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+==== Duo Blast =====
+You will need to use sprite pad to draw 3 sprites. Actually, just draw two triangles. One that points up and another that points down. Finally draw a small square or a dot then save the lot. Now try this Acme Cross Assembler routine.
+=== source ===
+Creating your first game
+<code>
+;This is an example tutorial for you to
+;learn how to create your own 2 player
+;Shot 'em Up, which includes joystick
+;control, a score system, etc.
+;Let's setup the perameters for our
+;game. These are the player positions.
+plr1_x   = $0340 ;Player 1 x-position
+plr1_y   = $0341 ;Player 1 y-position
+plr2_x   = $0342 ;Player 2 x-position
+plr2_y   = $0343 ;Player 2 y-position
+;Our parameters for the player bullets
+plr1b_x  = $0344 ;Player 1 bullet-xpos
+plr1b_y  = $0345 ;Player 1 bullet-ypos
+plr2b_x  = $0346 ;Player 2 bullet-xpos
+plr2b_y  = $0347 ;Player 2 bullet-ypos
+;Collisions parameters
+plr1col  = $0350 ;Value storage for p1
+plr2col  = $0354 ;Value storage for p2
+;bullet lockup routines
+plr1lockup = $0360 ;Lockup for players
+plr2lockup = $0361 ;shooting
+;We need to create a jump start for this
+;example, so we will create our own jump
+;address where it does not overlap data
+;which had been loaded.
+         !to "duoblast.prg",cbm
+         *= $1000-2
+         !binary "music.dat"
+         *= $2000-2
+         !binary "sprites.dat"
+         *= $2400
+start      sei ;Set irq flag
+;Clear the screen without JSR $E544
+         ldx #$00    ;Calls a routine
+clear    lda #$20    ;to fill the whole
+         sta $0400,x ;screen with #$20,
+         sta $0500,x ;which is the
+         sta $0600,x ;blank space
+         sta $06e8,x ;routine.
+         inx         ;
+         bne clear   ;
+;You should be familiar with the next
+;example code. If not then look at the
+;earlier chapters of A$$EMBLE IT!
+         lda #$00
+         sta $d020
+         sta $d021
+         lda #$16
+         sta $d018
+         lda #$1b
+         sta $d011
+         lda #$ff
+         sta $d015
+;Now here we create the sprite objects
+         lda #$81
+         sta $07f8 ;Player 1 ship
+         lda #$82
+         sta $07f9 ;Player 1 bullet
+         lda #$80
+         sta $07fa ;Player 2 ship
+         lda #$82
+         sta $07fb ;Player 2 bullet
+;This is where we setup the colours of
+;the two players and bullets.
+         lda #$02  ;Colour red
+         sta $d027 ;Player 1
+         sta $d028 ;Player 1 bullet
+         lda #$07  ;Colour yellow
+         sta $d029 ;Player 2
+         sta $d02a ;Player 2 bullet
+;This is a different routine, as now the
+;default sprite positions are copied to
+;the declared parameters.
+         lda $d000   ;This is a method
+         sta plr1_x  ;of copying and
+         lda $d001   ;pasting the sprite
+         sta plr1_y  ;positions so that
+         lda $d002   ;you can use this
+         sta plr1b_x ;to program the
+         lda $d003   ;sprites positions
+         sta plr1b_y ;later on in the
+         lda $d004   ;routines, for a
+         sta plr2_x  ;much faster
+         lda $d005   ;and decent
+         sta plr2_y  ;movement for all
+         lda $d006   ;the sprites in
+         sta plr2b_x ;this game.
+         lda $d007
+         sta plr2b_y
+;Now we reposition the two players and
+;put the bullets into zero
+         lda #$42    ;All this is the
+         sta plr1_y  ;repositioning the
+         lda #$18    ;two player ships,
+         sta plr1_x  ;by using the 'x'
+         lda #$e0    ;positions and the
+         sta plr2_y  ;'y' positions,
+         lda #$98    ;as simple as that
+         sta plr2_x  ;:)
+         lda #$00    ;All bullets are
+         sta plr1b_x ;repositioned to
+         sta plr1b_y ;the zero value
+         sta plr2b_x ;yet again 'x' and
+         sta plr2b_y ;'y' positions
+;Setup the scoreboard
+         lda #$30  ;We put zero on:
+         sta $0400 ;first line
+         lda #$02  ;paint first line
+         sta $d800 ;red
+         lda #$30  ;zero put on
+         sta $0427 ;first line as last
+         lda #$07  ;paint character
+         sta $d827 ;yellow
+;Now for the main body of this program
+;the Interrupt flag, but we wont use
+;JMP $EA81 or JMP $EA31, as no keyboard
+;control will be required
+         lda #<int ; Call INT values
+         ldx #>int ; into an IRQ raster
+         ldy #$00  ; interrupt value and
+         sta $0314 ; zero the rasterline
+         stx $0315 ;
+         sty $d012
+         lda #$7f  ; Keep the screen on
+         ldx #$1b  ; and continue the
+         sta $dc0d ; main interrupt
+         stx $d011 ; read
+         lda #$00  ;Initialise music
+         tax       ;according to tune
+         tay       ;number
+         jsr $1000 ;
+         lda #$01
+         sta $d019 ;IRQ is turned on
+         sta $d01a ;----------------
+         lda $dc0d ;Copy $DC0D to $DD0D
+         sta $dd0d ;to have the IRQ
+                   ;working properly.
+         cli       ;Clear IRQ flag
+loop     jmp loop  ;Jump to the loop
+;Our main interrupt
+int      asl $d019 ;Keep $D019 running
+;Call routine to expand and reconvert
+;the sprite positions
+         jsr expand
+;Call routine to read joystick port 2
+;for player 1 and player 2
+         jsr read1up
+         jsr read2up
+;Call routine for bullet movements
+         jsr bullmove
+;Call routine for collision detection
+;and player 1 and player 2 bullet to
+;player collision.
+         jsr detect
+         jsr p1col
+         jsr p2col
+;And finally play the music
+         jsr $1003 ;Play music
+         pla ; An IRQ loop routine.
+         tay ;
+         pla ; This will keep all the
+         tax ; jsr routines playing
+         pla ; without using JMP $EA81
+         rti ; or JMP $EA31
+;Expand and reconver the sprite position
+expand   lda plr1_y   ;Copy player y
+         sta $d001    ;to exact position
+         lda plr1b_y  ;Copy bullet 1 y
+         sta $d003    ;to exact position
+         lda plr2_y   ;The same goes
+         sta $d005    ;with this routine
+         lda plr2b_y  ;but instead it
+         sta $d007    ;works with p2.
+         lda plr1_x   ;Copy player x
+         asl a        ;calculate 64
+         ror $d010    ;Expand x pos.
+         sta $d000    ;put at exact xpos
+         lda plr1b_x  ;Copy bullet
+         asl a        ;and do the same
+         ror $d010    ;as with the
+         sta $d002    ;player.
+         lda plr2_x   ;
+         asl a        ;All this is the
+         ror $d010    ;same except that
+         sta $d004    ;it will work with
+         lda plr2b_x  ;Player 2 and the
+         asl a        ;Player 2 bullet
+         ror $d010    ;instead.
+         sta $d006    ;
+         rts          ;
+;Read joystick control for player1
+read1up  lda $dc00 ;Read port 2
+         lsr a ;Joystick up
+         lsr a ;Joystick down
+left1    lsr a ;Joystick left
+         bcs right1
+         ldx plr1_x ;Move player 1
+         dex        ;left across screen
+         dex        ;using 2 for speed
+         cpx #$0e   ;does the player
+         bcs set1   ;move further than
+         ldx #$0e   ;$0e, if so then
+set1     stx plr1_x ;stop. Else continue
+right1   lsr a      ;Joystick right
+         bcs fire1
+         ldx plr1_x ;Move player 1
+         inx        ;right across screen
+         inx        ;using the same
+         cpx #$9a   ;speed. If player
+         bcc set2   ;exceeds $9a, then
+         ldx #$9a   ;make the player
+set2     stx plr1_x ;stop.
+fire1    lsr a ;Firebutton
+         bcs nojoy1
+         lda plr1lockup ;Is player fire
+         cmp #$00       ;control
+         bne nojoy1     ;unlocked. If so
+         lda #$01       ;then lock fire
+         sta plr1lockup ;and position
+         ldx plr1_x     ;the bullet x
+         stx plr1b_x    ;and y positions
+         ldx plr1_y     ;exactly at the
+         stx plr1b_y    ;same areas as
+                        ;the player.
+nojoy1   rts
+;Read joystick control for Player 2
+;(joystick port 1)
+read2up  lda $dc01    ;Read JOY Port 1
+         lsr a ;up
+         lsr a ;down  ;Please read the
+left2    lsr a ;left  ;player 1
+         bcs right2   ;joystick control
+         ldx plr2_x   ;as this routine
+         dex          ;is exactly the
+         dex          ;same as the
+         cpx #$0e     ;player 1 controls
+         bcs set1_1   ;but works for
+         ldx #$0e     ;player 2.
+set1_1   stx plr2_x
+right2   lsr a
+         bcs fire2
+         ldx plr2_x
+         inx
+         inx
+         cpx #$9a
+         bcc set1_2
+         ldx #$9a
+set1_2   stx plr2_x
+fire2    lsr a
+         bcs nojoy2
+         lda plr2lockup
+         cmp #$00
+         bne nojoy2
+         lda #$01
+         sta plr2lockup
+         ldx plr2_x
+         stx plr2b_x
+         ldx plr2_y
+         stx plr2b_y
+nojoy2   rts
+;call bullet routines
+bullmove ldx plr1b_y  ;The bullet moves
+         inx          ;but if it hits
+         inx          ;$F6+ it will stop
+         inx          ;off screen else
+         inx          ;if below that
+         inx          ;limit, the bullet
+         inx          ;/ moves on, else
+         cpx #$f6     ;bullet off screen
+         bcc repsbul1
+         lda #$00       ;Turn off the
+         sta plr1lockup ;fire lockup
+         ldx #$f6
+repsbul1 stx plr1b_y
+         ldx plr2b_y  ;The bullet moves
+         dex          ;up but if it hits
+         dex          ;$0C- it will stop
+         dex          ;off screen, else
+         dex          ;if below that
+         dex          ;limit, the bullet
+         dex          ;/ moves on. else
+         cpx #$06     ;bullet off screen
+         bcs repsbul2
+         lda #$00       ;Turn off the
+         sta plr2lockup ;fire lockup
+         ldx #$06
+repsbul2 stx plr2b_y
+         rts
+;Setup collision detection for player 1
+;and player 2
+detect   lda plr1_x       ;Calculate
+         sec              ;the storage
+         sbc #$06         ;values for
+         sta plr1col+$00  ;the exact
+         clc              ;positions of
+         adc #$0c         ;player 1, so
+         sta plr1col+$01  ;that when the
+         lda plr1_y       ;opponents'
+         sec              ;bullet hits
+         sbc #$0c         ;the player,
+         sta plr1col+$02  ;it has to be
+         clc              ;in the exact
+         adc #$18         ;position of
+         sta plr1col+$03  ;player 1.
+         lda plr2_x       ;The same
+         sec              ;calculations
+         sbc #$06         ;for player 2
+         sta plr2col+$00  ;bullet to
+         clc              ;player
+         adc #$0c         ;collision.
+         sta plr2col+$01
+         lda plr2_y
+         sec
+         sbc #$0c
+         sta plr2col+$02
+         clc
+         adc #$18
+         sta plr2col+$03
+         rts
+;Check player 1 bullet collision on
+;player 2 ship
+p2col    lda plr1b_x     ;Is the bullet
+         cmp plr2col+$00 ;at the correct
+         bcc missp2      ;position where
+         cmp plr2col+$01 ;the player is?
+         bcs missp2      ;
+         lda plr1b_y     ;If not then
+         cmp plr2col+$02 ;the bullet
+         bcc missp2      ;misses the
+         cmp plr2col+$03 ;player.
+         bcs missp2      ;
+         lda #$f6        ;Else move
+         sta plr1b_y     ;bullet off
+         lda #$00        ;screen, turn
+         sta plr1lockup  ;off fire lock
+         inc $0400       ;add 1 point
+         lda $0400       ;check score
+         cmp #$3a        ;is it over 9?
+         bne missp2      ;if not then
+                         ;miss, else
+         jmp victory1    ;jump to win
+missp2   rts
+;Check player2 bullet on player 1 ship
+p1col    lda plr2b_x     ;Does the
+         cmp plr1col+$00 ;bullet hit
+         bcc missp1      ;the player in
+         cmp plr1col+$01 ;exact position
+         bcs missp1      ;of the player
+         lda plr2b_y     ;ship? If so
+         cmp plr1col+$02 ;then continue
+         bcc missp1      ;else jump to
+         cmp plr1col+$03 ;missp1
+         bcs missp1
+         lda #$06
+         sta plr2b_y
+         lda #$00
+         sta plr2lockup
+         inc $0427       ;Add 1 point
+         lda $0427       ;check score
+         cmp #$3a        ;is it over '9'
+         bne missp1      ;if so then
+         jmp victory2    ;player2 wins
+missp1   rts
+victory1 sei             ;Stop all IRQs
+         lda #$00        ;Turn off all
+         sta $d015       ;the sprites
+         ldx #$00        ;Call a routine
+win1     lda vic1,x      ;to display
+         sta $0400,x     ;player1 wins
+         lda #$01        ;message and
+         sta $d800,x     ;paint the
+         inx             ;message white
+         cpx #$28        ;and display
+         bne win1        ;as 40 chars
+         jmp space       ;Jump to space
+                         ;prompt
+victory2 sei             ;   Look at
+         lda #$00        ;  'victory1'
+         sta $d015       ;same function
+         ldx #$00        ;This routine
+win2     lda vic2,x      ;does exactly
+         sta $0400,x     ;the same, but
+         lda #$01        ;it reads the
+         sta $d800,x     ;text from
+         inx             ;vic2 so that
+         cpx #$28        ;player 2 wins
+         bne win2        ;the game
+         jmp space       ;You know this
+                         ;if not then
+                         ;look at the
+                         ;previous
+                         ;'jmp space'
+                         ;prompt
+space    ldx #$00        ;Another text
+setspc   lda spc,x       ;display
+         sta $07c0,x     ;routine. This
+         lda #$03        ;time position
+         sta $dbc0,x     ;the text at
+         inx             ;the bottom of
+         cpx #$28        ;the screen as
+         bne setspc      ;40 chars
+;Lame hit space routine :)
+hitspace lda #$80        ;Create a
+raster   cmp $d012       ;raster control
+         bne raster      ;to continue
+         jsr $1003       ;playing music
+         lda $dc01       ;Read SPACEBAR
+         cmp #$ef        ;if not pressed
+         bne raster      ;then jump to
+                         ;the raster to
+                         ;continue
+                         ;the SPACE read
+                         ;routine and
+                         ;play music
+         jmp start       ;Restart game
+;Our text display data tables.
+         ;Player 1 victory
+vic1     !scr "player 1 proves that"
+         !scr " player 2 is a loser"
+         ;Player 2 victory
+vic2     !scr "player 2 proves that"
+         !scr " player 1 is a loser"
+         ;Spacebar prompt message
+spc      !scr "  press the spacebar"
+         !scr " for another game!  "
+</code>