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A 6502 assembler with restricted functions

Project description

6502 Restricted Assembler

Python application Coverage Status

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:

ADC AND ASL BCC BCS BEQ BIT BMI BNE BPL BRK BVC BVS CLC
CLD CLI CLV CMP CPX CPY DEC DEX DEY EOR INC INX INY JMP
JSR LDA LDX LDY LSR NOP ORA PHA PHP PLA PLP ROL ROR RTI
RTS SBC SEC SED SEI STA STX STY TAX TAY TSX TXA TXS TYA

Undocumented:

ANC ARR ASR DCP ISC JAM LAS LAX RLA RRA SAX SBX SHA SHS
SHX SHY SLO SRE XAA - - - - - - - - -

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

Project details


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