Zilog Z8000

<processor> A microprocessor from Zilog introduced not long after the Intel 8086, but with superior features. It was basically a 16-bit processor, but could address up to 23 bits in some versions by using segment registers (to supply the upper 7 bits). There was also an unsegmented version, but both could be extended further with an additional MMU that used 64 segment registers. Internally, the Z8000 had sixteen 16-bit registers, but register size and use were exceedingly flexible. The Z-8000 registers could be used as sixteen 8-bit registers (only the first half were used like this), sixteen 16-bit registers, eight 32-bit registers, or four 64-bit registers, and included 32-bit multiply and divide. They were all general purpose registers - the stack pointer was typically register 15, with register 14 holding the stack segment (both accessed as one 32-bit register for painless address calculations). The Z8000 featured two modes, one for the operating system and one for user programs. The user mode prevented the user from messing about with interrupt handling and other potentially dangerous stuff. Finally, like the Zilog Z80, the Z8000 featured automatic DRAM refresh circuitry. Unfortunately it was somewhat slow, but the features generally made up for that. Initial bugs also hindered its acceptance (partly because it did not use microcode). There was a radiation resistant military version. There was a later 32-bit, pipelined version, the {Zilog Z80000}. (1997-12-16)

<company> The microprocessor manufacturer who produced the Zilog Z80 in July 1976 (as used by Sinclair in the ZX-80, ZX-81 and ZX Spectrum computers) and later the Zilog Z8000. Zilog was founded in 1974 and became a wholly owned subsidiary of Exxon Corp. by 1980. The company's management and employees purchased Zilog back from Exxon in 1989. Zilog became a publicly-held company in February, 1991. In March of 1998, Zilog was privatised, as a result of the merger and recapitalisation transaction by Texas Pacific Group (TPG). Zilog now produce a range of 8-bit microcontrollers, 8-, 16- and 32-bit microprocessors, and digital signal processors, covering the home entertainment, communications, and {embedded systems} markets. http://zilog.com/. Address: 910 East Hamilton Avenue, Suite 110, Campbell, CA 95008, USA. (1998-09-14)