* Conditional jumps are only 8-bit relative. And unconditional jumps are only 16-bit absolute.
* LDX abs,Y and LDY abs,X instructions exist but not the corresponding instructions STX abs,Y and STY abs,X. As we have seen in the opcode table, it's most probably because they are broken.
* The CLV (Clear Overflow Flag) instruction exist but not the SEV (Set Overflow Flag) instruction.
