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

zilog z80
     
         an 8-bit microprocessor.  it was released in
        july 1976 with a 2.5 mhz clock rate.  the z80 was a much
        improved intel 8080 as was the intel 8085.  it also used
        8-bit data and 16-bit addressing, and could execute all of the
        8080 op codes as well as 80 new ones, instructions that
        included 1, 4, 8 and 16-bit operations and even block move and
        block i/o instructions.  the register set was doubled, with
        two banks of registers including a and f that could be
        switched between.  this allowed fast operating system or
        interrupt context switches.  it features 3 types of
        interrupt mode.
     
        the z80 also added two index registers ix and iy and
        relocatable vectored interrupts via the 8-bit iv register.
        like many processors including the 8085, the z80 featured
        many undocumented op codes.  chip area near the edge was used
        for added instructions, but fabrication made the failure of
        these high.  instructions that often failed were just not
        documented, increasing chip yield.  later fabrication made
        these more reliable.
     
        the thing that really made the z80 popular was the memory
        interface - the cpu generated it's own ram refresh
        signals, which meant easier design and lower system cost.
        that and its 8080 compatibility and cp/m, the first
        standard microprocessor operating system, made it the
        first choice of many systems.
     
        in addition to the original z80 2.5 mhz there are the zilog
        z80a 4 mhz, zilog z80b 6mhz and zilog z80h 8 mhz
        versions.  the popular hitachi hd64180 processor family adds
        peripherals and an mmu to the z80.
     
        the zilog z280 was an enhanced version with an mmu and
        many new op codes.
     
        the z80 was used in the first nintendo game boy.  a
        sharp z80 work-alike was used in the gameboy color,
        running at 4 mhz for gameboy software or at 8 mhz for game boy
        color software.  the z80 was used in the sega master system
        and the game gear.
     
        gaby chaudry z80 site http://www.gaby.de/z80/.
     
        2003-07-11
     
     
see also:
microprocessor clock rate intel 8080 intel 8085 8080 op code 
register set operating system interrupt context switch index register 
vectored interrupt 8085 ram refresh cp/m 
zilog z80a zilog z80b zilog z80h hitachi hd64180 mmu 
zilog z280 nintendo game boy sharp gameboy color 
sega game gear lt;gaby chaudry z80 sitegt; 

Zilog >> Z Words
Zilog, definition of term: Zilog
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Z80 >> Z Words
Z80, definition of term: Z80
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