2021-04-20 20:30:05 +00:00
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CH = $24
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CV = $25
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2021-04-21 04:35:48 +00:00
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BASL = $28
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BASH = $29
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SEEDL = $4E
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2021-04-20 20:30:05 +00:00
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2021-04-21 04:35:48 +00:00
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DRAW_PAGE = $FF
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PAGE0 = $C054
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2021-04-20 20:30:05 +00:00
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HGR = $F3E2
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SETTXT = $FB39
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TABV = $FB5B ; store A in CV and call MON_VTAB
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STORADV = $FBF0 ; store A at (BASL),CH, advancing CH, trash Y
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MON_VTAB = $FC22 ; VTAB to CV
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VTABZ = $FC24 ; VTAB to value in A
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HOME = $FC58
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2021-04-21 04:35:48 +00:00
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WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us
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2021-04-20 20:30:05 +00:00
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COUT = $FDED
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COUT1 = $FDF0
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COUTZ = $FDF6 ; cout but ignore inverse flag
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ypos = $2000
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xpos = $2100
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move:
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jsr HGR
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2021-04-21 04:35:48 +00:00
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sta DRAW_PAGE
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2021-04-20 20:30:05 +00:00
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jsr SETTXT
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next_frame:
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ldx #0
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next_text:
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lda xpos,X
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bne not_new
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new_text:
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2021-04-21 04:35:48 +00:00
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jsr random8
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and #$1f
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adc #$4
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2021-04-20 20:30:05 +00:00
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sta xpos,X
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2021-04-21 04:35:48 +00:00
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jsr random8
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and #$f
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2021-04-20 20:30:05 +00:00
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sta ypos,X
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not_new:
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lda xpos,X
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sta CH
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lda ypos,X
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sta CV
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jsr MON_VTAB
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2021-04-21 04:35:48 +00:00
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lda BASH
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clc
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adc DRAW_PAGE
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sta BASH
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2021-04-20 20:30:05 +00:00
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txa
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pha
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ldx #0
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2021-04-21 04:35:48 +00:00
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print_loop:
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2021-04-20 20:30:05 +00:00
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lda text,X
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2021-04-21 04:35:48 +00:00
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php
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2021-04-20 20:30:05 +00:00
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ora #$80
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jsr STORADV
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inx
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2021-04-21 04:35:48 +00:00
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plp
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bpl print_loop
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2021-04-20 20:30:05 +00:00
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big_done:
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pla
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tax
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dec xpos,X
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inx
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cpx #20
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bne next_text
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2021-04-21 04:35:48 +00:00
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flip_pages:
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ldx #0
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lda DRAW_PAGE
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beq done_page
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inx
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done_page:
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ldy PAGE0,X ; set display page to PAGE1 or PAGE2
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eor #$4 ; flip draw page between $400/$800
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sta DRAW_PAGE
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clc
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adc #$4
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sta BASH
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lda #$0
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sta BASL
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clear_screen_outer:
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ldy #$f8
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clear_screen_inner:
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lda #$A0 ; space char
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sta (BASL),Y ; 100 101 110 111
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dey
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cpy #$FF
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bne clear_screen_inner
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inc BASH
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lda BASH
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and #$3
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bne clear_screen_outer
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lda #$50
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jsr WAIT
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2021-04-20 20:30:05 +00:00
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jmp next_frame
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2021-04-21 04:35:48 +00:00
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;=============================
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; random8
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;=============================
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; 8-bit 6502 Random Number Generator
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; Linear feedback shift register PRNG by White Flame
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; http://codebase64.org/doku.php?id=base:small_fast_8-bit_prng
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random8:
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lda SEEDL ; 2
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beq doEor ; 2
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asl ; 1
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beq noEor ; if the input was $80, skip the EOR ; 2
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bcc noEor ; 2
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doEor: eor #$1d ; 2
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noEor: sta SEEDL ; 2
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rts
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2021-04-20 20:30:05 +00:00
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text:
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.byte "HELL",'O'|$80
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