Skip to content

Latest commit

 

History

History
160 lines (116 loc) · 4.23 KB

GettingStarted.md

File metadata and controls

160 lines (116 loc) · 4.23 KB
Raw

Getting Started

Overview

The 6502.Net Assembler is a cross-assembler for several CPUs from the 8-bit era of computing including the Motorola 6800 and 6809, the MOS 6502 and its variants, the Intel 8080, and the Zilog Z80.

6502.Net is a multi-pass assembler that supports user comments, symbolic and macro assembly, as well as advanced features like conditional and iterative assembly. Its dialect and style generally follows that of the TASS/TMP assemblers, and to a lesser extent ca65.

This document does assume basic knowledge of assembly language, though the examples and explanations incorporating assembly code throughout should be easy to follow along even for the less familiar.

Usage

The executable requires at least one input file as an argument.

dotnet 6502.net.dll mygame.asm

Several inputs can be specified at a time, processed in the order they are listed. The output filename can be set with the -o/--output option.

6502.net.exe mygame.asm -o mygame.prg

If not set, the output filename defaults to a.out.

General Syntax

A typical assembly statement takes the form of:

label        instruction        operands

This format should feel familiar to anyone who has developed using other assemblers. Labels are optional in statements. Though a common requirement in other assemblers, a label does not to be followed by a colon :, though this is allowed.

Hello, World

A "Hello, World" example for a Commodore 8-bit computer demonstrates the major features of the language.

            // select output format
            .format "cbm"

            // common CBM symbols and routines
            .include "cbmlib.s"

            // macro for a BASIC loader
            .basicstub start 
start:
            ldx #0
-           lda helloMessage,x  // next char
            beq +               // if 0 finish
            jsr CHROUT          // output to screen
            inx
            jmp -
+           rts
helloMessage:
            .cstring "HELLO, WORLD!"

Statements are typically terminated by newline characters, but can also be separated inline by colons.

    lda #$41:jsr $ffd2:rts

There are five conditions under which a newline character does not terminate a statement.

// When preceded by a backslash:

    lda \
      #$41
    jsr \
    $ffd2
    rts

// After the operator in an infix expression:

    lda #$40 +
        1

// Inside an expression group, array declaration, or dictionary declaration:
    lda #(
        $41
    ) + 3

// After a comma in an expression or argument list:
    .string "hello",
            "world"

// Inside a multiline string:
   .string \
"""
    PRESS <RETURN>
    TO BEGIN
 """

Comments

Single-line

All characters after the first occurrence of // or ; are treated as comments and are ignored until the newline:

    lda #$41  ;load character 'A'
    jsr $ffd2 // output to screen

Multiline

All characters between /* and */, including newline characters, are comments and are not processed.

    /* 
    the following code
    will print the letter "A"
    to the screen
    */
    lda #$41
    jsr $ffd2

Case-sensitivity

By default, 6502.Net processes text case-insensitive.

    // both forms are acceptable
    lda #$41
    LDA #$41

Passing command-line option -C forces all tokens to be evaluated case-sensitive. This is useful for instance when you want to create symbols that are the same name but vary by case.

// with -C the two labels are different
Loop   lda #$41
loop   jsr $ffd2

Other Topics