When I learned Z80 assembly to program my TI-83, every byte of machine code counted, because the whole calculator only had 24k of storage. To initialize the mai

When I learned Z80 assembly to program my TI-83, every byte of machine code counted, because the whole calculator only had 24k of storage. To initialize the main accumulator register, `a`, to zero, you would do `XOR a` instead of `LD a, 0`. For the math instructions, `a` is an automatic operand, so `XOR a` XORs `a` with itself, and the entire instruction is only 1 byte. To explicitly load 0 into `a` requires the literal 0 to be represented in the opcode, so `LD a, 0` is a 2 byte instruction.