When an interupt occurs, the CPU jumps to the address stored in memory at I*256+databus. However, what happens to bit 0? If I=&FF and the data bus is &FF, is the vector fetched from &FFFE/&FFFF (ie, bit zero forced to 0) or from &FFFF/&0000 ? I have seen documentation, programs and (importantly!) emulators written declaring both to be true. Zaks says bit 0 is forced to zero (p504). Leventhal says bit 0 is forced to zero (p12-5). Penfold says "bit 0 is always 0" without saying if it is forced to zero (p34), or the hardware should always *supply* a zero. Zilog is silent (p145).