Difference between revisions of "Atari 8Bit"

Latest revision as of 16:32, 28 March 2024

Atari 8-bit family

The systems in this family are: Atari 400, 800, 5200, 1200XL, 600XL, 800XL, 130XE, 65XE, 800XE and XEGS.

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 can create atari XEX files out of the box. Download it at https://mads.atari8.info/
Emulator(s): I Found Altirra to work best for my usecases. 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:

Graphics Modes

The Atari 8-bit has many different video modes to take advantage of, here is an overview.

; mode ANTIC width  height colors DL     screen_mem
;  3    8    40     24     4      $be50  $be70
;  4    9    80     48     2      $bd48  $bd80
;  5   10    80     48     4      $bb68  $bba0
;  6   11    160    96     2      $b778  $b7e0
;  7   13    160    96     4      $af98  $b060
;  8   15    320   192     2      $a036  $a150,$b000
;  9   15    80    192     16*    $a036  $a150,$b000
; 10   15    80    192     9 *    $a036  $a150,$b000
; 11   15    80    192     16*    $a036  $a150,$b000
; 14   12    160   192     2      $af38  $b060
; 15   14    160   192     4      $a036  $a150,$b000
;
; * GTIA modes 
;  9: 4-bit pixel luminance only
; 11: 4-bit pixel color only
; 10: 9 colors set in location 704..712

Sync with frame

      lda 20
waitframe:
      cmp 20
      beq waitframe

Or a shorter version if you don't mind trashing RTCLOK (20)

waitframe
      lsr 20
      bcc waitframe

ROM-Routines

The atari 8-bit has various slow ROM routines to draw pixels and lines. Here is an example that draws an XOR pattern in graphics 7 mode using ROM calls:

To be added

Direct-to-screen textmodes

Fill screen with charset, (88,89)=address

 org $600; free 6th page:600-6ff
 ldy #0
fill: 
 tya
 sta(88),y
 iny
 bne fill
 jmp *

Player-Missile Sprites

The atari 8-bit has access to 4(+1) customisable player sprites and/or 4 missile sprites. Here is some example code that shows you how to use them.

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
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 sinewave+$c0,x
			sta sinewave+$80,y
			eor #$7f
			sta sinewave+$40,x
			sta sinewave+$00,y
 
			lda delta_lo+1
			adc #8
			sta delta_lo+1
			bcc nothing
			inc delta_hi+1
nothing
			inx
			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

Sound

The Atari 8-bit use the POKEY chip to generate sound.

https://en.wikipedia.org/wiki/POKEY

Make some noise

; from Analog, 1985-09,pp.25-32
*=$2000
AUDF1=$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 *

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/

Difference between revisions of "Atari 8Bit"

Latest revision as of 16:32, 28 March 2024

Contents

Atari 8-bit family

Setting up

Special Memory Adresses

Video display

Graphics Modes

Sync with frame

ROM-Routines

Direct-to-screen textmodes

Player-Missile Sprites

Sound

Make some noise

Additional Resources

Navigation menu

Personal tools

Namespaces

Variants

Views

More

Search

Navigation

Tools

@@ Line 7: / Line 7: @@
 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/
+* Assembler: MADS Assembler - This assembler can create atari XEX files out of the box. 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.
+* Emulator(s): I Found Altirra to work best for my usecases. Make sure to use the original Rev2 rom for best compatibility.
 ==== Special Memory Adresses ====
@@ Line 18: / Line 18: @@
 * https://en.wikipedia.org/wiki/ANTIC
 * https://www.atariarchives.org/agagd/chapter1.php
+==== Graphics Modes ====
+The Atari 8-bit has many different video modes to take advantage of, here is an overview.
+<syntaxhighlight lang="6502">
+; mode ANTIC width  height colors DL     screen_mem
+;  3    8    40     24     4      $be50  $be70
+;  4    9    80     48     2      $bd48  $bd80
+;  5   10    80     48     4      $bb68  $bba0
+;  6   11    160    96     2      $b778  $b7e0
+;  7   13    160    96     4      $af98  $b060
+;  8   15    320   192     2      $a036  $a150,$b000
+;  9   15    80    192     16*    $a036  $a150,$b000
+; 10   15    80    192     9 *    $a036  $a150,$b000
+; 11   15    80    192     16*    $a036  $a150,$b000
+; 14   12    160   192     2      $af38  $b060
+; 15   14    160   192     4      $a036  $a150,$b000
+;
+; * GTIA modes
+;  9: 4-bit pixel luminance only
+; 11: 4-bit pixel color only
+; 10: 9 colors set in location 704..712
+</syntaxhighlight>
 ==== Sync with frame  ====
 <syntaxhighlight lang="6502">
-RTCLOK      equ $0012
+       lda 20
-       lda RTCLOK+2
+waitframe:
-waits
+       cmp 20
-       cmp RTCLOK+2
+       beq waitframe
-       beq waits
 </syntaxhighlight>
-Or if you don't mind trashing RTCLOK
+Or a shorter version if you don't mind trashing RTCLOK (20)
+<syntaxhighlight lang="6502">
+waitframe
+      lsr 20
+      bcc waitframe
+</syntaxhighlight>
+==== ROM-Routines ====
+The atari 8-bit has various slow ROM routines to draw pixels and lines. Here is an example that draws an XOR pattern in graphics 7 mode using ROM calls:
 <syntaxhighlight lang="6502">
-RTCLOK      equ $0012
+To be added
-waits
-      lsr RTCLOK+2
-      bcc waits
 </syntaxhighlight>
-Which is two bytes shorter.
+==== Direct-to-screen textmodes ====
+Fill screen with charset, (88,89)=address
-==== 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
+fill:
+ tya
   sta(88),y
   iny
-  bne fl
+  bne fill
   jmp *
 </syntaxhighlight>
-To be added soon.
+==== Player-Missile Sprites ====
+The atari 8-bit has access to 4(+1) customisable player sprites and/or 4 missile sprites.
+Here is some example code that shows you how to use them.
 <syntaxhighlight lang="6502">
@@ Line 144: / Line 172: @@
 * https://en.wikipedia.org/wiki/POKEY
-==== BASIC ====
+==== Make some noise ====
 <syntaxhighlight lang="6502">
 ; from Analog, 1985-09,pp.25-32
@@ Line 169: / Line 198: @@
   jmp *
 </syntaxhighlight>
-==== Make some noise ====
-To be added soon.
 === Additional Resources ===