Zilog Z8000
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The Z8000 was a 16-bit microprocessor introduced by ZiLOG in 1979. It was designed by Masatoshi Shima and was one of the last computer systems architected by a single person. It was not Z80 compatible, and although it saw steady use well into the 1990s, it was never very popular.
Although fundamentally a 16-bit architecture, some versions had 7-bit segment registers that extended the address space to 8 megabytes.
The register set consisted of 16 16-bit registers, and there were instructions that could use them as 8-bit, 16-bit, 32-bit, and 64-bit registers. The register set was completely orthogonal, with register 15 conventionally designated as stack pointer, and register 14 for stack segment.
There was both a user mode and a supervisor mode.
Like the Z80, the Z8000 included builtin DRAM refresh circuitry, but although an attractive feature for designers of the time, overall the Z8000 was not especially fast and had some bugs, and in the end it was overshadowed by the x86 family.
One notable use of the Z8000 series was by Namco in the design of its famous Pole Position series of racing videogames. Two Z8002's (small-memory versions of the Z8000) were incorporated into the design.
The reported inclusion of the device within military designs (source:TechWeb [1] (http://www.techweb.com/encyclopedia/defineterm.jhtml?term=Z8000&_requestid=203718)), perhaps provides an explanation for the continued survival of the Z8000 today, in the shape of the Z16C01/02 Serial Communication Controllers. Indeed, an active order code and datasheet may still be located upon the ZiLOG website.
The Zilog Z80000 was a 32-bit follow-on design.