Zilog Z80
<processor> 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. It was also used in the Sega Genesis for hardware reverse compatibility
with the Sega Master System through a special cartridge.
Gaby Chaudry site.
(2004-06-10)
Nearby terms:
Zilog « Zilog Z280 « Zilog Z8 « Zilog Z80 »
Zilog Z8000 » Zilog Z80000 » Zilog Z80A
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