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zilog z80
(foldoc) | Zilog Z80
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. It was also used in the Sega Genesis
for hardware reverse compatibility with the Sega Master System
through a special cartridge.
Gaby Chaudry site (http://gaby.de/z80/).
(2004-06-10)
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zilog z8000
(foldoc) | Zilog Z8000
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)
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zilog z80000
(foldoc) | Zilog Z80000
A later version of the Zilog Z8000, expanded to
32 bits internally and with a 6-stage pipeline.
(1997-12-16)
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zilog z80a
(foldoc) | Zilog Z80A
A version of the Zilog Z80 microprocessor with
a 4 MHz clock rate.
(1995-04-24)
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