On Thu, Apr 26, 2018, 15:59 Bill Gunshannon via cctalk < cctalk@classiccmp.org> wrote:
> I believe the Z-80 was subordinate to the M68K. In high-level conceptual term, maybe, depending on the software. In term of the actual capabilities of the hardware, the Z80 was firmly in control of _everything_ in the machine, including control over the MC68000, while the MC68000 had no direct control over anything but its MMU (built from TTL) and memory. If code running on the MC68000 wants to talk to anything at all, disk, tape, console, printer, serial ports, etc., all it can do is politely request that of the Z80. In that sense it's like the CPU of a CDC 6600, which can't do anything without the PPUs The Model 16 was developed > independently of the Model II. The Model 16 was developed as an expansion of the already-existing Model II, with a few other changes like half-height floppy drives that were later implemented on the Model 12 also.