Color BASIC

Color BASIC is the Microsoft-licensed BASIC interpreter built into the Dragon 32, Dragon 64, and TRS-80 Color Computer (CoCo) family. It's closely related to other Microsoft BASICs of the era — if you know Commodore BASIC V2, you'll recognise the structure immediately, though the keywords and hardware POKEs are different.

The CoCo extended its BASIC with an Extended Color BASIC ROM (on later models and the CoCo 2/3), which adds graphics, sound, and joystick commands.

Quick start in the IDE

Select Dragon 32 or TRS-80 CoCo 2 as the platform.
Choose the BASIC preset.
Write your program in the editor and Build — it loads into the emulated machine.

The basics

Like all Microsoft 8-bit BASICs, Color BASIC uses line numbers and GOTO/GOSUB for flow control:

10 CLS
20 PRINT "HELLO, DRAGON!"
30 FOR I=1 TO 5
40   PRINT "LINE"; I
50 NEXT I
60 END

CLS clears the screen — on the Dragon/CoCo it produces a distinctive green-on-black display in text mode.

Variables

Type	Suffix	Example	Notes
Float	(none)	`X = 3.14`	Default — slow
Integer	`%`	`X% = 100`	Faster; -32768 to 32767
String	`$`	`N$ = "HELLO"`	Variable length

Variable names can be longer than 2 characters (unlike Commodore BASIC V2), though only the first 2 characters are significant on many versions.

Hex constants use &H prefix: &H1000 = 4096.

Control flow

10 IF X% > 10 THEN PRINT "BIG" ELSE PRINT "SMALL"
20 FOR I=1 TO 10 STEP 2
30   PRINT I
40 NEXT I
50 GOSUB 500
60 GOTO 10

500 PRINT "IN SUBROUTINE"
510 RETURN

Screen and text

10 CLS               : REM Clear screen (default colour)
20 CLS 2             : REM Clear screen to colour 2 (background colour)
30 PRINT "HELLO"
40 PRINT @32, "COL 0, ROW 1"  : REM Print at screen position 32
                               : REM (screen is 32 cols, so pos 32 = row 1, col 0)

PRINT @position is the Dragon/CoCo equivalent of Commodore's POKE to screen RAM — it positions the cursor at a specific character position. Position 0 = top-left, 511 = bottom-right of the 32×16 text screen.

Graphics

Color BASIC's graphics commands work in semi-graphic modes overlaid on the text display:

10 PMODE 4,1         : REM Set graphics mode 4 (256x192, 2 colour), page 1
20 PCLS 0            : REM Clear graphics screen (colour 0)
30 SCREEN 1,1        : REM Show graphics screen
40 PSET (128,96),1   : REM Plot pixel at (128,96) in colour 1
50 PRESET (128,96)   : REM Clear pixel at (128,96)
60 LINE (0,0)-(255,191),1      : REM Draw a line
70 LINE (0,0)-(255,191),1,BF   : REM Draw a filled box
80 CIRCLE (128,96),50,1        : REM Draw a circle

Graphics mode table (Extended Color BASIC):

PMODE	Resolution	Colours
0	128×96	2 (from 4-colour set)
1	128×96	4
2	128×192	2
3	128×192	4
4	256×192	2

10 PMODE 3,1 : SCREEN 1,1 : PCLS 0
20 FOR A=0 TO 360 STEP 5
30   X = 128 + 80*COS(A*3.14159/180)
40   Y = 96 + 60*SIN(A*3.14159/180)
50   PSET (X,Y), 1
60 NEXT A

Sound — the PLAY command

One of Color BASIC's best features is the PLAY command — a music macro language built right into BASIC:

10 PLAY "CDEFGAB"    : REM Play a C major scale
20 PLAY "T2 L4 O2 CEGCE2"  : REM Tempo 2, quarter notes, octave 2
30 PLAY "MF"         : REM Music foreground (wait to finish)
40 PLAY "MB"         : REM Music background (continue while playing)

PLAY syntax:

Letter	Meaning
A–G	Musical notes
O n	Set octave (1–5)
L n	Set note length (1=whole, 4=quarter, 8=eighth, …)
T n	Set tempo (1=slow, 255=fast)
V n	Set volume (1–31)
P n	Pause (length same as note)
MF	Music foreground (blocking)
MB	Music background (non-blocking)

10 PLAY "T4 L4 O3 CEGCE"   : REM Simple arpeggio, foreground
20 PLAY "T8 MB L8 CDECCDEC" : REM Fast background melody
30 FOR I=1 TO 100 : NEXT I  : REM Do other work while music plays

Joystick input

10 X = JOYSTK(0)    : REM Left joystick X axis (0-63, centre=31)
20 Y = JOYSTK(1)    : REM Left joystick Y axis
30 X2 = JOYSTK(2)   : REM Right joystick X axis
40 Y2 = JOYSTK(3)   : REM Right joystick Y axis
50 IF STRIG(0) THEN PRINT "LEFT FIRE"   : REM Fire button
60 IF STRIG(2) THEN PRINT "RIGHT FIRE"

The joystick axes return 0–63, with 31 at centre. STRIG(n) returns -1 (TRUE) if the button is pressed, 0 if not.

10 CLS
20 X=20 : Y=10
30 PRINT @Y*32+X, "*"     : REM Draw player
40 PRINT @Y*32+X, " "     : REM Erase (overwrite with space)
50 JX = JOYSTK(0) - 31    : REM Joystick -31 to +31
60 JY = JOYSTK(1) - 31
70 IF JX > 10 THEN X=X+1
80 IF JX < -10 THEN X=X-1
90 IF JY > 10 THEN Y=Y+1
100 IF JY < -10 THEN Y=Y-1
110 X = X - (X<0)*X : X = X - (X>31)*(X-31)  : REM Clamp X 0-31
120 Y = Y - (Y<0)*Y : Y = Y - (Y>15)*(Y-15)  : REM Clamp Y 0-15
130 GOTO 30

POKE and PEEK — hardware access

10 POKE &H1000, 255  : REM Write to memory address $1000
20 X = PEEK(&H1000)  : REM Read from $1000

Hex addresses use &H prefix. Some useful addresses:

Address	Purpose
$FF00	PIA 0-A (keyboard row, DAC bit 7)
$FF01	PIA 0-A control
$FF02	PIA 0-B (joystick comparator, cassette)
$FF20	PIA 1-A (6-bit DAC, cassette output)
$FF22	PIA 1-B (VDG mode bits)

Calling machine code

10 FOR I=0 TO 5
20   READ B
30   POKE &H7E00+I, B  : REM Load 6809 ML at $7E00
40 NEXT I
50 EXEC &H7E00          : REM Call it

100 DATA 134,0,183,255,34,57  : REM CLRA, STA $FF22, RTS

EXEC address calls machine code (6809 JSR to that address). The code above stores 0 into the VDG mode register and returns.

Extended Color BASIC extras (CoCo 2 and later Dragon models)

DRAW — turtle-style drawing: DRAW "U50;R50;D50;L50" draws a square
PAINT — flood fill: PAINT (X,Y), colour
GET / PUT — sprite-style block graphics capture and restore
HSCREEN — extended high-res graphics modes
HSET / HRESET / HPSET / HPRESET — high-res pixel plotting

Performance tips

Use integer variables (%) — 4× faster than floats for arithmetic
EXEC machine code for timing-critical loops — even short 6809 routines are 50–100× faster than BASIC
POKE directly to screen instead of PRINT — POKE &H0400+pos, charcode is faster
Background music with MB — let PLAY "MB..." run sound while your game loop continues