asm68

This is an interactive MC6800 assembler for WOZNIAC-68, inspired by KRUSADER.

Usage

The assembler may be run by starting execution at the assembler load address (e.g., using F000R when running from ROM).

The assembler prints a prompt (?) to indicate it is ready to accept a command.

The following commands are supported:

• N - input new program
• L - list program
• A - assemble program
• D - disassemble memory

Commands are executed immediately, without the need to enter a carriage return.

Source Code Format

The assembler is line oriented. A program consists of a sequence of lines, one statement per line. Statements consist of up to four fields (columns):

1. label
2. mnemonic
3. operand
4. comment

A field may be empty. Empty fields at the end of the line may be omitted.

If a field begins with *, or if the mnemonic field is empty, the rest of the line is treated as a comment.

When inputting a new program, a space or tab character causes the assembler to advance to the next field until the end of line is reached. An exception to this is that spaces are treated literally within strings (FCC directive). A carriage return causes the assembler to advance to the next line. Escape causes the assembler to exit program entry mode and return to the prompt.

An example program is provided in tests/hello.s.

Limitations

• Parentheses are not allowed in expressions
• There is no operator precedence in expressions; the order evaluation is strictly left-to-right.
• Expressions containing operators may not contain a forward reference.

Motorola Freeware Cross Assembler Compatibility

The assembler provides a degree of source compatibility with the Motorola Freeware PC-Compatible 8-Bit Cross Assembler for the M6800 (M6800 Freeware Assembler).

Unless otherwise specified, the assembler generally follows the source conventions of the M6800 Freeware Assembler.

Differences

• Fields must be separated by exactly one tab or space character
• All expressions evaluated as unsigned 16-bit.
• FCB,FDB do not accept lists containing null items (e.g. ,,).

Extensions

• . may be used as PC in expressions
• ; may be used instead of * to introduce comments

Unimplemented directives

In scope

• BSZ
• FILL
• RMB
• ZMB

Out of scope

• OPT
• PAGE

Unimplemented features

In scope

• * as PC in expressions
• @ octal prefix
• % binary prefix
• forward references in FCB directives (must be forced to 8-bit)

Out of scope

• $ in symbol name
• . in middle of symbol name
• \ line continuation character
• signed arithmetic, greater than 16 bits

Caveats

• The following errors are not caught and may produce undefined behavior:
  • Symbol redefinition
  • EQU directive without a label.
  • Undefined symbol referenced in FCB,FDB directive.
  • Use of forward reference in EQU or ORG directives.
  • Source or program buffer overflow.
• Support for signed division removed; tests have NOT been updated.

Memory Layout

8ka1rom variant

Address Range	Description
$0000..$00FF	Zero page variables (256B)
$0100..$01FF	6800 stack (256B)
$0200..$02FF	Keyboard buffer (256B)
$0300..$0BFF	Program buffer (2K+256B)
$0C00..$0DFF	Global symbol table (512B)
$0E00..$0EFF	Local symbol table (256B)
$0F00..$0FFF	Forward reference table (256B)
$E000..$EFFF	Source buffer (4K)
$F000..$FEFF	Assembler (3.75K)

8ka1ram variant

Address Range	Description
$0000..$00FF	Zero page variables (256B)
$0100..$01FF	6800 stack (256B)
$0200..$02FF	Keyboard buffer (256B)
$0300..$04FF	Program buffer (512B)
$0500..$0CFF	Source buffer (2K)
$0D00..$0DFF	Global symbol table (256B)
$0E00..$0EFF	Local symbol table (256B)
$0F00..$0FFF	Forward reference table (256B)
$E000..$EEFF	Assembler (3.75K)

w68rom variant

Address Range	Description
$0000..$00FF	Zero page variables (256B)
$0100..$01FF	6800 stack (256B)
$0200..$02FF	Keyboard buffer (256B)
$0300..$1FFF	Program buffer (7.25K)
$2000..$9FFF	Source buffer (32K)
$A000..$AFFF	Global symbol table (4K)
$B000..$BFFF	Local symbol table (4K)
$C000..$CFFF	Forward reference table (4K)
$F000..$FEFF	Assembler (3.75K)

w68ram variant

Address Range	Description
$0000..$00FF	Zero page variables (256B)
$0100..$01FF	6800 stack (256B)
$0200..$02FF	Keyboard buffer (256B)
$0300..$1FFF	Program buffer (7.25K)
$2000..$90FF	Source buffer (28.25K)
$9100..$9FFF	Assembler (3.75K)
$A000..$AFFF	Global symbol table (4K)
$B000..$BFFF	Local symbol table (4K)
$C000..$CFFF	Forward reference table (4K)

32kram variant

Address Range	Description
$0000..$00FF	Zero page variables (256B)
$0100..$01FF	6800 stack (256B)
$0200..$02FF	Keyboard buffer (256B)
$0300..$1FFF	Program buffer (7.25K)
$2000..$64FF	Source buffer (17.25K)
$6500..$6CFF	Global symbol table (2K)
$6D00..$6DFF	Local symbol table (256B)
$6E00..$70FF	Forward reference table (768B)
$7100..$7FFF	Assembler (3.75K)

Building From Source

UNIX-like Operating Systems

Building requires the following tools:

• GNU Make
• M6800 Freeware Assembler installed as /usr/local/bin/as0
• This version of Hex2bin-2.5 for mot2bin command.
• bintomon by Jeff Tranter for conversion from binary to wozmon hex listing.