Yes, NOP is just an XCHG AX, AX. For instructions such as XCHG, the microcode doesn't know anything about the specific registers; hardcoded circuitry substitute

Yes, NOP is just an XCHG AX, AX. For instructions such as XCHG, the microcode doesn't know anything about the specific registers; hardcoded circuitry substitutes the registers from the instruction. This saves on microcode size. Microcode also doesn't know about 8-bit vs 16-bit instructions; that is also done in circuitry. As far as XLAT, I haven't seen anything yet to answer your question. I hope to figure out the microcode, which should provide more details.