Does anyone know of any side effects to ldir? I replaced this code: Label1: ld hl,SomeAddress ld de,_OP1 ld b,12 Label2: ld a,(hl) ld (de),a inc hl inc de djnz Label2 ret With this: Label1: ld hl,SomeAddress ld de,_OP1 ld b,12 ldir ret When i change it, the new program crashes my calc, but the old one didnt. Why is this? They are virtualy the same thing right? Thx to anyone who can help.