3 ms·

"The 68000 uses much wider microcode (85-bit microinstructions compared to 21 bits in the 8086)." is not what I remembered. Another source says "The actual int

• kens 4y ago
  My source is "The Architecture of Microprocessors", which has a very detailed chapter on the internals of the 68000. Each micro-instruction consists of a 17-bit sequencing field and a 68-bit action field (85 bits in total). These are stored in two separate sections of the microprogram ROM (what other sources call the "microcode" and the "nanocode"). The sequencing field specifies the next microcode address based on various branch conditions, while the action field controls the various parts of the CPU. I've seen descriptions like yours saying that the microcode dispatches to the nanocode, but I can't figure out how to make both descriptions consistent. "The Architecture of Microprocessors" is extremely detailed, describing the action of each field at the bit level, while other sources are more hand-waving, so I'm more inclined to believe it. But I haven't looked at the 68000 closely, so I could be wrong.