GB Basic V1.06 Documentation

 GB Basic is a floating-point BASIC interpreter for GameBoy that
allows you to write & execute programs up to 7.5K bytes in size.
Currently string variables are not supported, but may be in the
future.

 Long variable names are not supported. Variable names may be
a letter or a letter and a number.

The following commands are supported:

ABS(x)           -       Return the absolute value of x.

AUTO             -       Enable Auto load & run program on reset.
                         (Note: Use AUTO command last since SAVE
                          disables auto mode.)

CLEAR            -       Clear all variables.

CLS              -       Clear the screen

COLOR x          -       Set drawing color to x. 0=Black, 1=Dark Gray,
                         2=Light Gray, 3=White, & 4=XOR. (Defaults
                         to XOR on program execution.)

COS(x)           -       Return the cosine of x given in radians.

DIM              -       Only single dimension arrays are currently
                         supported. If not explicitly defined by a
                         DIM statement, it is assumed to be a size
                         of 10 upon first reference.

DATA x,...       -       Data in program.
        
DELAY            -       Delay from 1 to 65535 milliseconds.

END              -       End program.

FOR/NEXT         -       Program loop.       

FREE             -       Display remaining amount of free memory.

GOSUB            -       Execute a subroutine.

GOTO             -       Goto specific line.

IF/THEN          -       Conditional execution.

INPUT            -       Input data from user.

INT(x)           -       Returns the integer of x.

KEYPAD(x)        -       If x=0, the following bits are returned
                         if that button is pressed.
                           128 - Start    8 - Down
                            64 - Select   4 - Up
                            32 - B        2 - Left
                            16 - A        1 - Right
                         If x>0, then x is ANDed with the bits
                         above. If the result = zero, 0 is returned.
                         If result <> zero, a 1 is returned.

LET              -       Assign a value to a variable. (Optional)

LINE x1,y1,x2,y2 -       Draw a line on the screen using COLOR.
                         (0<=x<=127,0<=y<=119)

LIST [x][-][x]   -       List lines of the program. Starting and/or
                         ending line numbers are optional.

LOAD             -       Load program from battery-backed RAM.

LOCATE           -       Position cursor with coordinates Y,X.

PEEK(x)          -       Return value of a memory location x.

POINT x,y        -       Draw a point on the screen using COLOR.
                         (0<=x<=127,0<=y<=119)

POKE x,y         -       Write value y to a memory location x.

PRINT            -       Print to screen.

READ             -       Read data contained in DATA statements.

REM              -       Remark. Also ' is supported.

RENUM            -       Renumber program.

RESTORE          -       Set DATA pointer to a specific line number. If
                         no line number present, beginning of program.

RETURN           -       Return from subroutine.

RND(x)           -       Returns a random number between 0 and 1.
                         x is ignored.

RUN              -       Execute program.

SAVE             -       Save program to battery-backed RAM.

SCREEN x         -       If x=0, set text mode. If x=1, set graphics mode.

SGN(x)           -       Returns 1 if x > or = 0. Else returns value -1.

SIN(x)           -       Return the sine of x given in radians.

SOUND x,y        -       Generate a sound of frequency x for y milliseconds.
                         If y=65535, sound will stay on infinitely. If y=0,
                         sound is turned off.

SQR(x)           -       Returns the square root of x.

STEP             -       Used with FOR for specifying increment.

STOP             -       Same as end but displays line number last executed.

TAB(x)           -       Used with PRINT command for moving cursor to
                         column x.

TAN(x)           -       Returns the tangent of x given in radians.


Revision History
----------------

V1.0  - Original release
V1.01 - Rearranged on-screen keyboard.
        Reassigned key controls.
        Fixed exponent display problem.
V1.02 - Completed RENUM routine.
        Added restore [line#] ability.
        Added pointer at $80 to key table to allow others
         to modify this table for different external keyboards.
        Added hex entry of numbers using prefix &h.
V1.03 - Fixed 'cursor disappear' when arrow buttons pressed.
        Greatly speeded up CLS command.
        Added SCREEN, POINT, & LINE routines.
        Break now works for lines that GOTO themselves.
        Rearranged on-screen keyboard again for faster entry.
V1.04 - Select & Start are BOTH now required to break.
        This was done to allow individual buttons to be pressed
        and read with the new KEYPAD command.
        Added COLOR command.
V1.05 - Added AUTO command.
        Credit screen now disappears after ~10 seconds.
V1.06 - Fixed bugs in LIST options. Up & down buttons now
        speed up or slow down LIST command. Pressing break
        now halts LIST command.
        Added SOUND command.