                          Life Beyond the Z80
                           by Howard Moftich

Since the Z80 was introduced in the 1970s, it has become the most widely
used 8-bit microprocessor in the world.  Of the millions used each year,
most are destined for CP/M machines.  (CP/M was originally developed for
the Intel 8080, but the Z80 is a significantly better processor and its
instruction repertoire is a superset of the 8080, so it will run the
same programs.)

In the past few years, the Z80 has lost its prominence to the Intel
8088/86 series of 16-bit processors, which form the heart of the MS/PC
DOS machines, and are not software compatible with Z80-based machines.
The 16-bit processors can address more memory than the Z80, which is
limited to 64K.  This larger addressable memory allows for faster
operation of application programs because more of the program resides in
memory rather than sitting on a disk which must be accessed (compare the
speed of operation of WordStar with memory resident editors like VDO).

Recently, Hitachi of Japan has introduced a new microprocessor called
the HD64180.  This processor is completely software compatible with the
Z80 (and therefore all CP/M) programs.  The new chip goes far beyond the
capabilities of the original Z80 by incorporating several peripheral
chips into its design.  The most significant of these additional
capabilities is the ability to address 512K bytes of memory.  This
additional space can be used for RAM disk or an application.  Other
goodies that are built into the chip are two Direct Memory Access (DMA)
controllers, two Serial Communication Interfaces (SCI's), a high speed
serial port and two programmable timers.  Previously, all of these
capabilities would have required five big chips to handle all the work
and lots of small chips to glue the system together.  The new chip
realizes very large savings in the space taken up on a printed circuit
board and the amount of power consumed.  The 64180, with all its
capabilities, uses about 10% of the power of a standard Z80 all by
itself.

The DMA controllers allow very high speed transfer of information from
the floppy disk, SCI's or memory without the processor's supervision.
This speeds the movement of data because the processor is quite slow
compared to the DMA.  The SCI's allow the ability to hook up a video
terminal and/or any other type of serial device such as a modem.  The
High Speed Serial Port is used to allow one 64180 to communicate rapidly
with another, or perhaps even with a slave processor that is controlling
another part of the system.  Lastly, the Programmable Timer permits real
time control of events or can be used as a real time clock.  Hitachi has
also designed the 64180 so that it requires less time to complete most
instructions than a standard Z80.  All these capabilities point to a
system that is faster and more compact than a Z80 system could ever hope
to be.

Several companies have already brought to market single board computers
based on the 64180.  The first is the SB180 from Micromint.  Although
most people believe that it originally appeared as a project in BYTE
magazine, the basic design came from Hitachi back in late 1984.  The
SB180 is a slightly upgraded version of the original design (remember,
you heard it here first!).  The board measures only 4 inches by 7 inches
and a complete 2-drive system (minus the video terminal) using 3.5"
drives can fit in a child's lunch box.   The second system is a drop-in
replacement for the Kaypro motherboard and supports color graphics and
almost everything else under the sun.  [Ed. note: For specs, price list,
and a discussion of the Z-system operating system, see SB180.TQT in area
B5 of the BOSKUG bulletin board.  Or write Micromint, 25 Terrace Dr.,
Vernon, CT 06066, (203) 871-6170.

Nor is this the end of the enhanced Z80 saga.  I hope soon to be
reporting about another Z80 compatible chip, the Zilog Z800.  If the
64180 is a "superchip," then the Z800 is an "ultrachip."  Originally
planned for 1981, we finally expect to see it early this year.  The
preliminary information indicates that this processor will use design
concepts normally found only in 16 and 32 bit processors, a clock speed
of up to 25 Mhz (the fast Kaypros run at 5 Mhz and the basic PC-AT runs
at 6 Mhz), and will come in a version that will address 512K of memory
and an enhanced version that will address 16 Megabytes of memory.

   Howard Moftich is an electrical engineer who designs radar signal
   processors and microcomputer hardware.
...from ONKUG, Newsdiskette to Kaypro Users Groups, Volume 2, Number 2.
