zilog z8000
zilog z80000
zilog z80a
Free On-line Dictionary of Computing:
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 switch
es. 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)
