[1] : The Free On-line Dictionary of Computing (27 SEP 03)

zilog z8000
     
         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
     
     
see also:
microprocessor zilog intel 8086 segment registers mmu registers 
stack pointer operating system interrupt zilog z80 dram refresh 
bugs microcode pipelined zilog z80000 

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