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leftshift.asm
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leftshift.asm
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*=$0801
BYTE $0E,$08,$0A,$00,$9E,$20,$28,$32,$30,$36,$34,$29,$00,$00,$00
; [CODE START] ----------------------------------------------------------------
*=$0810
Const_StartLine = $7c0
;http://dustlayer.com/vic-ii/2013/4/23/vic-ii-for-beginners-part-2-to-have-or-to-not-have-character
; ***********************************************************************************
; Step 1 Redefine char set
; ***********************************************************************************
Character_Set
sei ; disable interrupts while we copy
ldx #$08 ; we loop 8 times (8x255 = 2Kb)
lda #$33 ; make the CPU see the Character Generator ROM...
sta $01 ; ...at $D000 by storing %00110011 into location $01
lda #$d0 ; load high byte of $D000
sta $fc ; store it in a free location we use as vector
LDA #$30 ;
STA $fe ;
LDA #0 ;
STA $fd
ldy #$00 ; init counter with 0
sty $fb ; store it as low byte in the $FB/$FC vector
loop lda ($fb),y ; read byte from vector stored in $fb/$fc
sta ($fd),y ; write to the RAM under ROM at same position
iny ; do this 255 times...
bne loop ; ..for low byte $00 to $FF
inc $fc ; when we passed $FF increase high byte...
inc $fe
dex ; ... and decrease X by one before restart
bne loop ; We repeat this until X becomes Zero
lda #$37 ; switch in I/O mapped registers again...
sta $01 ; ... with %00110111 so CPU can see them
cli ; turn off interrupt disable flag
LDA #28
STA $d018 ;
; ***********************************************************************************
; Step 2 - Initialize the redefined characters in charset used for scrolling, they
; start at index charset index 64 which equate to 64*8 = $200 + $3000=$3200
; ***********************************************************************************
ldy #$00
@inner lda #0
sta $3200,y
iny
cpy #255
bne @inner
ldy #00
@inner2 sta $32ff,y
iny
cpy #66
bne @inner2
; ***********************************************************************************
; Step 3 - put redefined characters on a row on the screen
; ***********************************************************************************
ldy #0
ldx #64 ; character set offset
@loop1 txa
sta Const_StartLine,y
iny
inx
cpy #40
bne @loop1
; ***********************************************************************************
; Step 4 - MAIN PROGRAM LOOP - start the shifting
; ***********************************************************************************
ldx #0
@keepgoing
lda newmessage,x
beq @done
jsr grab_next_char
stx xsave
jsr shiftchar
jsr shiftchar
jsr shiftchar
jsr shiftchar
jsr shiftchar
jsr shiftchar
jsr shiftchar
jsr shiftchar
ldx xsave
inx
jmp @keepgoing
@done rts
; ***********************************************************************************
; Subroutines Grab next char
; ***********************************************************************************
grab_next_char
tay
lda charhi,y
sbc #2
sta $fc
lda charlow,y
sta $fb
ldy #40
lda charhi,y
sta $fe
lda charlow,y
sta $fd
ldy #0
@inner lda ($fb),y
sta ($fd),y
iny
cpy #8
bne @inner
@end_loop rts
; ***********************************************************************************
; Subroutine Shift char
; ***********************************************************************************
shiftchar
jsr Smooth_Scroll
ldx #00
@loop
txa
tay
lda charhi,y
sta $fc
lda charlow,y
sta $fb
iny
lda charhi,y
sta $fe
lda charlow,y
sta $fd
ldy #7
@loopab
lda ($fd),y
and #%10000000
bne @sec
@clc clc
jmp @cont
@sec sec
@cont lda ($fb),y
rol
sta ($fb),y
dey
cpy #$ff
bne @loopab
inx
bne @keepgoing
@keepgoing cpx #41
bne @loop
rts
; ***********************************************************************************
; Subroutine Smooth_Scroll
; ***********************************************************************************
Smooth_Scroll
;@w1 bit $d011 ; Wait for Raster to be off screen
; bpl @w1
;@w2 bit $d011
; bmi @w2
@loop
lda $D012
cmp #100
bcc @loop
rts
xsave byte 00
newmessage null 'hello this is a message from gray defender this is my message will it repeat it might! '
charlow byte $00,$08,$10,$18,$20,$28,$30,$38,$40,$48,$50,$58,$60,$68,$70,$78,$80,$88,$90,$98,$a0,$a8,$b0,$b8,$c0,$c8,$d0,$d8,$e0,$e8,$f0,$f8,$00,$08,$10,$18,$20,$28,$30,$38,$40,$48
charhi byte $32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$32,$33,$33,$33,$33,$33,$33,$33,$33,$33,$33