Design of the Bx-272 Integrated-Circuit
Control Computer
V. C. KAMM Demanding requirements are imposed on the computer used in automatic photo-
A. J. FOLAND grammetric plotting. This paper discusses these requirements and the new Bendix
J. R. VAN ANDEL Bx-272 real-time control computer designed to meet these and other demanding
L. W. BEHR control requirements. Input-output capabilities, logic organization for fast real-time
BR. E. CHILDS performance, and special instructions to enhance these features have received particu-
lar attention. The basic computer includes a real-time clock, multilevel interrupt
sensing, direct memory access at rates up to 1.6 million words per second, and
power-failure protection. This paper discusses performance characteristics, expansi-
bility, and compatibility with various peripheral equipment, including data links with
large-scale data processing systems and data banks, as well as some potential uses of
the Bx-272 computer.
INTRODUCTION
Bendix Research Laboratories has recently com-
pleted the development of the Bx-272 integrated-
circuit control computer. The Bx-272 is basically a
high-speed, general-purpose computer which is in-
tended primarily for real-time control applications.
However, it is extremely capable as a general-purpose
computer for scientific calculations. A variety of
peripheral input-output equipment and supporting
software has been developed to enhance its usefulness
in these areas.
For more than a decade, Bendix has been engaged
in the development of digital control techniques for
real-time applications. Some of the earliest develop-
ments were the design of special-purpose, digital
data-handling systems for the numerical control of
machine tools. Later on, special-purpose digital com-
puters were developed and produced for use in con-
trolling photogrammetric instruments, particularly
analytical stereoplotters. Today, with the advent of
fast, low-cost core memories and integrated digital
circuitry, it has become economically feasible to
design a general-purpose control computer with suf-
ficient capability to handle any of the former control
problems as well as many others.
The Bx-272 computer is capable of controlling
automated or manually operated stereoplotters. In
fact, it could control several manually operated
stereoplotters simultaneously. At the same time, it
could control an on-line data link between these
stereoplotters and a central data-bank. These are just
a few examples of the flexibility and growth potential
now available for photogrammetric applications.
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Other possible data-handling and control tasks which
could be readily accommodated include process con-
trol systems, simultaneous control of multiple ma-
chine tools, control of automated production lines,
automatic drafting, graphic display systems, and
various approaches to computer-aided design which
require an effective man-machine interface.
The next section of this paper summarizes the
general requirements and objectives that a computer
must meet for real-time control purposes. Succeeding
sections then describe the overall design of the
Bx-272 in the light of these factors.
DESIGN REQUIREMENTS AND OBJECTIVES
In designing the Bx-272 computer, the overriding
criteria were adequate performance and reliability to
accommodate a wide range of real-time control appli-
cations. Other requirements included an internal
organization to permit easy programming and ade-
quate arithmetic precision to be generally useful in
scientific calculations of an off-line nature. A parallel
goal was that the design should utilize widely avail-
able components and economical assembly tech-
niques.
In the most demanding real-time control applica-
tions, the control computer is placed within the
closed loop of a servo-like system. Therefore, the
speed and precision with which the computer can
solve the control equations and communicate with
the other portions of the system are critical to the
BENDIX TECHNICAL JOURNAL SUMMER 1968
