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

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

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