6502 Restricted Assembler

A 6502 assembler with restricted functions.

Install

pip install mos-6502-restricted-assembler

Usage

from asm_6502 import Assembler

code = """
START ORG $0080
      JMP START
"""
assembler = Assembler()
results = assembler.assemble(code, add_entry=False)
# Results will be `[(0x0080, [0x4C, 0x80, 0x00])]`
#     0x0080 is the offset of the codes, the following are the bytes generated by the assembler.

code = """
ORG $0080
JMP $abcd
"""
results = assembler.assemble(code)
# Results will be `[
#     (0x0080, [0x4C, 0xcd, 0xab]),
#     (0xFFFC, [0x80, 0x00]),
# ]`
# By default, the assembler will set to 0xFFFE/F the address of the first line that can be executed.

Instructions

List

Official:

Undocumented:

Pseudo

ORG $0080    ; The following codes will be generated from this offset
.BYTE $AB    ; Set to the current address $0080 with a byte $AB
.WORD $ABCD  ; Set to the current address $0081 with two bytes $CD and $AB
.END         ; This is equivelent to JMP *

Addressing

START ORG $0080
      .WORD *+3
      NOP                 ; Implied addressing
      JMP (START)         ; Indirect addressing
      LDA #10             ; Load $0A into the accumulator
      LDA #LO $ABCD       ; Load $CD into the accumulator
      LDA #HI $ABCD       ; Load $AB into the accumulator
      LDA $00             ; Load into accumulator from zero-page address $00
      LDA $10,X           ; Load into accumulator from zero-page address ($10 + X) % $0100
      LDX $10,Y           ; Load into X from zero-page address ($10 + Y) % $0100
      LDA $ABCD           ; Load into accumulator from address $ABCD
      LDA $ABCD,X         ; Load into accumulator from address $ABCD + X
      LDA $ABCD,Y         ; Load into accumulator from address $ABCD + Y
      LDA ($40,X)         ; Load into accumulator from the 2-byte address contained in ($40 + X) % $0100
      LDA ($40),Y         ; Load into accumulator from (the 2-byte address contained in $40) + Y

Special rules for zero-page addressing:

LDA $0010           ; This is not zero-page addressing as the input contains a word
LDA *               ; This is not zero-page addressing no matter what the current code address is
LDA LABEL           ; This is not zero-page addressing no matter where LABEL points to
LDA $FF+10-10       ; This is not zero-page addressing as the intermedidate result is greater than a byte