Assembly question

[slenkar]

scrolling 8 lines:

Code:

function FASTCALL drawthis() as ubyte
asm


LD HL,2000
LD (delayiter),HL
LD HL,16384

drawvert:
LD A,31
LD L,A
LD (screenwidthiter),A

drawblokes:

LD A,(graphic)
DEC A
LD (graphic),A
LD (HL),A



LD BC,(delayiter)
wait1:
    dec BC
    ld a,B
    or C
    jr nz, wait1


LD A,(screenwidthiter)
LD L,A
DEC A
LD (screenwidthiter),A
LD B,A
INC B
INC B
INC B
djnz drawblokes

LD A,(screenheightiter)
LD L,A
INC H
DEC A
LD (screenheightiter),A
LD B,A

INC B
djnz drawvert



LD A,31
LD (screenwidthiter),A
LD A,7
LD (screenheightiter),A


LD HL,60000
LD (delayiter),HL

LD HL,16384
LD (screenaddress),HL



screenvert:


LD A,31
LD L,A
LD (screenwidthiter),A

screenhori:
;shift graphic
LD A,(HL)
RLA
LD (HL),A
LD A,(screenwidthiter)

LD L,A
DEC A
LD (screenwidthiter),A
LD B,A
INC B
INC B
INC B
djnz screenhori

LD A,(screenheightiter)
INC H
DEC A
LD (screenheightiter),A
LD B,A
INC B
INC B
djnz screenvert

DEC H
DEC H
DEC H
DEC H
DEC H
DEC H
DEC H
DEC H

LD A,7
LD (screenheightiter),A


jp screenvert

    end asm
end function

drawthis()

Print "done"

STOP

ASM
blockiter:
defw 8
delayiter:
defw 60000
screenwidthiter:
defb 31
screenheightiter:
defb 8
scrolliter:
defw 10000
graphic:
defb 255
screenaddress:
defw 0
end asm

why does it wrap around? thats like a bit shift affecting the byte next to it?!?!