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EDTASM+ Assembler Syntax Reference

Target Platform: TRS-80 Color Computer (CoCo) Assembler: Disk EDTASM+ (Tandy/Microsoft) CPU Support: Motorola 6809, HD6309

Overview​

EDTASM+ is the standard assembler for TRS-80 Color Computer development. It features a straightforward syntax with powerful macro capabilities and conditional assembly.

Key Characteristics:

  • Case-insensitive (traditional) or case-sensitive (modern implementations)
  • Column-oriented source format
  • Flexible delimiters for string constants
  • Rich set of assembler directives
  • Macro system with parameters and local labels

Source Line Format​

[label] [opcode] [operand] [;comment]

Field Rules:

  1. Label (Column 1+): Optional, up to 6 characters (original), longer in modern variants
  2. Opcode (after label or whitespace): Instruction mnemonic or directive
  3. Operand: Address, immediate value, or expression
  4. Comment: Preceded by semicolon (;) or asterisk (*) in column 1

Comments​

* Asterisk in column 1 = full line comment
        LDA     #10     ; Semicolon comment anywhere

Assembler Directives​

ORG - Set Origin Address​

Sets the assembly address for subsequent code.

        ORG     $0400           ; Start assembly at $0400
START   LDA     #0

Source: FLEX 6809 Assembler

END - End Assembly​

Marks the end of the source file.

        END     START           ; End, entry point at START

EQU - Equate Symbol​

Defines a constant symbol (cannot be redefined).

BUFSIZE EQU     256             ; Define constant
MAXVAL  EQU     BUFSIZE*2       ; Expression

Source: FLEX 6809 Assembler Directives

SET - Set Variable​

Defines a variable symbol (can be redefined).

COUNT   SET     0               ; Initial value
COUNT   SET     COUNT+1         ; Can change

FCB - Form Constant Byte​

Defines 8-bit data values.

        FCB     1,2,3,4,5       ; Multiple bytes
        FCB     $FF             ; Hex value
        FCB     %11110000       ; Binary value
        FCB     'A'             ; ASCII character
        FCB     255             ; Decimal value

Source: FLEX 6809 Directives

FDB - Form Double Byte​

Defines 16-bit word values (big-endian).

        FDB     $1234           ; Single word
        FDB     $1000,$2000     ; Multiple words
        FDB     START           ; Address of label
        FDB     START+10        ; Expression

FCC - Form Constant Characters​

Defines ASCII string with flexible delimiter.

        FCC     /Hello, World!/ ; Using slash delimiter
        FCC     "Double quotes" ; Using quotes
        FCC     'Single quotes' ; Using apostrophe
        FCC     |Any char|      ; Any non-alphanumeric

Note: First non-whitespace character after FCC is the delimiter.

Source: FLEX 6809 Directives

RMB - Reserve Memory Bytes​

Reserves uninitialized space.

BUFFER  RMB     256             ; 256 bytes of space
VARS    RMB     10              ; 10 bytes
STACK   RMB     $100            ; 256 bytes (hex)

Source: FLEX 6809 Directives

SETDP - Set Direct Page​

Informs assembler of Direct Page register value for optimization.

        SETDP   $10             ; Direct page is $10xx
        LDA     $50             ; Assembles as direct mode (DP:$50)

NAM - Name​

Sets program name (for listing).

        NAM     MYPROG

TTL/TITLE - Title​

Sets listing title.

        TTL     My Program V1.0

PAGE - New Page​

Forces page break in listing.

        PAGE

SPC - Space​

Inserts blank lines in listing.

        SPC     3               ; 3 blank lines

OPT - Options​

Controls listing options.

        OPT     MC              ; List macro calls
        OPT     NOMC            ; Don't list macro calls
        OPT     MD              ; List macro definitions
        OPT     MEX             ; List macro expansions
        OPT     L               ; Enable listing
        OPT     NOL             ; Disable listing

LIST/NOLIST - Listing Control​

Toggles listing output.

        LIST                    ; Enable listing
        ; ... code listed ...
        NOLIST                  ; Disable listing
        ; ... code not listed ...

Conditional Assembly​

COND/ENDC​

Basic conditional assembly.

DEBUG   EQU     1               ; Debug flag

        COND    DEBUG           ; Assemble if DEBUG != 0
        LDA     #$FF
        STA     DEBUGPORT
        ENDC

IF Family​

        IFEQ    TARGET          ; If TARGET == 0
        ; ...
        ENDIF

        IFNE    TARGET          ; If TARGET != 0
        ; ...
        ENDIF

        IFGT    COUNT-10        ; If COUNT > 10
        ; ...
        ELSE
        ; ...
        ENDIF

        IFGE    VALUE-5         ; If VALUE >= 5
        IFLT    SIZE-100        ; If SIZE < 100
        IFLE    LIMIT-50        ; If LIMIT <= 50

Macro System​

MACRO/ENDM​

Define reusable code blocks.

* Macro definition
DELAY   MACRO
        LDB     \\1             ; Parameter 1
\\.LOOP DECB                    ; Local label
        BNE     \\.LOOP
        ENDM

* Macro invocation
        DELAY   #10             ; Call with parameter

Parameters:

  • \\1 through \\9 - Positional parameters
  • \\@ - Unique ID for this invocation
  • \\.label - Local label unique to invocation

INCLUDE Directive​

Include external source files.

        INCLUDE os9.d           ; Include OS-9 definitions
        INCLUDE macros.asm      ; Include macro library

Note: INCLUDE allows splitting large projects into modules.

Number Formats​

        LDA     #10             ; Decimal (default)
        LDA     #$FF            ; Hexadecimal ($ prefix)
        LDA     #%11110000      ; Binary (% prefix)
        LDA     #'A'            ; ASCII character

Expressions​

EDTASM+ supports arithmetic expressions:

RESULT  EQU     (VALUE+10)*2    ; Arithmetic
        LDA     #BUFFER+OFFSET  ; Address arithmetic
        FDB     START-END       ; Subtraction

Operators:

  • +, - - Addition, subtraction
  • *, / - Multiplication, division
  • &, |, ^ - AND, OR, XOR (vasm extension)
  • <, > - Low byte, high byte extraction

Symbol Rules​

Valid characters:

  • Start: A-Z, a-z, _ (underscore)
  • Continue: A-Z, a-z, 0-9, _, $ (dollar sign in vasm-ext)

Case sensitivity:

  • Original EDTASM: case-insensitive
  • Modern implementations: case-sensitive by default, -nocase flag for compatibility

OS-9 Support​

System Calls​

        INCLUDE os9.d           ; OS-9 definitions

        LDA     #READ
        LDX     #FILENAME
        OS9     I$Open          ; System call
        BCS     ERROR

MOD Directive​

OS-9 module header (implementation-specific).

TypeLang EQU    $11
AttRev   EQU    $81

        MOD     MODEND,MODNAME,TypeLang,AttRev,START,MEMSIZE

MODNAME FCC     /MyProgram/
        FCB     $00
START   ; Code begins
MODEND  EQU     *

Differences from Other Syntaxes​

vs. Merlin (6502):

  • No colon before labels (EDTASM uses whitespace)
  • Different directive names (FCB vs ASC/HEX)
  • Macro syntax uses \\ prefix instead of ]
  • Case-insensitive by default

vs. AS6809/LWASM:

  • Similar directive set
  • EDTASM has richer macro system
  • Different local label syntax

Complete Example​

* Example EDTASM program for CoCo
* Print "Hello, World!" to screen

        ORG     $0400           ; Program starts at $0400

PUTCHR  EQU     $A002           ; ROM routine for char output

START   LDX     #MESSAGE        ; Point to message
LOOP    LDA     ,X+             ; Get character
        BEQ     DONE            ; Zero byte = end
        JSR     PUTCHR          ; Print it
        BRA     LOOP            ; Next character

DONE    RTS                     ; Return to BASIC

MESSAGE FCC     /Hello, World!/
        FCB     $0D             ; Carriage return
        FCB     $00             ; Null terminator

        END     START           ; End, entry at START

References​

Online Resources​

  • Disk EDTASM Remastered (Tandy) - Official Manual
  • 6809 Assembly Language Programming (Lance Leventhal)
  • TRS-80 Color Computer Technical Reference Manual

Implementation Reference​

  • vasm-ext EDTASM syntax module: ~/Projects/Vintage/tools/vasm-ext/syntax/edtasm/