Scroll for SCR1  or  SCR2 with character set repeated
======================================================

buf [768] = buffer in RAM of 768 bytes
aux [ 32] = buffer with new 32(vert) or 24(hor) chars

; ***     FIRST PART (MOVING)   ***
UP: hl = buf[ 32]   de = buf[  0]   bc = 736  ldir
DN: hl = buf[735]   de = buf[767]   bc = 736  lddr
LT: hl = buf[  1]   de = buf[  0]   bc = 767  ldir
RT: hl = buf[766]   de = buf[767]   bc = 767  lddr

; ***   SECOND PART (FILLING)   ***
UP: hl = aux        de = buf[736]   bc = 32   ldir
DN: hl = aux        de = buf[  0]   bc = 32   ldir
LT: hl = aux        de = buf[ 31]   bc = 24   loop: ldi
RT: hl = aux        de = buf[  0]   bc = 24   loop: ldi
LT/RT:     ; Extra code por LT or RT
loop: ldi
    ld    a,e
    add   a,31
    ld    e,a
    jp    nc,de_ok
    inc   d
de_ok:
    ld    a,c
    or    a
    jp    nz,loop

; ***   THIRD PART (SHOWING)  ***
    in    a,(99h) ; clear F flag
waitf:
    in    a,(99h)
    and   080h
    jr    z,waitf ; wait scan end
    xor   a
    out   (99h),a
    ld    a,18h + 40h
    out   (99h),a
    hl  = buf                     bc = 098h   3*otir

; ***   FOR DIAGONAL SCROLL   ***
Execute 1st/2nd parts for first  direction
Execute 1st/2nd parts for second direction
Execute 3rd part