ZiLOG Z80 Handbook page 251

de facto standard bus since MITS, Inc. produced the first hobbyist
microcomputer, the MITS 8800, using the 8080A as a base. The sig-
nals defined for their system bus, many of which are identical or
very much related to the 8080A pin signals, have become the MITS
bus. As 100 pins are involved (and because other manufacturers are
reluctant to promote competitors), the bus also has become known
as the S-100 bus. Cromemco and Technical Design Labs products
will, therefore, operate compatibly with other products that have
been designed for the S-100 bus, and there are a great many such
products.
The Digital Group, however, has established their own bus which
is not S-100 bus compatible. There are both advantages and disad-
vantages to this. If a microprocessor is widely different from the
8080A-related bus, then much logic has to be devoted for conversion
from the microprocessor logic signals to S-100 bus signals. Subse-
quent timing problems and bus status problems also have to be dealt
with. On the other hand, if a module is S-100 bus compatible, then
a system user may utilize all of the diverse products available for the
S-100 bus in his system, ranging from speech synthesizers to special-
purpose I/O interfaces. Fortunately, the Digital Group offers a wide
variety of modules for their bus and this disadvantage is somewhat
alleviated.
The fourth manufacturer, Radio Shack, offers a turnkey micro-
computer system available to the computer hobbyist or small busi-
ness user only in assembled form. The bus, of course, is not an S-100
bus, although an interface between the Radio Shack system and 5-
100 bus may be made available.
The following discussion is not meant to compare the four manu-
facturers point by point, but rather to provide a factual description
of what is currently being offered by each. Since the microcomputer
market is so dynamic, these descriptions will suffer with time, but
should provide some guidelines to the reader in making an evalua-
tion of Z-80 microcomputer equipment.
TECHNICAL DESIGN LABS, INC.
Technical Design Labs' basic Z-80 module is the TDL ZPUTM card
which is an S-100 bus-compatible CPU board. In addition to the
ZPU, TDL offers an S-100 16K byte memory card, and a System
Monitor Board, which contains a monitor, RAM, and I/O porting.
In addition to the Z-80 modules, TDL has a mainframe microcom-
puter, the TDL XITAN Microcomputer, which provides a system
package based on the Z-80 modules. While not offering a great deal
of I/O hardware at this time of writing. TDL software appears to
be very impressive. TDL offers a monitor, a line and character-
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