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Documentation for Gordo's MC68000 Tiny BASIC version 1.0 This is an adaptation of Li Chen Wang's 'Palo Alto Tiny BASIC' for the Motorola MC68000 microprocessor. It includes more functions and program save and load. As distributed, it is set up for a Motorola MEX68KECB Educational Computer Board connected to a host CP/M computer. The source code should give you enough details to allow you to install it on a different system. If you have any problems, you can write to me at: Gordon Brandly R.R. 2 Fort Sask., AB, Canada T8L 2N8 This version for the Atari 520 ST translated by : Kenneth L. Hurley 1230 W 7th #3 Eugene, OR 97402 (503) 343-7285 The Language Numbers In this Tiny BASIC, all numbers are integers and must be in the range 2147483647 to -2147483648. Variables There are 26 variables denoted by the letters A through Z. There is also a single array @(I). The dimension of this array (i.e., the range of value of the index I) is set automatically to make use of all the memory space that is left unused by the program (i.e., 0 through SIZE/4, see SIZE function below). All variables and array elements are 4 bytes long. Functions There are 4 functions: ABS(X) gives the absolute value of X. RND(X) gives a random number between 1 and X (inclusive). SIZE gives the number of bytes left unused by the program. PEEK(X) gives the value of the byte at memory location X. Arithmetic and Compare Operators / Divide. (Note that since we have integers only, 2/3=0) * Multiply. - Subtract. + Add. > Greater than. (comparison) < Less than. (comparison) = Equal to. (comparison) Note that to certain versions of BASIC "LET A=B=0" means "set both A and B to 0". To this version of Tiny BASIC, it means "set A to the result of comparing B with 0". <> Not equal to. (comparison) >= Greater than or equal to. (comparison) <= Less than or equal to. (comparison) +, -, *, and / operations result in values between -2147483647 and 2147483647. (-2147483648 is also allowed in some cases.) All compare operators result in a 1 if true and a 0 if not true. 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 * and / are always done first, and then + and - , and then compare operators. Parentheses can also be used to alter the order of evaluation. Note that compare operators can be used in any expression. For example: 10 LET A=(X>Y)*123+(X=Y)*456+(X<Y)*789 20 IF (U=1)*(V<2)+(U>V)*(U<99)*(V>3) PRINT "Yes" 30 LET R=RND(100), A=(R>3)+(R>15)+(R>56)+(R>98) In line 10, A will be set to 123 if X>Y, to 456 if X=Y, and to 789 if X<Y. In line 20, the "*" operator acts like a logical AND, and the "+" operator acts like a logical OR. In line 30, A will be a random number between 0 and 4 with a prescribed probability distribution of: 3% of being 0, 15-3=12% of being 1, 56-15=41% of being 2, 98-56=42% of being 3, and 100-98=2% of being 4. Program Lines A Tiny BASIC line consists of a line number between 1 and 65534 followed by one or more commands. Commands in the same line are separated by a colon ":". "GOTO", "STOP", and "RETURN" commands must be the last command on any given line. Program A Tiny BASIC program consists of one or more lines. When a direct command "RUN" is issued, the line with the lowest number is executed first, then the one with the next lowest line number, etc. However, the "GOTO", "GOSUB", "STOP", and "RETURN" commands can alter this normal sequence. Within a line, execution of commands is from left to right. The "IF" command can cause the remaining commands on the same line to be skipped over. Commands Tiny BASIC commands are listed below with examples. Remember that multiple commands can be put on one line if colons separate them. In order to store the line, you must also have a line number at the beginning of the line. (The line number and multiple-command lines aren't shown in the examples. REM or REMARK Command REM anything goes This line will be ignored by Tiny BASIC. LET Command LET A=234-5*6, A=A/2, X=A-100, @(X+9)=A-1 Will set the variable A to the value of the expression 234-5*6 (i.e. 204), set the variable A (again) to the value of the expression A/2 (i.e. 102), set the variable X to the value of the expression A-100 (i.e. 2), and then set the variable @(11) to 101 (where 11 is the value of the expression X+9 and 101 is the value of the expression A-1). LET U=A<>B, V=(A>B)*X+(A<B)*Y Will set the variable U to either 1 or 0 depending on whether A is not equal to or is equal to B; and set the variable V to either X, Y or 0 depending on whether A is greater than, less than, or equal to B. Print Command PRINT Will cause a carriage-return (CR) and a line-feed (LF) on the output device. PRINT A*3+1, "abc 123 !@#", ' cba ' Will print the value of the expression A*3+1 (i.e. 307), the string of characters "abc 123 !@#" and the string" cba ", and then a CR-LF. Note that either single or double quotes can be used to quote strings, but pairs must be matched. PRINT A*3+1, "abc 123 !@#", ' cba ', Will produce the same output as before, except that there is no CR-LF after the last item printed. This enables the program to continue printing on the same line with another "PRINT". PRINT A, B, #3, C, D, E, #10, F, G Will print the values of A and B in 11 spaces, the values of C, D, and E in 3 spaces, and the values of F and G in 10 spaces. If there aren't enough spaces specified for a given value to be printed, the value will be printed in full anyway. PRINT 'abc',_,'xxx' Will print the string "abc", a CR without a LF, and then the string "xxx" (over the "abc") followed by a CR-LF. INPUT Command INPUT A, B When this command is executed, Tiny BASIC will print "A:" and wait to read in an expression from the input device. The variable A will be set to the value of this expression, then "B:" is printed and variable B is set to the value of the next expression read from the input device. Note that whole expressions as well as numbers can be entered. INPUT 'What is the weight'A, "and size"B This is the same as the command above, except the prompt "A:" is replaced by "What is the weight:" and the prompt "B:" is replaced with "and size:". Again, both single and double quotes can be used as long as they are matched. INPUT A, 'string',_, "another string", B The strings and the "_" have the same effect as in "PRINT". POKE Command POKE 4000+X,Y This command puts the value produced by expression "Y" into the byte memory location specified by the expression "4000+X". CALL Command CALL X This command will call a machine language subroutine at the address specified by the expression "X". All of the CPU's registers (except the stack pointer) can be used in the subroutine. IF Command IF A<B LET X=3: PRINT 'this string' This will test the value of the expression A<B. If it isn't zero (i.e. if it is true), the rest of the commands on this line will be executed. If the value of the expression is zero (i.e. if it is not true), the rest of this line will be skipped over and execution continues on the next line. Note that the word "THEN" is not used. GOTO Command GOTO 120 Will cause execution to jump to line 120. Note that the "GOTO" command cannot be followed by a colon and other commands. It must be ended with a CR. GOTO A*10+B Will cause the execution to jump to a different line number as computed from the value of the expression. GOSUB and RETURN Commands GOSUB 120 Will cause execution to jump to line 120. GOSUB A*10+B Will cause execution to jump to different lines as computed from the value of the expression A*10+B. RETURN A RETURN command must be the last command on a line and must be followed by a CR. When a RETURN command is encountered, it will cause execution to jump back to the command following the most recent GOSUB command. GOSUB's can be nested with a depth limited only by the stack space. FOR and NEXT Commands FOR X=A+1 TO 3*B STEP C-1 The variable X is set to the value of the expression A+1. The values of the expressions (not the expressions themselves) 3*B and C-1 are remembered. The name of the variable X, the line number and the position of this command within the line are also remembered. Execution then continues the normal way until a NEXT command is encountered. The step can be positive, negative or even zero. The word STEP and the expression following it can be omitted if the desired step is +1. NEXT X The name of the variable X is checked with that of the most recent FOR command. If they do not agree, then that FOR is terminated and the next recent FOR is checked, etc. When a match is found, this variable will be set to its current value plus the value of the step expression saved by the FOR command. The updated value is then compared with the value of the TO expression also saved by the FOR command. If this within the limit, execution will jump back to the command following the FOR command. If this is outside the limit, execution continues following the NEXT command itself. FOR's can also be nested with a depth limited only by the stack space. If a new FOR command with the same control variable as that of an old FOR command is encountered, the old FOR will be terminated automatically. STOP Command STOP This command stops the execution of the program and returns control to direct commands from the console. It can appear many times in a program but must be the last command on any given line, i.e. it cannot be followed by a colon and other commands. BYE Command Will return you to the resident monitor program or operating system. (Tutor in the case of the ECB.) Direct Commands As defined earlier, a line consists of a line number followed by commands. If the line number is missing, or if it is 0, the commands will be executed after you have typed the CR. All the commands described above can be used as direct commands. There are five more commands that can be used as direct commands but not as part of a program line: RUN Will start to execute the program starting at the lowest line number. LIST Will print out all the lines in numerical order. LIST 120 Will print out all the lines in numerical order starting at line 120. NEW Will delete the entire program. SAVE Will save the present program on the storage device you provide. Details on installing this device are given in the source code. As set up for the MEX68KECB Educational Computer Board, this command will send the program out to the host computer in an easily-stored text form. It isn't, however, pure program text as the line numbers are stored in hexadecimal. LOAD Will delete the program in memory and load in a file from your storage device. Stopping Program Execution The execution of the program or listing of the program can be stopped by pressing the control-C key on the console. Additionally, a listing can be paused by pressing control-S, and then pressing any key to continue. Abbreviations and Blanks You may use blanks freely within a program except that numbers, command key words, and function names cannot have embedded blanks. You may truncate all command key words and function names and follow each by a period. "P.", "PR.", "PRI.", and "PRIN." all stand for "PRINT". The word LET in LET commands may also be omitted. The shortest abbreviations for all the key words are as follows: A.=ABS C.=CALL F.=FOR GOS.=GOSUB G.=GOTO IF=IF I.=INPUT L.=LIST LO.=LOAD N.=NEW N.=NEXT P.=PEEK PO.=POKE P.=PRINT REM=REMARK R.=RETURN R.=RND R.=RUN S.=SAVE S.=SIZE S.=STEP S.=STOP TO=TO no key word = LET Error Reports There are only three error conditions in Tiny BASIC. The line with the error is printed out with a question mark inserted at the point where the error is detected. (1) "What?" means it doesn't understand you. For example: What? 260 LET A=B+3, C=(3+4?. X=4 (2) "How?" means it understands you but doesn't know how to do it. How? 210 P?TINT "This" <- where PRINT is misspelled How? 310 LET A=B*C?+2 <- where B*C is larger than 2147483647 How? 380 GOTO 412? <- where 412 does not exist (3) "Sorry." means it understands you and knows how to do it but there isn't enough memory to accomplish the task. Error Corrections If you notice an error in your entry before you press the CR, you can delete the last character with the backspace (control-H) key or delete the entire line with control-X. To correct a line, you can retype the line number and the correct commands. Tiny BASIC will replace the old line with the new one. To delete a line, type the line number and a CR only. You can verify the corrections to line 'nnnn' by typing "LIST nnnn" and pressing the control-C key while the line is being printed.