wrap ---
  inx         ; increase line
  stx $d6
  ldy #$00    ; begin of line
  sty $d3
  jsr set_line_vectors
  ldx temp_ptr_x ; set screen line
  ldy temp_ptr_x+1
  stx $d1
  sty $d2
  ldx temp_ptr_y ; set colour line
  ldy temp_ptr_y+1
  stx $f3
  sty $f4        
  jmp end_plot_char
; --- scroll up ---        
@scroll_up:
  jsr scroll_up_scrollregion
  ldy #$00    ; begin of line
  sty $d3
  jmp end_plot_char
  


scroll_up_scrollregion:
  ldx scroll_region_start     ; get first