Difference between revisions of "6502"

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* Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate
 
* Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate
  
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== Atari 8-bit family ==
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== 6502 Based Platforms ==
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The systems in this family are: Atari 400, 800, 5200, 1200XL, 600XL, 800XL, 130XE, 65XE, 800XE and XEGS.<br />
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*'''[[Atari 8Bit]]''' - Atari 8-Bit Family (Atari XL/XE, etc.)
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*'''[[Apple II]]''' - Apple II(e)
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The Atari 8-bit systems consists of the 6502 with custom hardware for graphics and sound.
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*'''[[Commodore 64]]''' - Commodore 64
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*'''[[BBC Micro]]''' - Acorn BBC Micro/Master/Electron.
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=== Setting up ===
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*'''[[Atari Lynx]]''' - Atari Lynx Handheld
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Setting up your development platform for the Atari 8bit systems is quite easy, first get the following tools:
 
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* Assembler: MADS Assembler - This assembler has nice macros for creating Binaries and SNA snapshot files out of the box. You can download it at https://mads.atari8.info/
 
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* Emulator(s): I Found Altirra to work best for my usecase. Make sure to use the original Rev2 rom for best compatibility.
 
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==== Special Memory Adresses ====
 
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* FRAMECOUNTER_HIGH = 19
 
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* FRAMECOUNTER_LOW  = 20
 
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=== Video display ===
 
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Video display on the Atari 8bit systems use the ANTIC and GTIA chips. Information can be found here:
 
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* https://en.wikipedia.org/wiki/ANTIC
 
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* https://www.atariarchives.org/agagd/chapter1.php
 
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==== Sync with frame  ====
 
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<syntaxhighlight lang="6502">
 
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RTCLOK      equ $0012
 
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      lda RTCLOK+2
 
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waits
 
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      cmp RTCLOK+2
 
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      beq waits
 
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</syntaxhighlight>
 
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Or if you don't mind trashing RTCLOK
 
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<syntaxhighlight lang="6502">
 
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RTCLOK      equ $0012
 
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waits
 
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      lsr RTCLOK+2
 
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      bcc waits
 
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</syntaxhighlight>
 
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Which is two bytes shorter.
 
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==== Getting something on screen ====
 
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<syntaxhighlight lang="6502">
 
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;fill screen with charset,(88,89)=an address
 
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org $600; free 6th page:600-6ff
 
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ldy #0
 
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fl: tya
 
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sta(88),y
 
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iny
 
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bne fl
 
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jmp *
 
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</syntaxhighlight>
 
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To be added soon.
 
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<syntaxhighlight lang="6502">
 
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SDMCTL = $022f
 
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HPOSP0  = $d000
 
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SIZEP0  = $d008
 
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GRAFP0  = $d00d
 
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COLPM0  = $d012
 
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FRAMECOUNTER_HIGH = 19
 
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FRAMECOUNTER = 20
 
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WSYNC = $d40a
 
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VCOUNT = $d40b
 
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sinewave = $0600 ; to $06ff
 
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org $80
 
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main
 
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; disable all graphics/colors
 
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ldx #0
 
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stx SDMCTL
 
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ldy #$7f
 
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sty SIZEP0 ; size p0=127
 
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ldx #0
 
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ldy #$3f
 
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make_sine:
 
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value_lo
 
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lda #0
 
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clc
 
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delta_lo
 
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adc #0
 
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sta value_lo+1
 
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value_hi
 
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lda #0
 
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delta_hi
 
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adc #0
 
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sta value_hi+1
 
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sta sinewave+$c0,x
 
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sta sinewave+$80,y
 
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eor #$7f
 
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sta sinewave+$40,x
 
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sta sinewave+$00,y
 
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lda delta_lo+1
 
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adc #8
 
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sta delta_lo+1
 
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bcc nothing
 
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inc delta_hi+1
 
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nothing
 
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inx
 
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dey
 
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bpl make_sine
 
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updateloop:
 
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; vblank
 
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lda VCOUNT
 
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bne updateloop
 
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; clear graphics
 
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sta HPOSP0
 
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sta GRAFP0
 
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ldy #0
 
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lda #47
 
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sta COLPM0
 
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yloop:
 
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tya          ; graphics shape = y
 
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sta WSYNC
 
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sta GRAFP0
 
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; a = sin(frame+y)+48
 
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tya
 
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adc FRAMECOUNTER
 
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tax
 
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lda sinewave,x
 
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adc #48
 
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sta HPOSP0
 
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                iny
 
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                bne yloop
 
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jmp updateloop
 
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run main
 
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</syntaxhighlight>
 
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=== Sound ===
 
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The Atari 8-bit use the POKEY chip to generate sound.
 
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* https://en.wikipedia.org/wiki/POKEY
 
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==== BASIC ====
 
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<syntaxhighlight lang="6502">
 
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; from Analog, 1985-09,pp.25-32
 
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*=$2000
 
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AUDF1=$D200
 
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AUDC1=$D201
 
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AUDCTL=$D208
 
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SKCTL=$D20F
 
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.MACRO SOUND ; voice,pitch,dist,vol;,dur
 
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lda #%2
 
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sta AUDF1+2*%1
 
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    lda #[[%3 * 16] | %4] ;lda #[[%3 shl 4] or %4]
 
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    sta AUDC1+2*%1
 
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.ENDM
 
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lda #0
 
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sta AUDCTL
 
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lda #3
 
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sta SKCTL
 
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SOUND 0,121,10,8
 
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jmp *
 
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</syntaxhighlight>
 
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==== Make some noise ====
 
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To be added soon.
 
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=== Additional Resources ===
 
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Sizecoding resource for the Atari 8bit are:
 
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* Mapping the Atari https://www.atariarchives.org/mapping/
 
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* Atari 8bit Memory map https://www.atariarchives.org/mapping/memorymap.php
 
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* Fready's undocumented 6502 opcodes https://github.com/FreddyOffenga/6502
 
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* Atari OS Rev2 disassembly for MADS assembler https://github.com/ilmenit/A800-OS-XL-Rev2
 
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* Fready's github https://github.com/FreddyOffenga/
 

Revision as of 10:41, 8 April 2022

Introduction

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

6502.jpg

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

General 6502 Resources

6502 Based Platforms

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