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I T T Y B I T T Y C O M P U T E R S
TINY BASIC User Manual
Congratulations! You have received the first of what we hope
is a long line of low cost software for hobby computers. We are
operating on a low margin basis, and hope to make a profit on
volume. Please help us to stay in business by respecting the
Copyright notices on the software and documentation.
If you are in a hurry to try TINY BASIC, Appendix C will tell
you how to get on the air. Then come back and read the rest of this
manual --- most of it is useful information.
The TINY BASIC interpreter program has been extensively tested
for errors ("bugs"), but it would be foolish to claim of any program
that it is guaranteed bug-free. This program does come with a
"Limited Warranty" in that any errors discovered will be corrected in
the first 90 days. Catastrophic bugs will be corrected by
automatically mailing out corrected versions to all direct mail
customers and local dealers. Minor bugs will be corrected by
request. In any case this warranty is limited to replacement of the
Program Tape and/or documentation, and no liability for consequential
damages is implied.
If you think you have found a bug, make a listing of the
program that demonstrates the bug, together with the run input and
output. Indicate on the listing what you think is wrong and what
version number you are running and your serial number (on the tape
leader). Mail this to:
ITTY BITTY COMPUTERS
P.0. Box 6539
San Jose, CA 95150
We will try to be responsive to your needs.
----------
(C) Copyright 1976 by Tom Pittman. All rights reserved.
"Itty Bitty" is a Trademark of the ITTY BITTY COMPUTERS Company.
1
TINY BASIC was conceived by the dragons at the People's
Computer Company (PCC), a non-profit corporation in Menlo Park CA.
and its implementation defined by Dennis Allison and others in the
PCC newspaper and an offshoot newsletter. The implementation of this
program follows the philosophy defined there. The reader is referred
to PCC v.4 Nos 1-3 for a discussion of the inner workings of this
software.
In keeping with the "small is good" philosophy, TINY BASIC
employs the two level interpreter approach (with its consequent speed
cost) so that the whole system occupies only 2K of program memory
(exclusive of user program; some versions are slightly larger).
With 1K of additional RAM small but useful user programs (50 lines or
less) may be accommodated. A system with 4K of RAM can contain the
interpreter and about 100 lines of user program.
TINY BASIC is offered in several versions for each processor.
One is designed to be used with an arbitrary operating system, and
executes out of low memory (e.g. 0100-08FF for the 6800). The other
versions are configured for unusual memory requirements of particular
operating systems. All are "clean" programs, in that they will
execute properly from protected memory (such as PROM). Direct
addressing is used for interpreter variables as much as possible, so
memory Page 00 is largely dedicated. In all cases the user programs
are placed at the end of that part of lower memory used by TINY, and
they may occupy all the remaining contiguous memory. Appendix D is a
a summary of the important low-memory addresses.
TINY BASIC is designed to be I/O independent, with all input
and output funneled through three jumps placed near the beginning of
the program. In the non-standard versions these are preset for the
particular operating system I/O, so the discussion to follow is
primarily concerned with the standard versions. For this
discussion, it is assumed that the interpreter begins at hex address
0100, though the remarks may be applied to other versions with an
appropriate offset.
Location 0106 is a JMP to a subroutine to read one ASCII
character from the console/terminal. Location 0109 is a JMP to a
subroutine to type or display one ASCII character on the
console/terminal. In both cases the character is in the A
accumulator, but the subroutine need not preserve the contents of the
other registers. It is assumed that the character input routine will
simultaneously display each character as it is input; if this is not
the case, the JMP instruction in location 0106 may be converted to a
JSR, so that each character input flows through the output subroutine
(which in this case must preserve A) before being fed to TINY.
Users with terminals using Baudot or some other non-ASCII code should
perform the character conversion in the Input and Output subroutines.
If your console is a CRT and/or you have no need to output or
display extra pad characters with each Carriage Return and Linefeed,
you may intercept these in the output routine to bypass their
display. Each input prompt by TINY is followed by an "X-ON"
character (ASCII DC1) with the sign bit set to 1 (all other
characters except rubout are output with the sign bit set to 0) so
these are also readily detected and deleted from the output stream.
Appendix C shows how to perform these tests.
A third subroutine provided by you is optional, and gives TINY
2
a means to test for the BREAK condition in your system. Appendix C
shows how this subroutine may be implemented for different types of
I/O devices. If you choose to omit this subroutine, TINY will assume
that a BREAK condition never happens; to include it, simply replace
locations 010C-010E with a JMP to your subroutine, which returns with
the break condition recorded in the Carry flag (1 = BREAK, 0 = no
BREAK). The Break condition is used to interrupt program execution,
or to prematurely terminate a LIST operation. Tiny responds to the
Break condition any time in the LIST, or just before examining the
next statement in program execution. If a LIST statement included
within a program is aborted by the Break condition, the Break
condition must be held over to the next statement fetch (or repeated)
to stop program execution also.
All input to Tiny is buffered in a 72 character line,
terminated by a Carriage Return ("CR"). Excess characters are
ignored, as signaled by ringing the console/terminal bell. When the
CR is typed in, Tiny will echo it with a Linefeed, then proceed to
process the information in the line. If a typing error occurs during
the input of either a program line or data for an INPUT statement,
the erroneous characters may be deleted by "backspacing" over them
and retyping. If the entire line is in error, it may be canceled
(and thus ignored) by typing the "Cancel" key. The Backspace code is
located near the beginning of the program (location 010F), and is
set by default to "left-arrow" or ASCII Underline (shift-O on your
Teletype). To change this to the ASCII Standard Backspace code (or
anything else you choose), the contents of location 010F may be
changed to the desired code. Similarly the Cancel code is located at
memory address 0110, and is set by default to the ASCII Cancel code
(Control-X). Four characters which may not be used for line edits
(Backspace or Cancel) are DC3 (hex 13), LF (0A), NUL (00), and DEL
(FF). These codes are trapped by the TINY BASIC input routines
before line edits are tested.
When Tiny ends a line (either input or output), it types a CR,
two pad characters, a Linefeed, and one more pad character. The pad
character used is defined by the sign bit in location 0111, and is
set by default to the "Rubout" or Delete code (hex FF; Location 0111
Bit 7 = 1) to minimize synchronization loss for bit-banger I/O
routines. The pad character may be changed to a Null (hex 00) by
setting the sign of location 0111 to 0. The remainder of this byte
defines the number of Pad characters between the CR and linefeed.
More than two pad characters may be required if large user programs
are to be loaded from tape (see comments on Tape Mode, below).
TINY BASIC has a provision for suppressing output (in
particular line prompts) when using paper tape for loading a program
or inputting data. This is activated by the occurrence of a Linefeed
in the input stream (note that the user normally has no cause to type
a Linefeed since it is echoed in response to each CR), and disables
all output (including program output) until the tape mode is
deactivated. This is especially useful in half-duplex I/O systems
such as that supported by Mikbug, since any output would interfere
with incoming tape data. The tape mode is turned off by the
occurrence of an X-OFF character (ASCII DC3, or Control-S) in the
input, by the termination of an executing program due to an error, or
after the execution of any statement or command which leaves Tiny in
the command mode. The tape mode may be disabled completely by
replacing the contents of memory location 0112 with a 00.
3
Memory location 0113 is of interest to those 6800 users with
extensive operating systems. Normally Tiny reserves 32 bytes of
stack space for use by the interpreter and I/O routines (including
interrupts). Up to half of these may be used by Tiny in normal
operation, leaving not more than 16 bytes on the stack for I/O. If
your system allows nested interrupts or uses much more than ten or
twelve stack bytes for any purpose, additional space must be
allocated on the stack. Location 0113 contains the reserve stack
space parameter used by Tiny, and is normally set to 32 (hex 20). If
your system requires more reserve, this value should be augmented
accordingly before attempting to run the interpreter.
All of these memory locations are summarized in Appendix D.
Note that there are no Input or Output instructions or interrupt
disables in the interpreter itself; aside from the routines provided
for your convenience (which you may connect or disconnect), your
system has complete control over the I/O and interrupt structure of
the TINY BASIC environment.
TINY BASIC is designed to use all of the memory available to it
for user programs. This is done by scanning all the memory from the
beginning of the user program space (e.g. 0900 for the standard 6800
version) for the end of contiguous memory. This then becomes the
user program space, and any previous contents may be obliterated.
If it is desired to preserve some part of this memory for machine
language subroutines or I/O routines, it will be necessary to omit
the memory scan initialization. This is facilitated in TINY BASIC by
the definition of two starting addresses. Location 0100 (or the
beginning of the interpreter) is the "Cold Start" entry point, and
makes no assumptions about the contents of memory, except that it is
available. Location 0103 is the "Warm Start" entry point, and
assumes that the upper and lower bounds of the user program memory
have been defined, and that the program space is correctly
formatted. The Warm Start does not destroy any TINY BASIC programs
in the program space, so it may be used to recover from catastrophic
failures. The lower bound is stored in locations 0020-0021 and the
upper bound is in locations 0022-0023. When using the Warm Start to
preserve memory, you should be sure these locations contain the
bounds of the user space. Also when using the Warm Start instead of
the Cold Start, the first command typed into TINY should be "CLEAR"
to properly format the program space.
STATEMENTS
TINY BASIC is a subset of Dartmouth BASIC, with a few
extensions to adapt it to the microcomputer environment. Appendix B
contains a BNF definition of the language; the discussion here is
intended to enable you to use it. When TINY issues a line prompt (a
colon on the left margin) you may type in a statement with or without
a line number. If the line number is included, the entire line is
inserted into the user program space in line number sequence, without
further analysis. Any previously existing line with the same line
number is deleted or replaced by the new line. If the new line
consists of a line number only, it is considered a deletion, and
nothing is inserted. Blanks are not significant to TINY, so blanks
4
imbedded in the line number are ignored; however, after the first
non-blank, non-numeric character in the line, all blanks are
preserved in memory.
The following are valid lines with line numbers!
123 PRINT "HELLO"
456 G O T O 1 2 3
7 8 9 PRINT "THIS IS LINE # 789"
123
32767 PRINT "THIS IS THE LARGEST LINE #"
1PRINT"THIS, IS THE SMALLEST LINE #"
10000 TINY BASIC DOES NOT CHECK
10001 FOR EXECUTABLE STATEMENTS ON INSERTION.
0 Is not a valid line number.
If the input line does not begin with a line number it is
executed directly, and must consist of one of the following statement
types:
LET GOTO REM
IF...THEN GOSUB CLEAR
INPUT RETURN LIST
PRINT END RUN
These statement types are discussed in more detail in the pages
to follow.
Note that all twelve statement types may be used in either the
Direct Execution mode (without a line number) or in a program
sequence (with a line number). Two of the statements (INPUT and RUN)
behave slightly differently in these two operating modes, but
otherwise each statement works the same in Direct Execution as within
a program. Obviously there is not much point in including such
statements as RUN or CLEAR in a program, but they are valid.
Similarly, a GOSUB statement executed directly, though valid, is
likely to result in an error stop when the corresponding RETURN
statement is executed.
EXPRESSIONS
Many of these statement types involve the use of EXPRESSIONS.
An Expression is the combination of one or more NUMBERS or VARIABLES,
joined by OPERATORS, and possibly grouped by Parentheses. There are
four Operators:
+ addition
- subtraction
* multiplication
/ division
These are hierarchical, so that in an expression without parentheses,
multiplication and division are performed before addition and
subtraction. Similarly, sub-expressions within parentheses are
evaluated first. Otherwise evaluation proceeds from left to right.
Unary operators (+ and -) are allowed in front of an expression to
denote its sign.
5
A Number is any sequence of decimal digits (0, 1, 2, ... 9),
denoting the decimal number so represented. Blanks have no
significance and may be imbedded within the number for readability if
desired, but commas are not allowed. All numbers are evaluated as
16-bit signed numbers, so numbers with five or more digits are
truncated modulo 65536, with values greater than 32767 being
considered negative. The following are some valid numbers (note
that the last two are equivalent to the first two in TINY):
0
100
10 000
1 2 3 4
32767
65536
65 636
A Variable is any Capital letter (A, B, ... Z). This variable
is assigned a fixed location in memory (two bytes, the address of
which is twice the ASCII representation of the variable name). It
may assume any value in the range, -32768 to +32767, as assigned to
it by a LET or INPUT statement.
The following are some examples of valid expressions:
A
123
1+2-3
B-14*C
(A+B)/(C+D)
-128/(-32768+(I*1))
(((((Q)))))
All expressions are evaluated as integers modulo 65536. Thus
an expression such as
N / P * P
may not evaluate to the same value as (N), and in fact this may be
put to use to determine if a variable is an exact multiple of some
number. TINY BASIC also makes no attempt to discover arithmetic
overflow conditions, except in the case of an attempt to divide by
zero (which results in an error stop). Thus all of the following
expressions evaluate to the same value:
-4096
15*4096
32768/8
30720+30720
TINY BASIC allows two intrinsic functions. These are:
RND (range)
USR (address,Xreg,Areg)
Either of these functions may be used anywhere an (expression) is
appropriate.
6
FUNCTIONS
RND (range)
This function has as its value, a positive pseudo-random number
between zero and range-1, inclusive. If the range argument is zero
an error stop results.
USR (address)
USR (address,Xreg)
USR (address,Xreg,Areg)
This function is actually a machine-language subroutine call to
the address in the first argument. If the second argument is
included the index registers contain that value on entry to the
subroutine, with the most significant part in X. If the third
argument is included, the accumulators contain that value on entry to
the subroutine, with the least significant part in A. On exit, the
value in the Accumulators (for the 6800; A and Y for the 6502)
becomes the value of the function, with the least significant part in
A. All three arguments are evaluated as normal expressions.
It should be noted that machine language subroutine addresses
are 16-bit Binary numbers. TINY BASIC evaluates all expressions to
16-bit binary numbers, so any valid expression may be used to define
a subroutine address. However, most addresses are expressed in
hexadecimal whereas TINY BASIC only accepts numerical constants in
decimal. Thus to jump to a subroutine at hex address 40AF, you must
code USR(16559). Hex address FFB5 is similarly 65461 in decimal,
though the equivalent (-75) may be easier to use.
For your convenience two subroutines have been included in the
TINY BASIC interpreter to access memory. If S contains the address
of the beginning of the TINY BASIC interpreter (256 for standard
6800, 512 for standard 6502, etc.), then location S+20 (hex 0114) is
the entry point of a subroutine to read one byte from the memory
address in the index register, and location S+24 (hex 0118) is the
entry point of a subroutine to store one byte into memory.
Appendix E gives examples of the USR function.
7
STATEMENT TYPES
PRINT print-list
PR print-list
This statement prints on the console/terminal the values of the
expressions and/or the contents of the strings in the print-list.
The print-list has the general form,
item,item... or item;item...
The items may be expressions or alphanumeric strings enclosed in
quotation marks (e.g. "STRING"). Expressions are evaluated and
printed as signed numbers; strings are printed as they occur in the
PRINT statement. When the items are separated by commas the printed
values are justified in columns of 8 characters wide; when semicolons
are used there is no separation between the printed items. Thus,
PRINT 1,2,3
prints as
1 2 3
and
PRINT 1;2;3
prints as
123
Commas and semicolons, strings and expressions may be mixed in one
PRINT statement at will.
If a PRINT statement ends with a comma or semicolon TINY BASIC
will not terminate the output line so that several PRINT statements
may print on the same output line, or an output message may be
printed on the same line as an input request (see INPUT). When the
PRINT statement does not end with a comma or semicolon the output is
terminated with a carriage return and linefeed (with their associated
pad characters). To aid in preparing data tapes for input to other
programs, a colon at the end of a print-list will output an "X-OFF"
control character just before the Carriage Return.
Although the PRINT statement generates the output immediately
while scanning the statement line, output lines are limited to 125
characters, with excess suppressed.
While the Break key will not interrupt a PRINT statement in
progress, the Break condition will take effect at the end of the
current PRINT statement.
The following are some examples of valid PRINT statements:
PRINT "A=";A,"B+C=";B+C
PR (one blank line)
PRI (prints the value of I)
PRINT 1,","Q*P;",",R/42:
8
INPUT input-list
This statement checks to see if the current input line is
exhausted. If it is, a question mark is prompted with an X-ON
control character, and a new line is read in. Then or otherwise, the
input line is scanned for an expression which is evaluated. The
value thus derived is stored in the first variable in the input-list.
If there are more variables in the input-list the process is
repeated. In an executing program, several values may be input on a
single request by separating them with commas. If these values are
not used up in the current INPUT statement they are saved for
subsequent INPUT statements. The question mark is prompted only when
a new line of input values is required. Note that each line of input
values must be terminated by a carriage return. Since expressions
may be used as input values, any letter in the input line will be
interpreted as the value of that variable. Thus if a program sets
the value of A to 1, B to 2, and C to 3, and the following statement
occurs during execution:
INPUT X,Y,Z
and the user types in
A,C,B
the values entered into X, Y, and Z will be 1, 3, and 2,
respectively, just as if the numbers had been typed in. Note also
that blanks on the input line are ignored by TINY, and the commas are
required only for separation in cases of ambiguity. In the example
above
ACB
could have been typed in with the same results. However an input,
line typed in as
+1 -3 +6 0
will be interpreted by TINY as a single value (=58) without commas
for separators. There is one anomaly in the expression input
capability: if in response to this INPUT, the user types,
RND+3
TINY will stop on a bad function syntax error (the RND function must
be of the form, RND(x)); but if the user types,
RN,D+3
the values in the variables R, N, and the expression (D+3) will be
input. This is because in the expression evaluator the intrinsic
function names are recognized before variables, as long as they are
correctly spelled.
Due to the way TINY BASIC buffers its input lines, the INPUT
statement cannot be directly executed for more than one variable at a
time, and if the following statement is typed in without a line
number,
INPUT A,B,C
the value of B will be copied to A, and only one value (for C) will
be requested from the console/terminal. Similarly, the statement,
INPUT X,1,Y,2,Z,3
will execute directly (loading X, Y, and Z with the values 1, 2, and
3), requesting no input, but with a line number in a program this
statement will produce an error stop after requesting one value.
If the number of expressions in the input line does not match
the number of variables in the INPUT statement, the excess input is
9
saved for the next INPUT statement, or another prompt is issued for
more data. The user should note that misalignment in these
circumstances may result in incorrect program execution (the wrong
data to the wrong variables). If this is suspected, data entry may be
typed in one value at a time to observe its synchronization with
PRINT statements in the program.
There is no defined escape from an input request, but if an
invalid expression is typed (such as a period or a pair of commas) an
invalid expression error stop will occur.
Because Tiny Basic does not allow arrays, about the only way to
process large volumes of data is through paper tape files. Each
input request prompt consists of a question mark followed by an X-ON
(ASCII DC1) control character to turn on an automatic paper tape
reader on the Teletype (if it is ready). A paper tape may be
prepared in advance with data separated by commas, and an X-OFF
(ASCII DC3 or Control-S) control character preceding the CR (a
Teletype will generally read at least one more character after the
X-OFF). In this way the tape will feed one line at a time, as
requested by the succession of INPUT statements. This tape may also
be prepared from a previous program output (see the PRINT
statement).
LET var = expression
var = expression
This statement assigns the value of the expression to the
variable (var). The long form of this statement (i.e. with the
keyword LET) executes slightly faster than the short form. The
following are valid LET statements:
LET A = B+C
I = 0
LET Q = RND (RND(33)+5)
10
GOTO expression
The GOTO statement permits changes in the sequence of program
execution. Normally programs are executed in the numerical sequence
of the program line numbers, but the next statement to be executed
after a GOTO has the line number derived by the evaluation of the
expression in the GOTO statement. Note that this permits you to
compute the line number of the next statement on the basis of program
parameters during program execution. An error stop occurs if the
evaluation of the expression results in a number for which there is
no line. If a GOTO statement is executed directly, it has the same
effect as if it were the first line of a program, and the RUN
statement were typed in, that is, program execution begins from that
line number, even though it may not be the first in the program.
Thus a program may be continued where it left off after correcting
the cause of an error stop. The following are valid GOTO
statements:
GOTO 100
GO TO 200+I*10
G 0 T 0 X
GOSUB expression
The GOSUB statement is like the GOTO statement, except that TINY
remembers the line number of the GOSUB statement, so that the next
occurrence of a RETURN statement will result in execution proceeding
from the statement following the GOSUB. Subroutines called by GOSUB
statements may be nested to any depth, limited only by the amount of
user program memory remaining. Note that a GOSUB directly executed
may result in an error stop at the corresponding RETURN. The
following are some examples of valid GOSUB statements:
GOSUB 100
GO SUB 200+I*10
RETURN
The RETURN statement transfers execution control to the line
following the most recent unRETURNed GOSUB. If there is no matching
GOSUB an error stop occurs.
11
IF expression rel expression THEN statement
IF expression rel expression statement
The IF statement compares two expressions according to one of
six relational operators. If the relationship is True, the statement
is executed; if False, the associated statement is skipped. The six
relational operators are:
= equality
< less than
> greater than
<= less or equal (not greater)
>= greater or equal (not less)
<>, >< not equal (greater or less)
The statement may be any valid TINY BASIC statement (including
another IF statement). The following are valid IF statements:
IF I>25 THEN PRINT "ERROR"
IF N/P*P=N GOTO 100
IF 1=2 Then this is nonsense
IF RND (100) > 50 THEN IF I <> J INPUT Q,R
END
The END statement must be the last executable statement in a
program. Failure to include an END statement will result in an error
stop after the last line of the program is executed. The END
statement may be used to terminate a program at any time, and there
may be as many END statements in a program as needed. The END
statement also clears out any saved GOSUB line numbers remaining, and
may be used for that purpose in the direct execution mode.
REM comments
The REM statement permits comments to be interspersed in the
program. Its execution has no effect on program operation, except
for the time taken.
12
CLEAR
The CLEAR statement formats the user program space, deleting
any previous programs. If included in a program (i.e. with a line
number) the program becomes suicidal when the statement is executed,
although no error results. If the Warm Start is used to initialize
the interpreter, this must be the first command given.
RUN
RUN,expression-list
The RUN statement is used to begin program execution at the
first (lowest) line number. If the RUN statement is directly
executed, it may be followed by a comma, followed by values to be
input when the program executes an INPUT statement.
If the RUN statement is included in a program with a line
number, its execution works like a GO TO first statement of the
program.
LIST
LIST expression
LIST expression,expression
The LIST statement causes part or all of the user program to be
listed. If no parameters are given, the whole program is listed. A
single expression parameter in evaluated to a line number which, if
it exists, is listed. If both expression parameters are given, all
of the lines with line numbers between the two values (inclusive) are
listed. If the last expression in the LIST statement evaluates to a
number for which there is no line, the next line above that number
which does exist (if any) is listed as the last line. Zero is not a
valid line number, and an error stop will occur if one of the
expressions evaluates to zero. A LIST statement may be included as
part of the program, which may be used for printing large text
strings such as instructions to the operator. A listing may be
terminated by the Break key.
If the terminal punch (or cassette recorder) is turned on for a
LIST operation, the tape may be saved to reload the program into TINY
at a later time.
The following are valid LIST statements:
LIST
LIST 75+25 (lists line 100)
LIST 100,200
LIST 500,400 (lists nothing)
13
A P P E N D I X A
ERROR MESSAGE SUMMARY
0 Break during execution
8 Memory overflow; line not inserted
9 Line number 0 not allowed
13 RUN with no program in memory
18 LET is missing a variable name
20 LET is missing an =
23 Improper syntax in LET
25 LET is not followed by END
34 Improper syntax in GOTO
37 No line to GO TO
39 Misspelled GOTO
40,41 Misspelled GOSUB
46 GOSUB subroutine does not exist
59 PRINT not followed by END
62 Missing close quote in PRINT string
73 Colon in PRINT is not at end of statement
75 PRINT not followed by END
95 IF not followed by END
104 INPUT syntax bad - expects variable name
123 INPUT syntax bad - expects comma
124 INPUT not followed by END
132 RETURN syntax bad
133 RETURN has no matching GOSUB
134 GOSUB not followed by END
139 END syntax bad
154 Can't LIST line number 0
164 LIST syntax error - expects comma
183 REM not followed by END
184 Missing statement type keyword
186 Misspelled statement type keyword
188 Memory overflow: too many GOSUB's ...
211 ... or expression too complex
224 Divide by 0
226 Memory overflow
232 Expression too complex ...
233 ... using RND ...
234 ... in direct evaluation;
253 ... simplify the expression
259 RND (0) not allowed
266 Expression too complex ...
267 ... for RND
275 USR expects "(" before arguments
284 USR expects ")" after arguments
287 Expression too complex ...
288 ... for USR
290 Expression too complex
293 Syntax error in expression - expects value
296 Syntax error - expects ")"
298 Memory overflow (in USR)
303 Expression too complex (in USR)
14
304 Memory overflow (in function evaluation)
306 Syntax error - expects "(" for function arguments
330 IF syntax error - expects relation operator
Other error message numbers may possibly occur if the
interpreter is malfunctioning. If this happens, check the program in
memory, or reload it, and try again.
Error number 184 may also occur if TINY BASIC is incorrectly
interfaced to the keyboard input routines. A memory dump of the
input line buffer may disclose this kind of irregularity.
15
A P P E N D I X B
FORMAL DEFINITION OF TINY BASIC
line ::= number statement CR
statement CR
statement ::= PRINT printlist
PR printlist
INPUT varlist
LET var = expression
var = expression
GOTO expression
GOSUB expression
RETURN
IF expression relop expression THEN statement
IF expression relop expression statement
REM commentstring
CLEAR
RUN
RUN exprlist
LIST
LIST exprlist
printlist ::=
printitem
printitem :
printitem separator printlist
printitem ::= expression
"characterstring"
varlist ::= var
var , varlist
exprlist ::= expression
expression , exprlist
expression ::= unsignedexpr
+ unsignedexpr
- unsignedexpr
unsignedexpr ::= term
term + unsignedexpr
term - unsignedexpr
term ::= factor
factor * term
factor / term
factor ::= var
number
( expression )
function
function ::= RND ( expression )
USR ( exprlist )
number ::= digit
digit number
separator ::= , ! ;
var ::= A ! B ! ... ! Y ! Z
digit ::= 0 ! 1 2 ! ... ! 9
relop ::= < ! > ! = ! <= ! >= ! <> ! ><
16
A P P E N D I X C
IMPLEMENTING I/O ROUTINES
COSMAC
COSMAC TINY occupies the same space as 6800 TINY -- 0100-08FF.
Similarly, the general parameters occupy 0020-00B7, as defined in
the manual. However, COSMAC TINY also uses locations 0011-001F to
contain copies of interpreter parameters and other run-time data; do
not attempt to use these locations while running TINY.
Like all Itty Bitty Computer software, COSMAC TINY contains no I/O
instructions (nor references to Q or EF1-4), no interrupt enables or
disables, and no references to an operating system. The three jumps
(LBR instructions) at 0106, 0109, and 010C provide all necessary
I/O, as defined in the manual. If you are using UT3 or UT4, you may
insert the following LBR instructions, which jump to the necessary
interface routines:
.. LINKS TO UT3/4
0106 C0076F LBR UTIN
0109 C00776 LBR UTOUT
010C C00766 LBR UTBRK
If you are not using the RCA monitor, you must write your own I/O
routines. For this the standard subroutine call and return linkages
are used, except that D is preserved through calls and returns by
storing it in RF.1. Registers R2-RB and RD contain essential
interpreter data, and if the I/O routines make any use of any of
them they should be saved and restored. Note however, that R2-R6
are defined in the customary way and may be used to nest subroutine
calls if needed. R0, R1, RC, RE and RF are available for use by the
I/O routines, as is memory under R2. Both the call and return
linkages modify X and the I/O data character is passed in the
accumulator ("D", not RD).
After connecting TINY to the I/O routines, start the processor at
0100 (the Cold Start). Do not attempt to use the Warm Start without
entering the Cold Start at least once to set up memory from
0011-0023. Any register may be serving as program counter when
entering either the Cold Start or the Warm Start.
The USR function works the same way as described in the manual,
except that the second argument in the call is loaded into R8, and
the third argument is loaded into RA with the least significant
byte also in the Accumulator. On return RA.1 and the accumulator
contain the function value (RA.0 is ignored). The machine language
subroutine must exit by a SEP R5 instruction. USR machine language
subroutines may use R0, R1, R8, RA, RC-RF, so long as these do not
conflict with I/O routine assignments. TINY BASIC makes no internal
use of R0, R1, RC, or RE.
RCA Corporation funded the development of COSMAC TINY BASIC, and it
is by RCA's permission that it is made available.
17
If you do not have access to a monitor in ROM with ASCII I/O
built in, you will have to write your own I/O routines. Most likely
you have something connected to a parallel port for the keyboard
input; output may be some parallel port also, or you may want to
use the 1861 video display for a gross dot-matrix kind of text
display. For the moment, let's assume you have parallel ports,
Port C (N=1100) for input, and port 4 (N=0100) for output. Assume
also that EF4 controls both input and output. This is the situation
you would have if you took an ordinary ELF and used the hex input
and display with the single "input" button to step through the
characters. You need for this configuration, two routines, which
might look something like this:
0106 C0 00E0 LBR KEYIN
0109 C0 00E7 LBR DISPL
...
00E0 3FE0 KEYIN BN4 *
00E2 E2 SEX 2
00E3 6C INP 4
00E4 37E4 B4 *
00E6 68 LSKP
00E7 3FE7 DISPL BN4 *
00E9 E2 SEX 2
00EA 73 STXD
00EB 52 STR 2
00EC 64 OUT 4
00ED 37ED B4 *
00EF D5 SEP 5
Of course if you have a keyboard on Port F you will change
the INP instruction to match; if the keyboard pulls EF3 down, then
you must change the first pair of BN4/B4 instructions to BN3/B3
instructions and change the LSKP to a NOP (C4 or E2). If your
input comes from some device that already displayed the character
typed, then change the LSKP to a Return (D5).
Similarly, if the output is to a different port you must
change the OUT instruction to fit it, and the second pair of BN4/B4
instructions to match the control line being used. Notice that
the LSKP instruction is only there to prevent your waiting on the
EF4 line twice for each keyin, and should be removed (changed to
a NOP) as soon as you connect up real input and output ports.
Many 1802 systems come equipped with a video output using
the 1861 chip. If you have this, you should get a copy of the
February and April 1979 issues of KILOBAUD MICROCOMPUTING (formerly
just KILOBAUD). I have a two-part article published in these two
issues which explains how to put text on the 1861 graphics display,
with particular emphasis on how to connect it to TINY BASIC.
So far I have not mentioned the Break test. If you leave
that part unchanged, Tiny will work just fine, but you cannot stop
a listing or a program that is getting too long. After you get
your keyboard and display connected up and working, you may want
to use EF4 (or some other flag) as a Break input. It is possible
to use the same flag for Break as for "input ready", if you want
Tiny to stop executing when you press a key on your keyboard (this
does not affect the INPUT instruction, which is obviously waiting
for that keyin). This code will do that:
010C C000F0 LBR BRKT
...
00F0 FC00 BRKT ADI 0
00F2 3FF6 BN4 EXIT
00F4 FF00 SMI 0
00F6 D5 EXIT SEP R5
Notice that the only function of this routine is to set the
Carry (DF) when EF4 is true (low) and clear it otherwise.
18
KIM
The Teletype I/O routines in the MOS Technology KIM system may
be used for the character input and output requirements of TINY BASIC
6502. The following break routine is included in Tiny to test the
serial data line at 1740; Since TINY BASIC 6502 does not use the
lower part of memory page 01, the break test routine is ORG'ed to
execute in that space:
; BREAK TEST FOR KIM
0100 AD4017 KIMBT LDA KTTY LOOK AT TTY
0103 18 CLC C=O IF IDLE
0104 300E BMI KIMX IDLE
0106 AD4017 LDA KTTY WAIT FOR END
0109 10FB BPL *-3
010B 200E01 KLDY JSR *+3
010E A9FF LDA #255 DELAY 2 RUBOUT TIMES
0110 20A01E JSR OUTCH
0113 38 SEC C=1 IF BREAK
0114 60 KIMX RTS
To run TINY BASIC 6502 load the paper tape into your Teletype
reader, type "L", and turn on the reader. Then key in the following
Jumps:
; JUMPS TO KIM
0206 4C5A1E JMP GETCH CHARACTER INPUT
0209 4CA01E JMP OUTCH CHARACTER OUTPUT
020C 4C0001 JMP KIMBT BREAK TEST
It is recommended that you save a copy of memory on tape
(0100-0114 and 0200-0AFF) before going any further. Or you may
prefer to save it on audio cassette. Set up the starting address for
Tiny at 0200, and type "G".
Because of the awkwardness of putting memory in the 4K gap left
in the KIM-1 system, an alternate version is available which executes
out of 2000-28FF. For this version the Cold Start is at 2000 and
other addresses are at 200x instead of 020x (cf. 010x in Appendix D).
JOLT or TIM
JOLT systems may not always have memory loaded in the space
from 0200 on up, so a special version has been prepared in which the
interpreter resides in the space 1000-18FF. This is the only
difference between the JOLT version and the KIM version, so if your
JOLT or TIM system has contiguous memory from Page 00 you may prefer
to use the KIM version to gain the extra memory space. Since the
serial data in the JOLT/TIM systems is not the same as KIM, a special
break test routine has also been provided for those systems:
; JOLT BREAK TEST
0115 A901 JOLBT LDA #1 LOOK AT TTY
0117 2C026E BIT JTTY
011A 18 CLC C=0 IF IDLE
19
011B F00E BEQ JOLTX IDLE
011D 2C026E BIT JTTY WAIT FOR END
0120 D0FB BNE *-3
0122 202501 JSR *+3 DELAY TWO CH TIMES
0125 A9FF LDA #255
0127 20C672 JSR WRT
012A 38 SEC C=1 = BREAK
012B 60 JOLTX RTS
To run, load the paper tape into your Teletype reader and type
"LH". Then key in the following Jumps:
; JUMPS TO JOLT/TIM
1006 4CE972 JMP RDT CHARACTER INPUT
1009 4CC672 JMP WRT CHARACTER OUTPUT
100C 4C1501 JMP JOLBT BREAK TEST
As with other versions, the Cold start is the beginning of the
program (1000).
MIKBUG
Systems that use MIKBUG (TM Motorola) for console I/O may use
the I/O routines in MIKBUG. The following break routine is provided
in Tiny to test the PIA at 8004:
* BREAK TEST FOR MIKBUG
B68004 BREAK LDA A PIAA LOOK AT PIA
0C CLC C=0 IF NONE
2B0D BMI EXIT
B68004 LDA A PIAA
2AFB BPL *-3 WAIT FOR END
8D00 BSR *+2
86FF LDA A #$FF DELAY ONE
BD0109 JSR TYPE CHARACTER TIME
0D SEC C=1 IF BREAK
39 EXIT RTS
To run, load the paper tape into your Teletype reader and type
"L". Then key in the following Jumps:
* JUMPS TO MIKBUG
ORG $0106
0106 7EE1AC JMP $E1AC CHARACTER INPUT
0109 7EE1D1 JMP $E1D1 CHARACTER OUTPUT
010C 7E08FD JMP $08FD BREAK TEST
It is recommended that you save a copy of memory on tape
(0100-08FF) before going any further. Set the starting address in
A048-A049 to 0100 and type "G". For your convenience the Cold Start
entry leaves the Warm start entry set up in the Mikbug stack, so that
after a reset a simple "G" command will result in a Warm start and
preserve the user programs.
20
OTHER
For standard systems (and for special systems with I/O other
than that provided), subroutines must be supplied by the user to
interface TINY to the operator. For ACIA input or output the
following routines may be used, or they may serve as examples for
your coding (6800 opcodes are shown). They should be assembled for
your ACIA address, and in some memory location which is not
contiguous with the TINY BASIC user program memory (which may be
destroyed by the Cold Start). If nothing else is available,
locations 00D8-00FF are not used by Tiny and may be used for this
purpose.
*
* ACIA I/O
*
B6XXXX BREAK LDA A ACIA
47 ASR A CHECK FOR TYPEIN
2406 BCC BRX NO, NOT BREAK
B6XXXY LDA A ACIA+1 GET IT
2601 BNE BRX NOT NULL IS BREAK
0C CLC IGNORE NULLS
39 BRX RTS
B6XXXX INPUT LDA A ACIA
47 ASR A
24FA BCC INPUT WAIT FOR A CHARACTER
B6XXXY LDA A ACIA+1 GET IT
36 OUTPUT PSH A SAVE CHARACTER
B6XXXX LDA A ACIA
8402 AND A #2 WAIT FOR READY
27F9 BEQ OUTPUT+1
32 PUL A
B7XXXY STA A ACIA+1 OUTPUT CHARACTER
39 RTS
Note that this routine will accept any non-null character
typein as a break. Alternatively we could look at the Framing Error
status, but if a character has been input this status will not show
up until that character is read in, rendering it ineffective in some
cases. Nulls are excepted as break characters since one or more of
them may follow the carriage return in an input tape, and still be
pending. Note that for this to work properly, the pad character
defined in location 0111 should be set to NULL (hex 00).
The 6800 "R" version of TINY BASIC includes these routines in
the code, as shown here. Locations 08FA-08FC contain a JMP to the
break test at the beginning of this block. You should alter the ACIA
addresses to suit your system before using the subroutines.
21
CRT OR TVT
If a TV Typewriter is used for I/O it may be desirable to
remove excess control characters from the output stream. All
controls except Carriage Return may be removed by the following
instructions at the beginning of the output subroutine (6800 opcodes
shown):
39 RTS
810A OUTPUT CMP A #0A
2FFB BLE OUTPUT-1
Only nulls, Rubouts, X-ON and X-OFF may be deleted by changing the
CMP to a TST A. Nulls may be passed through by also changing the BLE
to a BMI.
Some TV Typewriters do not scroll up when the cursor reaches
the bottom of the screen, but rather wrap the cursor around to the
top of the screen, writing over the previously displayed data. With
this kind of display it is essential that the I/O routines (or the
hardware) clear to the end of the line whenever a CR-LF is output,
so that previous data does not interfere with the new. If your I/O
routines are fixed in ROM, some sort of preprocessor may be required
to recognize output CR's and convert them to the appropriate sequence
of control functions. It may also be necessary to trap input CR's
(suppressing their echo) since Tiny generally responds with both
another CR and a linefeed.
Some users prefer to concatenate all output into one "line" of
print, using the terminal comma or semicolon to suppress the line
breaks. Since TINY was designed to limit line lengths to less than
128 characters, if this sort of concatenation is attempted it will
appear that TINY has quit running. To eliminate the print
suppression the most significant two bits of the print control byte
(location 00BF in most versions) may be cleared to zero periodically
with the USR function or in the output driver routine. The least
significant three bits of this same byte are used for the "comma
spacing" in the PRINT statement, and should be left unaltered.
CASSETTE I/O
Officially, TINY only speaks to one peripheral--the console.
However a certain amount of file storage may be simulated by
attaching these peripherals (such as cassette systems) to the
character input and output routines. If the same electrical and
software interface is used this is very easy. Otherwise the I/O
drivers will require special routines to recognize control characters
in the input and output data for setting internal switches which
select one of several peripherals. The USR function may also be
used either to directly call I/O routines or to alter switches in
memory.
22
A P P E N D I X D
LOW MEMORY MAP
LOCATION SIGNIFICANCE
-------- ------------
0000-000F Not used by any version of TINY
0011-001F COSMAC version temporaries
0020-0021 Lowest address of user program space
0022-0023 Highest address of program space
0024-0025 Program end + stack reserve
0026-0027 Top of GOSUB stack
0028-002F Interpreter parameters
0030-007F Input line buffer & Computation stack
0080-0081 Random Number Generator workspace
0082-0083 Variable "A"
0084-0085 Variable "B"
... ...
00B4-00B5 Variable "Z"
00B6-00C7 Interpreter temporaries
00B8 Start of User program (PROTO)
00C8-00D7 Sphere parameters (not 0020-002F)
00D8-00FF Unused by standard version
0100 Cold Start entry point (6800)
0103 Warm Start entry point
0106-0108 JMP (or JSR) to character input
0109-010B JMP to character output
010C-010E JMP to Break test
010F Backspace code
0110 Line Cancel code
0111 Pad character
0112 Tape Mode Enable flag (hex 80 = enabled)
0113 Spare stack size
0114 Subroutine to read one Byte
from RAM to A (address in X)
0118 Subroutine to store A into RAM
at address in X
0900 Beginning of User program (6800)
Note that some of these addresses apply to the standard 6800 version.
For other versions addresses above 0100 should be read as addresses
above their respective starting address.
23
A P P E N D I X E
AN EXAMPLE PROGRAM
10 REM DISPLAY 64 RANDOM NUMBERS < 100 ON 8 LINES
20 LET I=0
30 PRINT RND (100),
40 LET I=I+1
50 IF I/8*8=I THEN PRINT
60 IF I<64 THEN GOTO 30
70 END
100 REM PRINT HEX MEMORY DUMP
109 REM INITIALIZE
110 A=-10
120 B=-11
130 C=-12
140 D=-13
150 E=-14
160 F=-15
170 X = -1
175 O = 0
180 LET S = 256
190 REMARK: S IS BEGINNING OF TINY (IN DECIMAL)
200 REM GET (HEX) ADDRESSES
210 PRINT "DUMP: L,U";
215 REM INPUT STARTING ADDRESS IN HEX
220 GOSUB 500
230 L=N
235 REM INPUT ENDING ADDRESS IN HEX
240 GOSUB 500
250 U=N
275 REM TYPE OUT ADDRESS
280 GOSUB 450
290 REM GET MEMORY BYTE
300 LET N = USR (S+20,L)
305 REM CONVERT IT TO HEX
310 LET M = N/16
320 LET N = N-M*16
330 PRINT " ";
335 REM PRINT IT
340 GOSUB 400+M+M
350 GOSUB 400+N+N
355 REM END?
360 IF L=U GO TO 390
365 L=L+1
370 IF L/16*16 = L GOTO 280
375 REM DO 16 BYTES PER LINE
380 GO TO 300
390 PRINT
395 END
399 PRINT ONE HEX DIGIT
400 PRINT O;
24
401 RETURN
402 PRINT 1;
403 RETURN
404 PRINT 2;
405 RETURN
406 PRINT 3;
407 RETURN
408 PRINT 4;
409 RETURN
410 PRINT 5;
411 RETURN
412 PRINT 6;
413 RETURN
414 PRINT 7;
415 RETURN
416 PRINT 8;
417 RETURN
418 PRINT 9;
419 RETURN
420 PRINT "A";
421 RETURN
422 PRINT "B";
423 RETURN
424 PRINT "C";
425 RETURN
426 PRINT "D";
427 RETURN
428 PRINT "E";
429 RETURN
430 PRINT "F";
431 RETURN
440 REM PRINT HEX ADDRESS
450 PRINT
455 REM CONVERT IT TO HEX
460 N = L/4096
470 IF L<0 N=(L-32768)/4096+8
480 GOSUB 400+N+N
483 LET N=(L-N*4096)
486 GOSUB 400+N/256*2
490 GOSUB 400+(N-N/256*256)/16*2
495 GOTO 400+(N-N/16*16)*2
496 GOTO=GOSUB,RETURN
500 REM INPUT HEX NUMBER
501 REM FORMAT IS NNNNX
502 REM WHERE "N" IS ANY HEX DIGIT
505 N=0
509 REM INPUT LETTER OR STRING OF DIGITS
510 INPUT R
520 IF R=X RETURN
525 REM CHECK FOR ERROR
530 IF R>9999 THEN PRINT "BAD HEX ADDRESS
531 REM NOTE ERROR STOP ON LINE 530 (ON PURPOSE!)
535 REM CONVERT INPUT DECIMAL DIGITS TO HEX
540 IF R>999 THEN N=N*16
545 IF R>99 THEN N=N*16
550 IF R>9 THEN N=N*16
25
555 IF R>0 THEN R=R+R/1000*1536+R/100*96+R/10*6
559 REM PICK UP NON-DECIMAL DIGIT LETTERS
560 IF R<0 THEN LET R=-R
565 REM ADD NEW DIGIT TO PREVIOUS NUMBER
570 LET N=N*16+R
580 GOTO 510
590 NOTE: DON'T NEED END HERE
1000 TO RUN RANDOM NUMBER PROGRAM, TYPE "RUN"
1010 IT WILL TYPE 8 LINES THEN STOP.
1020 TO RUN HEX DUMP PROGRAM TYPE "GOTO 100"
1030 IT WILL ASK FOR INPUT, TYPE 2 HEX ADDRESSES
1040 EACH TERMINATED BY THE LETTER X,
1050 AND SEPARATED BY A COMMA
1055 (TYPE ALL ZEROS AS LETTER OH).
1060 THE PROGRAM WILL DUMP MEMORY BETWEEN
1070 THOSE TWO ADDRESSES, INCLUSIVE.
1080 EXAMPLE:
1090 :GOTO 100
1100 DUMP: L,U? AO3EX,AO46X
1110 A03E EE FF
1120 A040 00 11 22 33 44 55 66
1130 IF THE RANDOM NUMBER PROGRAM
1140 IS REMOVED, OR IF YOU TYPE IN
1150 :1 GOTO 100
1160 THEN YOU CAN GET THE SAME DUMP BY TYPING
1170 :RUN,AO3EX,AO46X
1180 .
1190 NOTE THAT THIS PROGRAM DEMONSTRATES NEARLY
1200 EVERY FEATURE AVAILABLE IN TINY BASIC.
REMARK: TO FIND OUT HOW MUCH PROGRAM SPACE
REM... YOU HAVE LEFT, TYPE:
LET I=0
1 LET I=I+2
2 GOSUB 1
RUN
REMARK: AFTER A FEW SECONDS, THIS WILL STOP
REM... WITH AN ERROR; THEN TYPE:
END
PRINT "THERE ARE ";I;" BYTES LEFT"
REM: TO EXIT FROM TINY BASIC TO YOUR MONITOR/DEBUGGER,
LET S=256
REM (S AS IN LINE 180 ABOVE)
LET B=0
IF P=6800 THEN LET B=63
REM: B IS SWI OR BRK INSTRUCTION
LET A = USR (S+24,0,B) + USR (0)
REM: THE FIRST CALL STORES A BREAK IN 0000
REM... THE SECOND CALL JUMPS TO IT.
26
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