
will not work except in the case of the RUN command. Here are a few ex-
amples:
PRINT INPUT LIST END GOTO
GO S UB FOR NEXT
IF
Lower Case Letters: In this manual, lower case letters are used to denote the
various classes of items which may be used in a program, suc h as variables
(var) , expressions (exp), and the like . The abbreviations used for these classes of
items are shown in Table 1.1.
General Information 3

ABBREVIATIONS
USED IN THIS
MANUAL
4 General Information
Items in Brackets: Brackets, [ ], contain optional items which may be used ,
but are not required. If the item enclosed in brackets is followed by three dots
[exp, .. .], it means that any number of expressions may be entered, but none are
required.
Items stacked vertically in braces: Items stacked vertically in braces indicate
that any one ofthe stacked items may be used, but that only one at a time is per-
missible. In the example below, type either the GOTO or the GOSUB.
{
GOTO}
100 GOSUB 2000
Command abbreviations in headings: If a command or statement has an ab-
breviation associated with it, the abbreviation is placed following the full name
of the command in the heading; e.g., LET (L.).
The following table explains the abbre v iations used throughout th is manual:
avar
svar
mvar
var
aop
lop
aexp
lexp
TABLE 1.1 ABBREVIATIONS
Arithmetic Variable: A location where a numeric value is
stored. Variable names may be from 1 to 120 alphanumeric
characters, but must start with an alphabetic character, and all
alpha characters must be unre v ersed and upper case.
String Variable: A location where a string of characters may be
stored. The same name rules as avar apply, except that the last
character in the variable name must be a$ . String variables may
be subscripted. See Section 7, STRINGS.
Matrix Variable: Also called a Subscripted Variable. An ele-
ment of an array or matrix. The variable name for the array or
matrix as a whole may be any legal v ariable name such as A, X,
Y, ZIP, or K. The subscripted variable (name for the particular
element) starts with the matrix v ariable, and then use s a number,
variable, or expression in parentheses immediately following the
array or matrix variable. For example, A(ROW), A(1), A(X + 1).
Variable: Any variable. May be mvar, avar, or svar .
Arithmetic operator.
Logical operator.
Arithmetic Expression: Generally composed of a variable ,
function, constant, or two arithmetic expressions separated by an
arithmetic operator .
Logical Expression: Generall y composed of two arithmetic or
string express i ons separated by a logical operator. Such an ex-
pression evaluates to either a 1 (logical true) or a 0 (logical false).
For example, the expression 1< 2 ev aluates to the value 1 (true)
while the expression "LEMON" = "ORANGE" evalua t es to a zero
(false) as the two strings are not equal.

OPERATING
MODES
SPECIAL
FUNCTION
KEYS
sexp
exp
lineno
a data
filespec
String Expression: Can consist of a string variable, string literal
(constant), or a function that returns a string value.
Any expression, whether sexp or aexp.
Line Number: A constant that identifies a particular program
line in a deferred mode BASIC program. Must be any integer
from 0 through 32767. Line numbering determines the order of
program execution.
ATASCII Data: Any AT ASCII character excluding commas and
carriage returns. (See Appendix C.)
File Specification: A string expression that refers to a device
such as the keyboard or to a disk file. It contains information on
the type of I/0 device, its number, a colon, an optional file name,
and an optional filename extender. (See OPEN, Section 5. )
Example filespec: "D1:NATALIE.ED"
Direct Mode: Uses no line numbers and executes instruction immediately after
i;IJiiJ;I:I key is pressed.
Deferred Mode: Uses line numbers and delays execution ofinstruction(s) until
the RUN command is entered .
Execute Mode: Sometimes called Run mode . After RUN command is entered ,
each program line is processed and executed.
Memo Pad Mode: A non-programmable mode that allows the user to experi-
ment with the keyboard or to leave messages on the screen. Nothing written
while in Memo Pad mode affects the RAM-resident program.
II
Reverse (Inverse) Video key, or "ATARI LOGO KEY". Press-
ing this key causes the text to be reversed on the screen (dark
text on light background). Press key a second time to return to
normal text.
MOJ.Iitillo!ZJ;I Lower Case key: Pressing this key shif ts the screen characters
from upper case (capitals) to lower case. To restore the char a cters
to upper case, press the Ki@M key and the MOfW!l!l£.'1;1 key
simultaneously.
Escape key: Pressing this key causes a command to be entered
into a program for later execution.
Example: To clear the screen, you would enter:
10 PRINT " IB Bi3 MijUi;l "
and press 1&13.
Escape is also used in conjunction with other keys to print special
graphic control characters. See Appendix F and back cover for
the specific keys and their screen-character representations.
General Information 5

ARITHMETIC
OPERATORS
LOGICAL
OPERATORS
6 General Information
l{if31;5f.J:I
Break key: Pressing this key during program execution causes
execution to stop. Execution may be resumed by typing CONT
followed by pressing tw!lltl .
System Reset key: Similar to l!mEI in that pressing this key
stops program execution. Also returns the screen display to
Graphics mode 0, clears the screen, and returns margins and
other variables to their default values.
Tab key: Press Emm and theki!i13!;§i·i:ikeys simultaneously to
set a tab. To clear a tab, press the Gi3 and 4iiiid!;U!:I keys
simultaneously. Used alone, thekiU3!;§t.j;iadvances the cursor to
the next tab position. In Deferred mode, set and clear tabs by
preceding the above with a line number, the command PRINT, a
quotation mark, and press the Iakey.
Examples:
100 PRINT " Ia E!llil! k1U3!;$f.i:i "
200 PRINT " .. BD Ki#@d!;lt.i;i "
Default tab settings are placed at columns 7, 15, 23, 31, and 39 .
EmiiJ Insert key: Press the 1@1$4 and EmiiJ keys simultaneously to
insert a line. To insert a single character, press the Bi3 and
mm keys simultaneously.
l@§ij:f.\3¥1 Delete key: Press the «i:U:iM and ED keys simultaneously
to delete a line. To delete a single character, press Gi3 and
llE!DJ simultaneously.
Mh!J:H3¥i Back Space key: Pressing this key replaces the character to the
left of the cursor with a space and moves cursor back one space.
Emil Clear key: Pressing this key while holding down the 41:11$4 or
mill key blanks the screen and puts the cursor in the upper left
corner.
Return key: Terminator to indicate and end of a line of BASIC.
Pressing this key causes a numbered line to be interpreted and
added to a BASIC program RAM. An unnumbered line (in Direct
mode) is interpreted and executed immediately. Any variables
are placed in a variable table.
The Atari Personal Computer System uses five arithmetic operators:
+ addition (also unary plus; e.g., +5)
subtraction (also unary minus; e.g., - 5)
* multiplication
I division
A exponentiation
The logical operators consists of two types: unary and binary. The unary
operator is NOT. The binary operators are:

OPERATOR
PRECEDENCE
AND
OR
Logical AND
Logical OR
Examples:
10 IF A=12 AND T=0 THEN F'RWT "Q)00
11
Both expressions must
be true before GOOD is
printed.
10 A=(C>l) AND (N<1)
10 A = (C+l) OR Ol-1)
Hi A = NOT< C+ 1)
If both expressions
true,
A= + 1; otherwise
A=O.
If either expression
true, A= +
1; otherwise
A=O.
If expression is false,
A= + 1; otherwise A= 0.
The rest of the binary operators are relational.
< The first expression is less than the second expression.
> The first expression is greater than the second.
- The expressions are equal to each other.
< = The first expression is less than or equal to the second.
> = The first expression is greater than or equal to the second.
< >The two expressions are not equal to each other.
These operators are most frequently used in IF/THEN statements and logical
arithmetic.
Operations within the innermost set of parentheses are performed first and pro-
ceed out to the next level. When sets of parentheses are enclosed in another set,
they are said to be "nested". Operations on the same nesting level are performed
in the following order:
Highest <, >,=,<=, >=,<->
precedence
* ' I
+, -
Lowest
precedence
NOT
AND
OR
Relational operators used in string expres-
sions. Have same precedence and are per-
formed from left to right.
Unary minus
Exponentiation.
Multiplication and division have the same
precedence level and are performed from left
to right.
Addition and subtraction have the same
precedence level and are performed from left
to right.
Relational operations in numeric expressions
have the same precedence level from left to
right.
Unary operator
Logical AND
Logical OR
General Information 7

BUILT-IN
FUNCTIONS
GRAPHICS
SOUND AND
GAMES
CONTROLLERS
WRAPAROUND
AND KEYBOARD
ROLLOVER
ERROR
MESSAGES
8 General Information
The section titled FUNCTION LIBRARY explains the arithmetic and special
functions incorporated into Atari BASIC.
Atari graphics include 9 graphics modes. The commands have been designed
to allow maximum flexibility in color choice and pattern variety. Section 9 ex-
plains each command and gives examples of the many ways to use each.
The Atari Personal Computer is capable of emitting a large variety of sounds .
including simulated explosions, electronic music, and "raspberries." Section 10
defines the commands for using the SOUND function and for controlling pad-
dle, joystick, and keyboard controllers.
The ATARI Personal Computer System has screen wraparound thus allowing
greater flexibility. It also allows the user to type one key ahead. If the user
presses and holds any key, it will begin repeating after
1
h second.
If a data entry error is made, the screen display shows the line reprinted preced-
ed by the message ERROR- and the offending character is highlighted. After
correcting the character in the original line, delete the line containing the
ERROR- before pressing IDi!liJI. Appendix B contains a list of all the error
messages and their definitions.

BYE (B.)
CONT(CON.)
END
2
COMMANDS
Whenever the cursor (D) is displayed on the screen, the computer is ready to ac-
cept input. Type the command (in either Direct or Deferred mode), and press
IDiJ3. This section describes the commands used to clear computer memory
and other useful control commands:
The commands explained in this section are the following:
Format:
Example:
BYE
BYE
BYE
CONT
END
LET
LIST
NEW
REM
RUN
STOP
The current function of the BYE command is to exit BASIC and put the com-
puter in Memo Pad mode. This allows the user to experiment with the keyboard
or to leave messages on the screen without disturbing any BASIC program in
memory. To return to BASIC, press Htih&i;lihh.
Format:
Example:
CONT
CONT
Typing this command followed by a l;ijili;ill causes program execution to
resume. If a l:l;liiM, STOP, or END is encountered, the program will stop until
CONT W1!llilli is entered. Execution resumes at the next sequential line number
following the statement at which the program stopped.
Note: If the statement at which the program is halted has other commands on
the same numbered line which were not executed at the time of the l:l;q.l4'
STOP, or END, they will not be executed. On CONT, execution resumes at the
next numbered line. A loop may be incorrectly executed if.the program is
halted before the loop completes execution.
This command has no effect in a Deferred mode program.
Format: END
Example: 1000 END
This command terminates program execution and is used in Deferred mode. In
Atari BASIC, an END is not required at the end of a program. When the end of
the program is reached, Atari BASIC automatically closes all files and turns off
sounds (if any). END may also be used in Direct mode to close files and turn off
sounds.
Commands 9

LET (LE.)
LIST (L.)
NEW
REM (R. or
·'*'491)
10 Commands
Format:
Example:
[LET] var = exp
LET X = 3.142 * 16
LET X= 2
This statement is optional in defining variables. It can just as easily be left out of
the statement. It may be used, however, to set a variable name equal to a value.
Format:
Examples:
LIST [lineno [ , lineno] ]
LIST [filespec [ ,lineno [ ,lineno] ] ]
LIST
LIST
10
LIST I 101 100
LIST npn
LIST
11
0: DEt10. LST"
This command causes the computer to display the source version of all lines cur-
rently in memory if the command is entered without line number(s), or to
display a specified line or lines. For example, LIST 10,100 mi!Im displays lines
10 through 100 on the screen. If the user has not typed the lines into the com-
puter in numerical order, a LIST will automatically place them in order.
Typing L. "P will print the RAM-resident program on the printer.
LIST can be used in Deferred mode as part of an error trapping routine (See
TRAP in Section 4).
The LIST command is also used in recording programs on cassette tape. The sec-
ond format is used and a filespec is entered. (See Section 5 for more details on
peripheral devices.) If the entire program is to be listed on tape, no line numbers
need be specified.
Example: LIST "C1"
1000 LIST "C1"
Format: NEW
Example: NEW
This command erases the program stored in RAM. Therefore, before typing
NEW, either SAVE or CSAVE any programs to be recovered and used later.
NEW clears BASIC's internal symbol table so that no arrays (See Section 8) or
strings (See Section 7) are defined. Used in Direct mode.
Format: REM text
Example:
10 REM ROUTINE TO CALCULATE X
This command and the text following it are for the user's information only. It is
ignored by the computer. However, it is included in a LIST along with the other
numbered lines. Any statement on the same numbered line which occurs after a
REM statement will be ignored.

RUN (RU.)
STOP (STO.)
Format: RUN [filespec]
Examples: RUN
RUN
"D:MENU"
This command causes the computer to begin executing a program. If no filespec
is specified,
the current RAM-resident program begins execution. If a filespec is
included, the computer retrieves the specified, tokenized program from the
specified file and executes it.
All variables are set to zero and all open files and peripherals are closed. All ar-
rays, strings, and matrices are eliminated and all sounds are turned off. Unless
the TRAP command is used, an error message is displayed if any error is
detected during execution and the program halts.
RUN
can be used in Deferred mode.
Examples:
19 PRINT
11
0VER At() OJ..IER AGAIN."
20 R~
Type RUN and press l;ljili;lli. To end, pressl:!dy.i:i.
To begin program execution at a point other than the first line number, type
GOTO followed by the specific line number, then pressl;liiili;!li,
Format: STOP
Example: 100 STOP
When the STOP command is executed in a program, BASIC displays the
message STOPPED AT LINE ___ , terminates program execution, and
returns to Direct mode. The STOP command does not close files or turn off
sounds, so the program can be resumed by typing CONT l;l§iii;lll.
Commands 11

NOTES
12 Not es