Difference between revisions of "6502"

Latest revision as of 12:55, 8 April 2024

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

Difference between revisions of "6502"

Latest revision as of 12:55, 8 April 2024

Contents

Introduction

The 6502 processor

Adressing modes

Zero page

6502 Based Platforms

Generic 6502 sinus table generator

General 6502 Resources

Navigation menu

Personal tools

Namespaces

Variants

Views

More

Search

Navigation

Tools

@@ Line 16: / Line 16: @@
 When using the 6502 for sizecoding, you'll mostly be working from zeropage
-=== General 6502 Resources ===
+== 6502 Based Platforms ==
-* 6502.org http://www.6502.org/
+*'''[[Atari 8Bit]]''' - Atari 8-Bit Family (Atari XL/XE, etc.)
-* 6502 instruction reference http://www.6502.org/tutorials/6502opcodes.html
+*'''[[Apple II]]''' - Apple II(e)
-* 6502 books http://retro.hansotten.nl/6502-sbc/
+*'''[[Commodore 64]]''' - Commodore 64
-* 6502 Assembler tutorial https://dwheeler.com/6502/oneelkruns/asm1step.html
+*'''[[BBC Micro]]''' - Acorn BBC Micro/Master/Electron.
-* Easy 6502 code tester https://skilldrick.github.io/easy6502/
+*'''[[Atari Lynx]]''' - Atari Lynx Handheld
-* Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate
-== Atari 8-bit family ==
+== Generic 6502 sinus table generator ==
-The systems in this family are: Atari 400, 800, 5200, 1200XL, 600XL, 800XL, 130XE, 65XE, 800XE and XEGS.<br />
+<syntaxhighlight lang="">
-The Atari 8-bit systems consists of the 6502 with custom hardware for graphics and sound.
-=== Setting up ===
-Setting up your development platform for the Atari 8bit systems is quite easy, first get the following tools:
-* 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/
-* Emulator(s): I Found Altirra to work best for my usecase. Make sure to use the original Rev2 rom for best compatibility.
-==== Special Memory Adresses ====
-* FRAMECOUNTER_HIGH = 19
-* FRAMECOUNTER_LOW  = 20
-=== Video display ===
-Video display on the Atari 8bit systems use the ANTIC and GTIA chips. Information can be found here:
-* https://en.wikipedia.org/wiki/ANTIC
-* https://www.atariarchives.org/agagd/chapter1.php
-==== Sync with frame  ====
-<syntaxhighlight lang="6502">
-RTCLOK      equ $0012
-      lda RTCLOK+2
-waits
-      cmp RTCLOK+2
-      beq waits
-</syntaxhighlight>
-Or if you don't mind trashing RTCLOK
-<syntaxhighlight lang="6502">
-RTCLOK      equ $0012
-waits
-      lsr RTCLOK+2
-      bcc waits
-</syntaxhighlight>
-Which is two bytes shorter.
-==== Getting something on screen ====
-<syntaxhighlight lang="6502">
-;fill screen with charset,(88,89)=an address
- org $600; free 6th page:600-6ff
- ldy #0
-fl: tya
- sta(88),y
- iny
- bne fl
- jmp *
-</syntaxhighlight>
-To be added soon.
-<syntaxhighlight lang="6502">
-SDMCTL	= $022f
-HPOSP0  = $d000
-SIZEP0  = $d008
-GRAFP0  = $d00d
-COLPM0  = $d012
-FRAMECOUNTER_HIGH = 19
-FRAMECOUNTER = 20
-WSYNC	= $d40a
-VCOUNT	= $d40b
-sinewave	= $0600		; to $06ff
-		org $80
-main
-	; disable all graphics/colors
-	ldx #0
-	stx SDMCTL
-	ldy #$7f
-	sty SIZEP0	; size p0=127
 	ldx #0
 	ldy #$3f
@@ Line 117: / Line 40: @@
 			sta value_hi+1
-			sta sinewave+$c0,x
+			sta sintab+$c0,x
-			sta sinewave+$80,y
+			sta sintab+$80,y
 			eor #$7f
-			sta sinewave+$40,x
+			sta sintab+$40,x
-			sta sinewave+$00,y
+			sta sintab+$00,y
 			lda delta_lo+1
@@ Line 132: / Line 55: @@
 			dey
 			bpl make_sine
-updateloop:
-		; vblank
-		lda VCOUNT
-		bne updateloop
-		; clear graphics
-		sta HPOSP0
-		sta GRAFP0
-		ldy #0
-		lda #47
-		sta COLPM0
-yloop:
-		tya           ; graphics shape = y
-		sta WSYNC
-		sta GRAFP0
-		; a = sin(frame+y)+48
-		tya
-		adc FRAMECOUNTER
-		tax
-		lda sinewave,x
-		adc #48
-		sta HPOSP0
-                iny
-                bne yloop
-		jmp updateloop
-		run main
 </syntaxhighlight>
-=== Sound ===
+=== General 6502 Resources ===
-The Atari 8-bit use the POKEY chip to generate sound.
+* 6502.org http://www.6502.org/
-* https://en.wikipedia.org/wiki/POKEY
+* 6502 instruction reference http://www.6502.org/tutorials/6502opcodes.html
+* 6502 books http://retro.hansotten.nl/6502-sbc/
-==== BASIC ====
+* 6502 Assembler tutorial https://dwheeler.com/6502/oneelkruns/asm1step.html
-<syntaxhighlight lang="6502">
+* Easy 6502 code tester https://skilldrick.github.io/easy6502/
-; from Analog, 1985-09,pp.25-32
+* Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate
-*=$2000
-AUDF1=$D200
-AUDC1=$D201
-AUDCTL=$D208
-SKCTL=$D20F
-.MACRO SOUND ; voice,pitch,dist,vol;,dur
-	lda #%2
-	sta AUDF1+2*%1
-    lda #[[%3 * 16] | %4] ;lda #[[%3 shl 4] or %4]
-    sta AUDC1+2*%1
-.ENDM
- lda #0
- sta AUDCTL
- lda #3
- sta SKCTL
- SOUND 0,121,10,8
- jmp *
-</syntaxhighlight>
-==== Make some noise ====
-To be added soon.
-=== Additional Resources ===
-Sizecoding resource for the Atari 8bit are:
-* Mapping the Atari https://www.atariarchives.org/mapping/
-* Atari 8bit Memory map https://www.atariarchives.org/mapping/memorymap.php
-* Fready's undocumented 6502 opcodes https://github.com/FreddyOffenga/6502
-* Atari OS Rev2 disassembly for MADS assembler https://github.com/ilmenit/A800-OS-XL-Rev2
-* Fready's github https://github.com/FreddyOffenga/
-== Commodore 64 ==
-The Commodore system consists of a 6502-compatible MOS 6510 processor with custom hardware for graphics and sound.
-=== Setting up ===
-Setting up your development platform for the Commodore systems is quite easy, first get the following tools:
-* Assembler: To be added
-* Emulator(s): VICE is the way to go
-=== Memory map ===
-<syntaxhighlight lang="6502">
--1          $0-$1      PROCESSOR PORT REGISTERS, not usable as RAM
--255         $0-$FF     ZEROPAGE, mostly used by BASIC interpreter and Kernal
--511      $100-$1FF    SYSTEM STACK
--600      $200-$258    INPUT BUFFER
--630      $259-$276    FILE SYSTEM DATA
--640      $277-$280    KEYBOARD BUFFER, filled by Kernal ISR upon key presses
--678      $281-$2A6    VARIOUS KERNAL VARIABLES
--767      $2A7-$2FF    Unused (89 byte)
--779      $300-$30B    KERNAL VECTORS
--783      $30C-$30F    REGISTER VALUES A,X,Y,SR for SYS
--819      $310-$333    KERNAL VECTORS
--827      $334-$33B    Unused (8 byte)
--1019     $33C-$3FB    DATASETTE BUFFER
--1023     $3FC-$3FF    Unused (4 byte)
--2023     $400-$7E7    SCREEN MEMORY (25 lines times 40 columns)
--2039     $7E8-$7F7    Unused (16 byte)
--2047     $7F8-$7FF    SPRITE COSTUME POINTERS
-          $800         must contain a value of 0 so that the BASIC program can be RUN
--40959    $801-$9FFF   BASIC AREA (code, variables, arrays, strings)
--49151   $A000-$BFFF   BASIC ROM (unused RAM underneath)
--53247   $C000-$CFFF   UPPER RAM AREA (unused)
--53294   $D000-$D02E   VIC-II, memory-mapped graphics chip registers)
--54300   $D400-$D41C   SID, memory-mapped sound chip registers)
--56295   $D800-$DBE7   Color RAM, only lower 4 bits are stored, higher nibble undefined
--56319   $DBE8-$DBFF   Unused (24 half-bytes)
--56335   $DC00-$DC0F   CIA#1, memory-mapped I/O chip registers for keyboard, joystick, mouse, datasette, IRQ control
--56591   $DD00-$DD0F   CIA#1, memory-mapped I/O chip registers for serial bus, RS232, NMI control
--65535   $E000-$FFFF   KERNAL ROM
--65535   $FFFE-$FFFF   Execution address of interrupt service routine, can only be set if KERNAL is turned off
-</syntaxhighlight>
-For a detailed explanation of the C64 memory map check out [https://sta.c64.org/cbm64mem.html Commodore 64 memory map] on Joe Forster/STA homepage.
-=== Program file overhead ===
-A standard CBM file consists of a 2 byte loading address followed by the data that is placed into memory starting at this address. In addition, if your machine program should be able to be started with "RUN", you need a BASIC stub that is loaded into memory from $0801 to $080c, typically followed by your machine program:
-<syntaxhighlight lang="6502">
-*=$0801
-        .word $080b   ;address of next BASIC line
-        .word LINENR  ;line number, can be chosen between 0 and 63999
-        .byte $9e     ;token for SYS command
-        .byte $32,$30,$36,$31  ;address to jump to in ASCII code: "2061"
-        .byte $00     ;end of BASIC line
-        .word $0000   ;address of next BASIC line, $0000 means end of BASIC program
-start
-; your code here
-</syntaxhighlight>
-Together with the 2 byte load address, this makes an overhead of 14 byte for your program. To reduce this, you can
-* omit the BASIC line and tell users to start your program by directly entering "SYS ''address''"
-* save your program from $0802 on, the byte at $0801 is recovered automatically after loading by the relink function. This reduces your program file size by 1 byte
-* accept the loss and use the 2 byte establishing LINENR for something good, they are copied to zeropage addresses $39/$3a automatically, saving you the effort of initializing the addresses
-* use an autostart method (see below)
-Some compos also specify that the BASIC loader does not count towards the overall filesize, check the rules before you worry.
-=== Autostart ===
-Unlike the Commodore 128, the Commodore 64 has no dedicated built-in auto-boot feature, but it is possible to autorun a program after loading by specifying the load address so that it overwrites a vector or address that is called by the operating system. There are multiple possibilities:
-==== Overwriting  CHROUT vector at $326-$327 ====
-The vector at address $326-$327 points at the CHROUT routine, normally at address $F1CA.
-If you put the entry address of your program into $326/27, your code will be called when the operating system wants to print "READY." after loading.
-Note that the vector at address $328-$329 points at the STOP routine that checks the status of Stop key indicator. Since this routine is called multiple times before your code is done loading, its default value $F6ED needs to be preserved.
-Application example:
-<syntaxhighlight lang="6502">
-*=$0326
-        .word start
-        .byte $ed,$f6
-start
-; rest of code
-</syntaxhighlight>
-Together with the two byte load address, the overwritten CHROUT vector and the preserved STOP vector, your program file will have a deadweight of 6 byte: $26 $03 $0a $03 $ed $f6, less than half of the standard version with a BASIC stub with SYS
-Caveat:
-* If your program after $32a is longer than 214 byte, part of your program will load into the screen at $400. Thus, issuing a clear screen will overwrite your program. It is possible to move the screen memory somewhere else, but that requires storing a new value into address $D018, which when done with an LDA # / STA pair will cost you 5 byte
-* Since you changed the CHROUT pointer, standard KERNAL functions for printing won't work. For output of single characters, you can still use the direct address $F1CA. Alternatively, you can restore the vectors by calling $FD15, which will overwrite the memory $314 to $333 with the default values.
-==== Overwriting BASIC idle loop vector at $302-$303 ====
-After loading the program, the BASIC idle loop will be called. By overwriting the vector at $302/$303 it is possible to autostart your program. Since the memory before $302 can be safely overwritten, the program would be arranged so that $303 is the '''last''' address of your program. If your program requires a loop back to the start, the vector can be used as part of a JMP where the following two bytes are already there, saving one byte in comparison to a loop done with a branch command.
-Application example:
-<syntaxhighlight lang="6502">
-*=$304 - (end - start)
-start:
-        ;your code here
-        ; ...
-        jmp     start    ;the address for start lies in $302/$303, thus will be called by the Kernal after loading
-end:
-</syntaxhighlight>
-In cases where the vector has a practical use, the overhead in filesize is only the 2 byte loading address. For programs larger than 93 byte keep in mind that addresses before $2A7 are in use by the Kernal.
-==== Overwriting return address on stack at $1F8 ====
-When the load routine is called, the stack pointer is always at $FA at a stock C64. Thus the return address from the loading process is stored in memory address $F8 (low byte) and $F9 (high byte). During the loading routine, stack usage will clobber the stack below $1F8, but a program loaded to $1F8 and above will be fine and the overwritten address stored at $1F8/$1F9 will be called after loading.
-Application example:
-<syntaxhighlight lang="6502">
-*=$1F8
-        .word start-1   ;adjust for the RTS command pulling the address from stack and increasing it by 1
-start:
-        ;your code here
-</syntaxhighlight>
-For programs larger than 95 byte keep in mind that addresses after $259 are in use by the Kernal, you might overwrite some values here if you don't have disk operations, but better check the memory map beforehand.
-Together with the two byte load address and the overwritten address at $1F8/$1F9, your program file will have a deadweight of 4 byte when using this method.
-==== Putting your program into zeropage overwriting part of CHRGET ====
-CHRGET is a machine code routine for the BASIC interpreter that is placed in the zero page at $73-$8A. By putting your program at $7C and following, the CHRGET routine runs directly into your code.
-Application example:
-<syntaxhighlight lang="6502">
-*=$7C
-start:
-        ;your code here
-</syntaxhighlight>
-With this method, there is no need for a start address vector. The only deadweight in your program is the loading address. However, the zero page is a busy place, if your program extends beyond address $8f (that is it has more than 22 bytes on disk) you have to deal with some parts of your program being overwritten, for example, the status byte in $90 is set after loading.
-=== Video display ===
-Video display on the Commodore has the following video modes:
-* Standard text mode, 40x25 characters, 1 individual color per character, 1 common background color
-* Multicolor text mode, 40x25 characters, every two bits (fat pixel) define color: background, char, common color 1+2
-* Extended color text mode, 40x25 characters, 1 individual foreground color per character, 1 out of 4 background colors, only 64 chars
-* Hires bitmap, 320x200 pixels, an 8x8 field can have an individual foreground and an individual background color
-* Multicolor bitmap, 160x200 pixels, every two bits (fat pixel) define color: background, screen color lower nibble, screen color higher nibble, color from color RAM
-==== Sync with frame  ====
-Depending on the VIC type, there are 262/263 raster lines (NTSC) or 312 raster lines (PAL-B). Therefore, the VIC uses register at $D011 and the highest bit of register $D012 to represent the current raster line. Checking only the lower 8 bits and waiting for them to be 0 would therefore not work because this happens two times per frame. However, any number greater than 64 will only trigger once. Using a value of 255, we would sync to a rasterline at the end of the screen, well below the part where graphics are normally displayed:
-<syntaxhighlight lang="6502">
-        lda #$FF
-waitsync:
-        cmp $D012
-        bne waitsync
-</syntaxhighlight>
-As long as there have more than 63 cycles passed since the snyc, the next sync will happen at the next frame.
-This works fine as long as we don't miss the line 255 due to an interrupt. If your program has interrupts that are not synced to a rasterline, you can change the condition as follows
-<syntaxhighlight lang="6502">
-        lda #$E3
-waitsync:
-        cmp $D012
-        bcs waitsync
-</syntaxhighlight>
-Now we have a window between raster line $E4 and $FF to trigger our sync, which we will meet even if a standard Kernal interrupt comes in-between. Of course, our main program now has to burn around 1700 cycles to avoid a retriggering in the same frame.
-==== Getting something on screen ====
-Output a character:
-<syntaxhighlight lang="6502">
-        lda     #C       ;C must be the char code according to the PETSCII code table
-        jsr     $FFD2    ;you can also use the direct address $FC1A, function preserves A,X,Y and enables interrupt
-</syntaxhighlight>
-Since the [https://en.wikipedia.org/wiki/PETSCII#Character_set PETSCII code table] contains also control characters, this method can be also used to clear the screen, move the cursor or set the text color. However, some functions are shorter (and faster) by directly calling the respective KERNAL function:
-<syntaxhighlight lang="6502">
-Clear screen             JSR $E544
-Cursor home position     JSR $E566
-Output newline character JSR $AAD7
-Set text color           LDA #COLOR, STA $286
-Set border color         LDA #COLOR, STA $D020   ;not possible with a PETSCII control code
-Set background color     LDA #COLOR, STA $D021   ;not possible with a PETSCII control code
-</syntaxhighlight>
-Copy characters directly to screen memory:
-<syntaxhighlight lang="6502">
-.macpack cbm   ;scrcode macro
-SCREEN_BASE=$400
-LINE=5    ;for example
-COLUMN=10 ;for example
-        ldx     #endtext-text-1
-@loop:  lda     text,x
-        sta     SCREEN_BASE+LINE*40+COLUMN,x
-        dex
-        bpl     @loop
-text:   scrcode "hello world!"
-endtext:
-</syntaxhighlight>
-Note that the text needs to be stored in '''screen code''' format, not in PETSCII (see [https://sta.c64.org/cbm64pettoscr.html Commodore 64 PETSCII code to screen code conversion] for the differences). Furthermore, the example above only writes to the screen memory, not the color RAM, assuming that the color RAM already contains the intended text color. This is the case after issuing a clear screen on most C64 machines, except for some old ROM revisions. To be on the save side you would have to write to color RAM as well, which costs another 5 byte:
-<syntaxhighlight lang="6502">
-.macpack cbm     ;scrcode macro
-SCREEN_BASE=$400
-COLOR_RAM  =$D800
-LINE       =5    ;for example
-COLUMN     =10   ;for example
-COLOR      =1    ;white
-        ldx     #endtext-text-1
-@loop:  lda     text,x
-        sta     SCREEN_BASE+LINE*40+COLUMN,x
-        lda     #COLOR
-        sta     COLOR_RAM  +LINE*40+COLUMN,x
-        dex
-        bpl     @loop
-text:   scrcode "hello world!"
-endtext:
-</syntaxhighlight>
-=== Sound ===
-The Commodore 64 uses the famous SID chip to generate sound.
-To be added soon.
-==== Make some noise ====
-To be added soon.
-=== Useful Kernal functions ===
-==== Get a pseudo random number ====
-<syntaxhighlight lang="6502">
-        lda     #1
-        jsr     $E09A
-        lda     $63
-</syntaxhighlight>
-The sequence of random numbers is always the same after a cold start or reset, the first 20 numbers are:
-<syntaxhighlight lang="6502">
-,24,231,4,177,170,193,101,231,18,196,1,75,48,149,36,124,53,65,154
-</syntaxhighlight>
-==== Increment a zero page counter, return in X register, clear Y register ====
-This is part of the string handling function in the BASIC ROM, but the code could be useful for some loop stuff.
-<syntaxhighlight lang="6502">
-        jsr     $B5FF    ;does inc $23, ldx $23, ldy #$00, rts
-</syntaxhighlight>
-=== Additional Resources ===
-* Codebase 64 https://codebase64.org/doku.php?id=base:start
-* Commodore 64 Memory map https://sta.c64.org/cbm64mem.html
-* C64 BASIC & KERNAL ROM Disassembly https://www.pagetable.com/c64ref/c64disasm/
-== Apple II ==
-The Apple II is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak.
-=== Setting up ===
-* ACME 6502 cross-assembler(https://sourceforge.net/projects/acme-crossass/)
-* Apple Commander (http://applecommander.sourceforge.net) for batch compilation
-* AppleWin emulator (https://github.com/AppleWin/AppleWin/releases). Supports Mockingboard card(AY-8910+speech synthesier), HDD, Z80 card(for CP/M), mouse etc.
-* CiderPress(https://a2ciderpress.com)
-Compilation can be done as follows (master.dsk can be found with applewin)
-<syntaxhighlight>
-acme hl.asm
-java -jar AppleCommander-1.3.5.jar -d master.dsk hl
-java -jar AppleCommander-1.3.5.jar -p master.dsk hl B 24576 < hl.bin
-</syntaxhighlight>
-=== Memory Map ===
-<syntaxhighlight lang="6502">
--255	 $0-$FF     ZERO-PAGE SYSTEM STORAGE
--511      $100-$1FF    SYSTEM STACK
--767      $200-$2FF    KEYBOARD CHARACTER BUFFER
--975      $300-$3CF    OFTEN AVAILABLE AS FREE SPACE FOR USER PROGRAMS
--1023     $3D0-3FF     SYSTEM VECTORS
--2047     $400-$7FF    TEXT AND LO-RES GRAPHICS PAGE 1 <--- !!!
--LOMEM    $800-LOMEM   PROGRAM STORAGE
--3071     $800-$BFF    TEXT AND LO-RES GRAPHICS PAGE 2 OR FREE SPACE
--8191     $C00-$1FFF   FREE SPACE UNLESS RAM APPLESOFT IS IN USE
--16383   $2000-$3FFF   HI-RES PAGE 1 OR FREE SPACE <--- !!!
--24575   $4000-$5FFF   HI-RES PAGE 2 OR FREE SPACE
--38999   $6000-$95FF   FREE SPACE AND STRING STORAGE
--49151   $9600-$BFFF   DOS
--53247   $C000-$CFFF   I/O HARDWARE (RESERVED)
--57343   $D000-$DFFF   APPLESOFT IN LANGUAGE CARD OR ROM
--63487   $E000-$F7FF   APPLESOFT OR INTEGER BASIC IN LANGUAGE CARD OR ROM
--65535   $F800-$FFFF   SYSTEM MONITOR
-</syntaxhighlight>
-=== Display ===
-=== Graphics Modes ===
-: Text Mode 40x24, for Apple IIe available 80x25 - use PR#3 for switch mode, or hardware switch
-: LowRes 40x48, 16 colors: https://en.wikipedia.org/wiki/Apple_II_graphics
-: Hires mode 280x192,6 colors: https://www.xtof.info/blog/?p=768
-https://mrob.com/pub/xapple2/colors.html
-https://archive.org/details/HiRes_Color_Graphics_on_the_Apple_II_Computer_by_Wozniak
-However for sizecoding, you almost never want to do direct-access to graphics for Apple II in size-coding because the Apple II graphics modes are horrible.  The only fast way to do things is with large lookup tables.  To do hires you need to divide by 7 which as you can imagine is a bit difficult to do compactly on 6502. Double-hires is even crazier on top of that.  Deater did manage a color-bar style effect in double-hires in 128B but that was doing some crazy tricks with the firmware BASIC routines, definitely not direct-access.
-Lores and Hires can be mixed modes and full-graphics
-The screen structure is called memory holes(https://retrocomputing.stackexchange.com/questions/2534/what-are-the-screen-holes-in-apple-ii-graphics). The GBASCALC($F847) procedure is used to calculate the address of the horizontal line : IN:reg.A=Y, out : GBASL/GBASH($26/$27)=address. See also https://www.callapple.org/uncategorized/use-of-apple-ii-color-graphics-in-assembly-language/
-==== Getting something on screen ====
-Here is an example of a XOR texture, created by g0blinish
-<syntaxhighlight lang="6502">
- *=$6000
- !to "HL.bin", plain	; set output file and format
- !cpu 6502		; set processor type
-GBASL	=	$26
-GBASH	=	$27
-SETGR    =     $FB40 ; setup LoRes
-GBASCALC = $F847 ; calc Address
-CLRTEXT =  $C050 ;display graphics
-SETTEXT =  $C051 ;display text
-CLRMIXED = $C052 ;clear mixed mode- enable full graphics
-SETMIXED = $C053 ;enable graphics/text mixed mode
-PAGE1 =    $C054 ;select text/graphics page1
-PAGE2 =    $C055 ;select text/graphics page2
-CLRHIRES = $C056 ;select Lo-res
-SETHIRES = $C057 ;select Hi-res
-TMP= $FA
-	JSR   SETGR      ;GR
-	BIT CLRMIXED ; full screen
-	LDA #0 ; A=0
-	STA TMP ; POKE $FA,A
-YLP ;
-	LDA TMP ; A=PEEK($FA)
-;	LSR ; A=A/2
-	JSR GBASCALC
-	LDY #0;Y=0
-XLP TYA ; A=Y
-	EOR TMP ; A=A xor PEEK($FA)
-	and #$0F ; A=A and 15
-	TAX ; X=A
-	LDA COLORS,X ;A=PEEK(COLORS+X)
-	STA(GBASL),Y ; POKE PEEK($26)+256*PEEK($27)+Y,A
-	INY ; Y=Y+1
-	CPY #40 ; Y=40?
-	BNE XLP
-	INC TMP ; POKE $FA,PEEK($FA)+1
-	LDA TMP ; A=PEEK($FA)
-	CMP #24 ; A=24?
-	BNE YLP
-M1 JMP M1 ; replace to RTS
-COLORS ;N*17, pixel format is AAAABBBB, AAAA - upper dot, BBBB - lower dot
-!byte $00,$11,$22,$33,$44,$55,$66,$77
-!byte $88,$99,$AA,$BB,$CC,$DD,$EE,$FF
-</syntaxhighlight>
-==== Sound  ====
-Here is an example for using the speaker, based onthe following basic program:
-<syntaxhighlight lang="basic">
-; 50  POKE 768,V: POKE 769,P - 255 *  INT (P / 256): POKE 800,1 + P / 256
-; 60  CALL 770: RETURN
-; 95  FOR K = 1 TO N: READ V(K),P(K): NEXT K
-; 100  FOR K = 1 TO N:V = V(K):P = P(K)
-; 110  GOSUB 50
-;!byte 173,48,192,136,208,5,206,1,3,240,9,202,208,245,174,0,3,76,2,3,206,32,3,208,240,96
-</syntaxhighlight>
-<syntaxhighlight lang="6502">
- *=$6000
- !to "HL.bin", plain	; set output file and format
- !cpu 6502		; set processor type
-;start
-; 95  FOR K = 1 TO N: READ V(K),P(K): NEXT K
-; 100  FOR K = 1 TO N:V = V(K):P = P(K)
-ini:
-	lda #70
-	sta cnt+1
-	lda #music&255
-	sta gotbyte+1
-	lda #music/256
-	sta gotbyte+2
-lop:
-;V
-	jsr gotbyte
-	sta L300
-	jsr gotbyte
-;P
-	jsr gotbyte
-	sta L301
-	jsr gotbyte
-	clc
-	adc #1
-	sta L320
-	jsr beep
-	dec cnt+1
-cnt lda #70
-	bne lop
-; 110  GOSUB 50
-; 50  POKE 768,V: POKE 769,P - 255 *  INT (P / 256): POKE 800,1 + P / 256
-; 60  CALL 770: RETURN
-	jmp ini
-gotbyte
-	lda music
-	inc gotbyte+1
-	bne noinch
-	inc gotbyte+2
-noinch
-	rts
-;!byte 173,48,192,136,208,5,206,1,3,240,9,202,208,245,174,0,3,76,2,3,206,32,3,208,240,96
-beep:
-	ldy #1
-	ldx #1
-loc_302:
-		LDA	$C030
-loc_305:
-		DEY
-		BNE	loc_30D
-		DEC	L301
-loc_30B:
-		BEQ	loc_316
-loc_30D:
-		DEX
-		BNE	loc_305
-		LDX	L300
-		JMP	loc_302
-loc_316:
-		DEC	L320
-		BNE	loc_30B
-		RTS
-L301 !byte 0
-L300 !byte 0
-L320 !byte 0
-music
- !word 76,192,85,64,96,64,102,64,114,128,114,64,96,64,102,64,114,64,128,64
- !word 114,64,152,64,171,64,152,512,76,192,85,64,96,64,102,64,114,128,114,64
- !word 96,64,102,64,114,64,128,64,114,64,152,64,171,64,152,512,85,64,85,64
- !word 85,64,96,64,144,128,144,64,128,64,76,128,85,64,96,64,144,128,114,64
- !word 96,64,102,128,114,64,128,64,128,128,114,64,128,64,114,512,85,64,85,64
- !word 85,64,96,64,144,128,144,64,128,64,76,128,85,64,96,64,144,128,114,64
- !word 96,64,102,128,114,64,128,64,128,64,128,128,96,64,85,64,96,64,102,64,114,64,114,64
-</syntaxhighlight>
-=== Additional Resources ===
-* Deater's page on Apple II sizecoding http://www.deater.net/weave/vmwprod/demos/sizecoding.html
-* Article on double hi-res http://www.battlestations.zone/2017/04/apple-ii-double-hi-res-from-ground-up.html
-* Applesoft Hi-Res Subroutines : http://hackzapple.org/scripts_php/index.php?menu=5&mod=ASM&sub=AAL&sub2=8112&PHPSESSID=f65fabfd0cdbf56b6bdc0ddac25117c6#a2
-== Atari Lynx ==
-The Atari Lynx consists of the 6502 with custom hardware for graphics and sound.
-=== Setting up ===
-Setting up your development platform for the Atari Lynx:
-* Assembler: -
-* Emulator(s): -
-=== Video display ===
-To be added soon.
-==== Getting something on screen ====
-To be added soon.
-=== Sound ===
-To be added soon.
-==== Make some noise ====
-To be added soon.
-=== Additional Resources ===
-Sizecoding resource for the Atari Lynx are sparse
-* 42Bastian's website (link to be added)