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Tiny Basic VERY Small Basic interpreter, with ASM source.
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Tiny Basic VERY Small Basic interpreter, with ASM source.
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Contents of the TBASIC.DOC file








8086 TINY BASIC USER'S GUIDE





INTRODUCTION



The TINY BASIC language originated in the pages of Dr. DOBB'S
JOURNAL and PEOPLE'S COMPUTER COMPANY in late 1975 and early 1976. Fed
by the enthusiasm of early computer hobbyists and by the challenges
and oportunities created by the early microcomputer chips, the idea of
a tiny basic interpreter quickly gained popularity and acceptance. The
language was a stripped down version of the ever-popular Dartmouth
BASIC with the proviso that it be "useful" with a minimum of then very
expensive memory. Additionally, TINY BASIC had to be ROMable since
mass storage at that time consisted of reels of teletype punch paper
tape, often punched at the unbearably slow rate of ten characters per
second.

The TINY BASIC language supports a very limited subset of the
Dartmouth BASIC language. It does not compare at all with the large
floating point BASIC's that have been released for almost all eight
bit microcomputer chips. It does not support strings. Then, why 8086
TINY BASIC? Well, the size is still small (2700 bytes), it is
efficient and easy to learn, and it is still ROMable. All of this
implies that the language is still useful in at least two important
applications: education and dedicated control.

The present version of TINY BASIC is based on Li-Chen Wang's
Palo Alto 8080 TINY BASIC as published in the May 1976 issue of DR.
DOBB'S JOURNAL. Dr. Wang's version of TINY BASIC was chosen for its
remarkable resiliance and simplicity. It has been optimized for the
8086 and it takes advantage of the hardware multiply and divide that
the 8086 affords. Other enhancements include the use of the host
operating system's line editing facilities and the LOAD and SAVE
facilities, which, in the 8080 version, are due to unknown authors.
The 8086 implementation is due to Michael E. Sullivan of Financial
Software, 54 Grove Street, Haddonfield, NJ, 08033.




THE LANGUAGE


Numbers

In TINY BASIC, all number are integers and must be within the
range of -32767 .. 32767.





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Variables

There are 26 scalar variables donoted by the letters A through
Z. The one array variable is denoted by '@(I)'. Its dimension is
limited by the size of the TINY BASIC program. See the description of
the SIZE function.


Functions

There are five functions in TINY BASIC.

ABS(X) - Returns the absolute vaulue of the variable X.

INP(X) - Returns data read from input port X. (0<=X<=255)

PEEK(X)- Returns the contents of memory location X. (-32767<=X<=32767)

RND(X) - Returns a random number between 1 and X (inclusive).

SIZE - Returns the number of bytes left unused by the program.



Arithmetic and Comparison Operators

The following operators are supported:

/ - integer divide (fractional results not returned)

* - integer multiply

- - subtract

+ - add

> - compare if greater than

< - compare if less than

= - compare if equal to
NOTE: multiple assignment statements are not supported,
i.e., "LET A=B=O" is interpreted by TINY BASIC as
meaning "set A to the result of comparing B with O".

# - compare if not equal to

>= - compare if greater than or equal to

<= - compare if less than or equal to


The +,-,*, and / operations return a value within the range -32767 ..
32767. TINY BASIC works exclusively with decimal numbers. In order to
represent the full range of numbers between 0 and 0FFFFH the


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properties of two's complement arithemtic should be understood. For
example, in order to PEEK at memory location 0FFFFH, the parameter -0
should be used as the PEEK function argument. Notice that the PEEK
operation (as well as other address referenced operations) are all
relative to the current data segment, which should be the same as the
code segment.

All compare operations result in a 1 if the comparison is true
and a 0 if it is false.


Expressions

Expressions are formed with numbers, variables, and functions
with arithmetic and compare operators between them. + and - signs can
also be used at the beginning of an expression. The value of an
expression is evaluated from left to right, except that the * and /
operators are always given precedence, with + and -, and then the
compare operators following, in that order. Parentheses can be used
to alter the order of evaluation in the standard algabraic sense.


Statements

A TINY BASIC statement consists of a statement number between 1
and 32767 followed by one or more commands (see Commands below).
Commands in the same statement are seperated by a semi-colon ";".If
the "GOTO", "STOP", and "RETURN" commands are used then they must be
the last command in that statement.


Program

A TINY BASIC program consists of one or more statements. When
the direct command (see Direct Commands below) "RUN" is issued, the
statement with the lowest statement number is executed first, then the
one with the next lowest statement number, etc. The "GOTO", "GOSUB",
"STOP", and "RETURN" commands can alter this normal sequence. Within
any statement the execution takes place from left to right. The "IF"
command can cause remaining commands within the same statement to be
skipped.


Abbreviations and Blanks


TINY BASIC statements and commands may use blanks freely, except
that numbers, command key words, and function names may not have
embedded blanks.

All TINY BASIC command key words and function names may be
abbreviated by following the abbreviation with a period. For example,
"PR.", "PRI.", and "PRIN." all stand for "PRINT". The word "LET" in
the LET command may be ommited.



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Editor


TINY BASIC contains a useful text editor for entering and
correcting TINY BASIC programs. All of the line editing features of
the host operating system are used. In order to correct an existing
TINY BASIC statement, that statement must be re-entered. Statements
may be deleted by simply typing their statement number, followed by a
CR. Corrections may be verified by typing LIST nnnn and striking the
control-X key to terminate the LIST process.




ERROR MESSAGES


There are only three error messages in TINY BASIC. When an error
is encountered the error message itself is printed, followed by the
statement causing the program error with a "?" inserted at the point
where the error is detected. Control is then passed to the TINY BASIC
monitor. A synopsis of the three error conditions follow.


-- WHAT?

WHAT?
210 P?TINT "THIS"

WHAT? indicates that TINY BASIC did not understand the statement
or command. In the example above, the command PRINT was mistyped on
statement number 210.


-- HOW?

HOW?
260 LET A=32000+5000?

HOW? indicates that TINY BASIC understands but cannot execute
the statement or command. In the example above, the sum of the numbers
exceeds 32767.


-- SORRY

SORRY

SORRY indicates that TINY BASIC understand but cannot execute
the statement or command due to insufficient memory. One cure is to
rephrase the TINY BASIC program in acceptable abbreviations.






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STATEMENT COMMANDS


TINY BASIC statement commands are listed below with examples.
Remember that commands can be concatenated with semi-colons. In order
to store any given statement, you must precede that statement with a
statement number between 1 and 32767. Statement numbers are NOT shown
in the examples.


LET command

LET A=234-5*6;A=A/2;X=A-100;@(X+9)=A-1

The LET command assigns the value of an expression to the
specified variable. In the example above, the variable "A" assumes
the value of the expression "234-5*6", or "204". Then the variable "A"
assumes the value "102". Next, the variable "X" is set to the value of
the expression "A-100", or "2". The last command assigns the value
"101" to the array variable "@(11)". The "LET" portion of the LET
command is optional, i.e., the following examples are true:

A=10
C=5*3/5;C=C*5


REM Command

REM ANYTHING CAN BE WRITTEN AFTER "REM"

The REM command is ignored by TINY BASIC. It is used by
experienced programmers to comment BASIC programs. A program comment
is used by programmers to remind themselves of the logic of a program
section. All good programs are invariably commented.


PRINT Command

PRINT

PRINT will cause a carriage-return (CR) and a line-feed (LF) on
the output device.

PRINT A*3+1,"ABC"

This form of the PRINT command will print the value of the
expression A*3+1 on the output device, followed by the string ABC on
the same line. Note that single (') or double quotes (") may be used
to denote character strings, but that pairs must be mached.

PRINT A*3+1,"ABC",

This form of the PRINT command will produce the same results as
the previous example except that the normal CR-LF is inhibited by the
trailing comma at the end of the statement. This allows other PRINT


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commands to print on the same line.

PRINT A,B,#3,C,D,E,#10,F,G

This form of the PRINT command demonstrates format control. The
format character # is used to indicate the number of leading spaces to
be printed before a number. The default number is 6. Once the # format
is invoked it is active for the remainder of the statement unless
overridden by a subsequent format specifier, as in the example.

PRINT 'ABC',\,'XXX'

The back-slash (\) character is used to cause a CR without a LF.
In this example, the string ABC is printed followed by the string XXX
on top of the original ABC.


INPUT Command


INPUT A,B

The INPUT statement is used to acquire input data during program
execution. In the example above, TINY BASIC will print A: and wait
for a number to be typed at the console terminal. Next, TINY BASIC
will print B: and wait for another number to be typed at the console
terminal. In this example the variables A and B will assume the values
of the appropiate input values. The INPUT statement will accept
expressions as well as numbers as input.

INPUT 'WHAT IS THE WEIGHT'A,"AND SIZE"B

In this example TINY BASIC will print the string WHAT IS THE
WEIGHT: and wait for operator input. Next, the string AND SIZE: will
be printed, on the same line, and TINY BASIC will wait for operator
input.

INPUT A,'STRING',\,"ANOTHER STRING",B

TINY BASIC will react to the back-slash character (\) in this
example in the same fashion as in the PRINT command. The second string
will overwrite the first string STRING.


IF Command

IF A
The IF command works with the comparison operators (enumerated
above) to check the validity of the specified comparison condition. In
this example, if the comparison A commands in the statement are executed. However, if the comparison
tests false, then the balance of the commands in the statement are NOT
executed and control passes to the statement with the next highest
statement number.


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IF A
This example illustrates a common use of the IF command and the
GOTO (see below) command. If the comparison tests true control is
passed to statement number 100, otherwise execution passes to the
statement with the next highest statement number.


GOTO Command

GOTO 120

This statement is used to modify the normal sequence of
execution of TINY BASIC statements. In this example, control is passed
unconditionally to statement number 120. The GOTO command cannot be
followed by a semi-colon and other commands within the same statement.
It must appear as the last command in any given statement.

GOTO A*10+B

This form of the GOTO is called a "computed GOTO". In this case,
control is passed to the statement number represented by the
expression that follows "GOTO".


GOSUB Command

GOSUB 120

The GOSUB command is used to invoke a subroutine at the
specified statement number (120 in the example). Control is passed to
statement number 120 and execution continues. A RETURN command (see
below) is used, within the subroutine, to cause TINY BASIC to pass
control to the statement that immediatly follows the GOSUB command
that caused the subroutine to execute. The GOSUB command cannot be
followed by any other commands within the same statement and it must
be the last command within any given statement. GOSUB commands can be
nested, limited by the size of the stack space (see below).

GOSUB A*10+B

In this example, the subroutine at the statement number equal to
the value of the expression is executed. This form of the statement
will cause a different subroutine to be executed depending upon the
value of the expression that follows "GOSUB".


RETURN Command


RETURN

The RETURN command causes execution to resume at the statement
that follows the GOSUB that caused the current subroutine to be
executed. It must be the last command of any given statement.


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FOR Command

FOR X=1 TO 10
PRINT 'HELLO'
NEXT X

The FOR command is used to set up execution loops. In the TINY
BASIC program segment above the statement PRINT 'HELLO' is executed 10
times since it is placed between the FOR statement and the NEXT
statement. The NEXT X statement (see below) has the effect of
incrementing X by one and passing control to the FOR statement. If the
new value of X is still less than or equal to 10, the TINY BASIC
statements between FOR and NEXT are executed again. This process
repeats until X is incremented past the loop termination value (10 in
the example above).

FOR X=1 TO 10 STEP 2
PRINT 'HELLO'
NEXT X

In the above variant of the FOR command the loop increment has
been changed from 1 (the default) to 2 by means of the STEP clause. In
this case, the program fragment would only print HELLO five times if
executed.

FOR commands can be nested, that is, one FOR loop can contain
other FOR loops provided that the loop variables (the variable X in
the examples) are diferent,. If a new FOR command with the same loop
variable as that of an old FOR command is encountered, the old FOR
will be terminated.


NEXT Command

NEXT X

The NEXT command is part of the FOR command and is used to cause
loop variables to be incremented by the increment specified by the
STEP clause (default is 1) and to pass control to the appropiate TINY
BASIC FOR loop. The variable specified by the NEXT command (X in the
example) is used to specify the correct FOR loop.


POKE Command

POKE A,B

The POKE command is used to place data B into memory address A.
This command may be repeated as follows:

POKE A,B,C,D

In the above example, data B is placed in memory location A, then data


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D is placed in memory location C. All variables may be expressions. Be
careful not to POKE TINY BASIC itself!


USR Command

USR(I,J)

The USR Command is actually a built-in TINY BASIC subroutine
call that permits linkage to machine language subroutines. All 8086
registers are available for use by the machine language subroutine. It
is the responsibility of the machine language routine to execute a RET
instruction. In the example above, a machine language routine at
address I is called. J is an optional parameter that, if present, will
be passed in register BX to the subroutine.


WAIT Command

WAIT I,J,K

The WAIT command is used to cause TINY BASIC execution to pause
and wait for a specified value at an 8086 input port. In the example
above, the value at input port I is read, exclusive OR'd with the
value of the expression J, and the result is then AND'd with the value
of expression K. WAIT will return only if the final result is
non-zero. WAIT provides an easy-to-use mechanism to cause TINY BASIC
to pause its execution and wait for a specified external event. J is
assumed to be 0 if not specified.


STOP Command

STOP

This command stops the execution of a TINY BASIC program and
passes control to the TINY BASIC monitor. It can appear many times in
a program but it must be the last command in any given statement.




DIRECT COMMANDS


Direct commands are those commands that can be invoked only by
the operator when TINY BASIC is in command mode (i.e. in response to
the '>' prompt). All statement commands (those listed above) can be
invoked while in command mode. Typing a control-C while in command or
monitor mode will cause TINY BASIC to terminate. Control is then
passed to the host operating system monitor.

Recall that a statment consists of a statement number followed
by one or more commands. If the statement number is missing, or if it
is 0, the command will be executed immediatly after typing the


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terminating CR. The following commands can be used as direct commands;
they CANNOT be used as part of a TINY BASIC statement.


RUN Command

RUN

The RUN command causes execution of the stored TINY BASIC
program. Execution will commence at the lowest numbered statement and
continue until there are either no more statements to execute or a
STOP command is found. A long TINY BASIC program may be terminated by
typing control-X at the console. This passes control the the TINY
BASIC monitor. A control-C may be typed at any time also, then TINY
BASIC is terminated and control is passed to the host operating
system.


LIST Command

LIST

The LIST command is used to display the current TINY BASIC
program on the operator's console. The statements will be listed in
numerical order. If LIST is followed by an expression (e.g. LIST 200)
the listing will commence with statements following the specified
statement, inclusive.


NEW Command

NEW

The NEW command deletes the current program from TINY BASIC's
memory.


SAVE Command

SAVE FILENAME

The SAVE command saves the current TINY BASIC program on the
logged in disk with the specified filename FILENAME. The default
filetype is ".TBI". If there is insufficient room on the disk, the
SAVE command responds with "HOW?".


LOAD Command

LOAD FILENAME

The LOAD command loads the specified TINY BASIC program from the
logged in disk into the program area. Any program residing within TINY
BASIC prior to the LOAD operation is lost. If the specified program is
not found on the disk, or if there is insufficient room for the


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program, LOAD responds with "HOW?". The filetype is assumed to be
".TBI".


BYE Command

BYE

The BYE command terminates TINY BASIC. Control is passed back to
the host operating system.




TINY BASIC OPERATION


TINY BASIC is initiated from the host operating system's command
mode like any other transient command. TINY BASIC will sign-on,
announce 'OK', and then prompt '>' awaiting operator interaction. An
example follows:

A:TBASIC

8086 TINY BASIC V1.0

OK
>

In the example above the program 'TBASIC.COM' was found on the
logged-in disk ('A' in the example). TINY BASIC then commenced
execution by first announcing itself and then prompting '>' for
operator input.

TINY BASIC utilizes all of the host operating system's line
editing facilities. For example, if an operator wished to cancel a
line typed to TINY BASIC, he need only type a control-X, etc. If hard
copy of a TINY BASIC session is desired, control-P and control-N will
toggle the printer, if it exists.

At present, saved TINY BASIC programs can be edited only with
the internal TINY BASIC editor. Programs prepared by an external
editor can not be read by TINY BASIC.














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