cessed command chars
:
  ldx #$00    ; first char 

; --- A --- crsr up       
  cmp #$41    ; A?
  bne @not_A
  jsr get_number_from_esc_seq  ; get argument
  lda escape_parameter    ; escape_parameter = 0...
  bne :+
  inc escape_parameter    ; .. means 1
:
  lda $d6     ; get crsr row        
  sec
  sbc escape_parameter    ; row = row - up
  cmp scroll_region_start     ; stop at top of ..
  bpl :+    ; ..scroll region
  lda scroll_region_start    
:
  tax         ; x is row
  ldy $d3 