fsphil

<?xml version='1.0' encoding='utf-8'?>
<?grc format='1' created='3.7.10'?>
<flow_graph>
  <timestamp>Sat May  6 22:17:54 2017</timestamp>
  <block>
    <key>options</key>
    <param>
      <key>author</key>
      <value></value>
    </param>

fsphil

<?xml version='1.0' encoding='utf-8'?>
<?grc format='1' created='3.7.10'?>
<flow_graph>
  <timestamp>Sun May 28 10:56:33 2017</timestamp>
  <block>
    <key>options</key>
    <param>
      <key>author</key>
      <value></value>
    </param>

fsphil

ov = $90 ; == $40, initial value for the overflow counter
ct = $D5 ; == $27 / 39, number of passes. Decrementing, finished at -1
sp = $D1 ; == $07C0, pointer to the bottom line (only set after scolling)

* = $02E5

scroll: jsr $E8EA
loop:   ldy ct
        lda #$A0
        sta $D020, y

fsphil

ov = $90 ; == $40, initial value for the overflow counter
ct = $D5 ; == $4F / 79, number of passes. Decrementing, finished at -1
sp = $D1 ; == $07C0, pointer to the bottom line (only set after scolling)

* = $0304 - (end - scroll)

scroll: jsr $E8EA
loop:   ldy ct
        lda #$A0
        sta $D020, y

fsphil

ov = $0D ; == $FF, initial value for the overflow counter

* = $0304 - (end - scroll)

scroll: jsr $AAD7 
loop:   lda #$A0
        sta $D3E0 - $80, x
        sta $0400+40*24+39-$80+1, y     ; incrementing rower, y finishes with value $80
        sta $0400+40*24-$7B-1, x        ; decrementing rower, x finishes with value $7b