6502

Introduction

Wanting to start sizecoding on a 6502 platform in this day and age can be tough.

So here is a bit of help to get you started:

The 6502 processor

The 6502 processor can be seen as the 8-bit micro ARM chip. It has only has 3 registers (Accumulator, X and Y registers) and a handful of instructions to work with.

Adressing modes

To be added.

Zero page

When using the 6502 for sizecoding, you'll mostly be working from zeropage

6502 Based Platforms

• Atari 8Bit - Atari 8-Bit Family (Atari XL/XE, etc.)
• Apple II - Apple II(e)
• Commodore 64 - Commodore 64
• BBC Micro - Acorn BBC Micro/Master/Electron.
• Atari Lynx - Atari Lynx Handheld

Generic 6502 sinus table generator

	ldx #0
	ldy #$3f
make_sine:
value_lo
			lda #0
			clc
delta_lo
			adc #0
			sta value_lo+1
value_hi
			lda #0
delta_hi
			adc #0
			sta value_hi+1
 
			sta sintab+$c0,x
			sta sintab+$80,y
			eor #$7f
			sta sintab+$40,x
			sta sintab+$00,y
 
			lda delta_lo+1
			adc #8
			sta delta_lo+1
			bcc nothing
			inc delta_hi+1
nothing
			inx
			dey
			bpl make_sine

General 6502 Resources

• 6502.org http://www.6502.org/
• 6502 instruction reference http://www.6502.org/tutorials/6502opcodes.html
• 6502 books http://retro.hansotten.nl/6502-sbc/
• 6502 Assembler tutorial https://dwheeler.com/6502/oneelkruns/asm1step.html
• Easy 6502 code tester https://skilldrick.github.io/easy6502/
• Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate