On 7 Oct 2012 at 18:34, mike delyea wrote: > Does the Q accumulator mean the 6309 can address 32 bit memory? No the Program counter is still 16 bits thus 64K of memory space. To access outside a 64K memory space you have to use a MMU (Memory Management Unit). The Q register is most useful in doing 16 by 16 bit multiply or in doing the 32 by 16 bit divide. james