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base:1x1_upscroll [2021-06-11 15:32] (current)
richard created
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 +===== 1x1 Upscroll - the basics =====
 +Making 1x1 horizontal scrolls are quite easy enough, but what about making a 1x1 upscroll text. First, a Y-Position delay pointer has to be made in order to ensure the scroll does not scroll too fast. Then you create a Y position pointer that controls the smoothness of the VIC2 vertical screen position (Once stored into the raster). The char rows have to be moved up 1 row, before updating the message in place to display the text.
 +This example is a full text upscroll routine ...
 +;Upward scroll with raster IRQ by Richard/TND
 +row = $0400
 +!to "upwardscroll.prg",cbm
 +* = $0801
 +!basic 2064
 +* = $0810 
 +;Reset scroll text
 +lda #<scrollText 
 +sta messRead+1
 +lda #>scrollText 
 +sta messRead+2
 +;Kernal clear and fill screen with crsr white
 +lda #$05
 +jsr $ffd2
 +jsr $e544
 +lda #$00
 +sta $d020
 +sta $d021
 +;Prepare interrupts
 +ldx #<irq
 +ldy #>irq
 +lda #$7f
 +stx $314
 +sty $315
 +sta $dc0d
 +sta $dd0d
 +lda #$2a
 +sta $d012
 +lda #$1b
 +sta $d011
 +lda #$01
 +sta $d019
 +sta $d01a
 +jmp mainLoop
 +;IRQ 1 - Mask out the top+bottom row for upscroll appearance
 +;and generate raster timer (RT), which can be synced with
 +inc $d019
 +lda #$32
 +sta $d012
 +lda #$70 
 +sta $d011
 +lda #1
 +sta rt
 +ldx #<irq2
 +ldy #>irq2
 +stx $0314
 +sty $0315
 +jmp $ea7e
 +;IRQ 2 smooth scroller     
 +inc $d019
 +lda #$f2 
 +sta $d012
 +lda ypos
 +ora #$10
 +sta $d011
 +ldx #<irq
 +ldy #>irq
 +stx $0314
 +sty $0315
 +jmp $ea7e
 +;Main loop for controlling my demonstration
 +lda #0
 +sta rt
 +cmp rt
 +beq *-3
 +jsr upScroll
 +jmp mainLoop
 +;Upscroll routine 
 +upScroll lda ydelay ;Control delay
 +cmp #3
 +beq loop01
 +inc ydelay
 +loop01 lda #0
 +sta ydelay
 +lda ypos
 +sbc #1
 +and #7
 +sta ypos ;This will store YPOS, but in your IRQ you will need to add ORA #$10 
 +bcs skipScroll
 +ldx #$27 ;Shift rows (first half)
 +lda row+(1*40),x
 +sta row,x
 +lda row+(2*40),x
 +sta row+(1*40),x
 +lda row+(3*40),x
 +sta row+(2*40),x
 +lda row+(4*40),x
 +sta row+(3*40),x
 +lda row+(5*40),x
 +sta row+(4*40),x
 +lda row+(6*40),x
 +sta row+(5*40),x
 +lda row+(7*40),x
 +sta row+(6*40),x
 +lda row+(8*40),x
 +sta row+(7*40),x
 +lda row+(9*40),x
 +sta row+(8*40),x
 +lda row+(10*40),x
 +sta row+(9*40),x
 +lda row+(11*40),x
 +sta row+(10*40),x
 +lda row+(12*40),x
 +sta row+(11*40),x
 +bpl shiftRows1
 +ldx #$27  ;Shift rows (second half)
 +lda row+(13*40),x
 +sta row+(12*40),x
 +lda row+(14*40),x
 +sta row+(13*40),x
 +lda row+(15*40),x
 +sta row+(14*40),x
 +lda row+(16*40),x
 +sta row+(15*40),x
 +lda row+(17*40),x
 +sta row+(16*40),x
 +lda row+(18*40),x
 +sta row+(17*40),x
 +lda row+(19*40),x
 +sta row+(18*40),x
 +lda row+(20*40),x
 +sta row+(19*40),x
 +lda row+(21*40),x
 +sta row+(20*40),x
 +lda row+(22*40),x
 +sta row+(21*40),x
 +lda row+(23*40),x
 +sta row+(22*40),x
 +lda row+(24*40),x
 +sta row+(23*40),x
 +bpl shiftRows2
 +;Now input message
 +ldx #$00
 +lda scrollText,x
 +cmp #$00
 +bne storeText 
 +lda #<scrollText
 +sta messRead+1
 +lda #>scrollText
 +sta messRead+2
 +jmp messRead
 +;Store the row of text from the scroll text
 +sta row+(24*40),x
 +cpx #$28
 +bne messRead
 +;Fetch next row of text from the scroll text
 +lda messRead+1
 +adc #40 ;Read 40 chars for next row
 +sta messRead+1
 +;bcs exitUpScroll
 +lda messRead+2
 +adc #$00
 +sta messRead+2
 +ydelay !byte 0
 +ypos !byte 0
 +rt !byte 0
 +;Our main scroll text message 
 +!ct scr
 +!text "----------------------------------------"
 +!text "hello there,                            "
 +!text "what you can see here is an upward      "
 +!text "scrolling message, which consists of 1x1"
 +!text "characters.                             "
 +!text "                                        "
 +!text "this message can either be long or short"
 +!text "but you must make sure that the number  "
 +!text "of characters = 40 per text row         "
 +!text "otherwise you will get strange results  "
 +!text "                                        "
 +!text "okay, message resets ...                "
 +!byte 0
base/1x1_upscroll.txt ยท Last modified: 2021-06-11 15:32 by richard