2000x would be better too ;-) The code ends with RTL, reset MX and emulation code too. Just wondering if (hope my S2 will support this... fu.. virtual kbd) Lda #0 Tax Pea bnkbnk Plb Plb Jsr checksum1.... Checksum call / keep clc where needed Here: Adc $0000,x Inx Inx Bne here: