D17B Computer Applications
C. H. Beck
Although the D17B does nor provide all the desirable features of large general-purpose machines, it does resemble them functionally and it possesses a number of similar features. It is a versitel multiplurpose computer capable of solving a wide range of problems;1,2 however, it has limited capability both in storage capacity and computation speed. Unlike the large general-purpose computer which is designed to efficiently process many different programs, the multipurpose D17B is better suited to dedicated or fixed tasks that can be served effectively by economical use of the available memory and speed of execution.3,4
Consequently, the D17B, like commercial minicomputers with small memories, is not well suited for general-purpose computing when compared to a large computer.5 General-purpose computation in minicomputer terminology refers to stand-alone operation. Some minicomputers are used as stand-alone computers for scientific and engineering use, but most are used in real-time applications such as control, data acquistion, communication concentrators and processors, peripherial controllers and preprocessors for alrge computer systems, display controllers, buffer memories, bio-medical monitoring, automated testing, automated instrumentation and telemetry.6-23
In a practical sense, the capability for general computing is determined by the ability to perform a large variety of calculations. This ability, in turn, is determined basically byt he instruction set. Available subroutines simplify the programming, and assemblers and compilers simplify the task further. The goal in providing general-purpose software for the D17B is to minimize the amount of time, effort, and knowledge required for a user to arrive at a point of useful return for his investment in the development of the D17B. But, generality always comes at a prive. The D17B is limited at present to a small number of real-time, special-purpose machine language programs.
The apparent lack of speed is not such an importnat factor when the D17B is used as a dedicated control computer since much computing speed available in a large general-purpose computer is commonly lost in system overhead and I/O.24,25 Furthermore, the 4-bot and 8-bit parallel output data channels available on the D17B should prove to be very advantageous in communications systems that operate on 8-bit ASCII characters, because the overhead operations of packing and unpacking are minimized. The 24-bit double precision data word used on the D17B appears to have considerable utility for computation associated with these 8-bit codes for character representation which are now becomming standard. Therefore, the 24-bit word of the D17B not only offers more precision than most minicomputers, but it provides for outputting 8-bit submultiples.
Computer control applications may include monitoring and data processing, start-up and shut-down procedures, and optimal control. The m,ain attributes of computer control are computational speed, storage capacity, and decision-making ability. If sufficient computational speed is availabel, optimal control can be accomplished. The storage capabhility provieds for economical and efficient data recording and processing. Decision-making ability provides the capability for direct digital control.
A direct digital control system muse provide a means for measuring the condition to be controlled, compare the measured value with a desired value, and automatically cause the two values to agree. Data logging can be perfromed as one phase of the control operation. Feed-forward control requires the solution of equations which represent a predictive mathematical model. A control computer can also be usedfor supervisory functions such as start-up or shut down operations. Direct digital control requiresx that each variable be compared in turn with the desired values.
Logical decisions and constraints can be employed in computer control, and the results of intermediate calculations and control actions can be recorded to produce a historical file. The general-purpose capabilities of the D17B permit the control program to be modified and expanded within the limits of memory capacity to fit system growth, new instruments, or changing control policy.; The versatility available with a computer control system involving a general-purpose computer is an important consideration.
If the D17B is to be used for control computing applications, it must be capable of not only performing control calcuations, but a number of other essential functions also. For example, raw input data are generally subjected to individual limit checks to detect instrument failures or out-of-normal conditions, averaged or smoothed to minimise the effects of random variations, and then recorded or used in calculations. As a typical example of a limit check in terms of D17B instructions, the following could be executed:
These four instructions would accomplish the limit check by performing a conditional branch. Similar operations could be equally useful for general of special-purpose computing.
It is appropriate that the D17B be considered for dedicated control applications involving control over a single unit or a limited portion of a process. Such an application may not only be appropriate considering the limited memory and execution speed of the D17B, but the system reliability consideration makes D17B's ideally suited to such tasks. Process-wide control may require several interconnected D17B's. The real-time aspects of control applications is compatible with the current requirement of machine language programming for the D17B.
Considerable benefit can be gained by using dedicated comptuers which decentralize system design and simplify software requirements. The major advantage of using several dedicated control computers are the complete independence of each unit from failures in other units and the reduced sophistication required to program the computations. Dedicated control computers make automated start-up a practical consideration.
Since A-D and D-A converters and multiplexers are required for each computer, the use of several dedicated D17B's could represent too large an expenditure in conversion equipment. But, because conversiona nd other subsystem costs may have been reduced considerably, the use of several dedicated computers appears toi be feasible. Delays caused by breakdown can be avoided by using a dedicated on-line machine, and there is no question abour program security.
As new instruments are added and as knowledge of a process increases, better control policies can be developed. Hence, control programs are constantly in need oc change. Also, the characteristics of the process will often change as its operation is improved through computer control. Because of these factors, the programmable feature of the D17B is extremely desirable as well as its flexible I/O capabilities, which can accomodate a variety of control devices. The D17B can provide digital, pulse-type, and analog output signals under program control for manipulating process variables. This flexible I/O capability provides for efficient interaction between the D17B and the devices being controlled.
In addition to capabilities required for general computing applications, control computing applications require a flexible I/O structure to accomodate a variety of devices. As described previously, the I/O capability of the D17B is extrememly versatile.
For real-time control applications, the D17B must be able to accept and process input data sufficiently fast that the results of this processing can be used to influence and control the appropriate variables. The D17B was designed to accomplish real-time computation as required for missile guidance; however, the bandwidthe of the particular application will dictate the speed requirement. The D17B performed real-time communication with external devices such as velocity meters, accelerometers, and D-A converters to obtain data and issuel commands necessary for navifation, guidance, telemetry, and control functions.
As indicated in the specifications, the D17B has a maximum I/O data rate of 25,600 words per second. Direct data entry is also provided. Hence, within the limits of its capabilites the D17B appears to be very appropriate for a variety of control and special-purpose applications.
Certain special-purpose applications such as on-line digital data processing, computer interfacing, peripheral buffering, and data monitoring require very little CPU sophistication, limited arithmetic capability, and perhaps low-speed performance compatible with the D17B specifications. THe dominant requirement of many special-purpose computer applications relates to the I/O architecture as is the case for control applications. The importance of I/O channels is particularly significant where data is being transmitted continuously between the computer and peripheral devices.
On-line digital data processing often requires that analog information be converted to digital form using an A-D converter. With the 24-bit double precision word of the D17B, the output from two 12-bit A-D converters can eb sinputted simultaneously under program control. The requirred speed of I/O transfers and arithmetic or special-purpose data acquisition can eb much slower than for control applications because real-time analysis and control response commands are not necessary. Hence, the D17B is flexible enough to be used int hese areas formerly requiring special-purpose computers. As requirements change, the D17B can easily be re-programmed. In such fields as medical research, biological studies, and experimental physicals, the D17B can be programmed to control the monitoring, measuring, and recording of a variety of quantities such as pressures, flow rates, EKG, and heart rate. Automation of chemical laboratory instruments such as chromatographs, spectrometers and AutoAnalyzers using the D17B also appears feasible. Calculation of desired parameters, recording of results, and graphic display are appropriate applications areas for this computer. Simultaneous measurements of several quantities are possible through the use of sample-and-hold devices, a multiplexer, and an A-D converter.
A flexible, reliable, mobile data monitoring system can be developed using the D17B computer with interface to any of the following: operational amplifiers, sample-and-hold devices, multiplexers, analog-to-digital converters, digital voltmeters, counters, CRT displays, polotters, programmable signal generators and power supplies, transducers, and sensors. This combination will provide for the automatic testing of electronics components, IC, logic cards, compelte logic assemblies, and other devices and circuits. Programmed transducer testing and high-quality data collection of signal characteristics such as amplitued, current, and phase which can be accomplished at high speeds have significant advantages over manual methods. These techniques are also applicable to non-destructive testing as employed in the inventory of aircraft parts based on the characteristics of the steel as represented by the electrical output of spectrometer-type instruments.
On-line communcation is also an important applications area to be considered for the D17B. A data-concentration buffer storage system for teletype and other low-speed I/O devices can be developed. Programmed multiplexing of parallel information for serial transmission over a narrow-band communication channel is possible since the D17B can provide for changing the scan rate. Preprocessing for analysis and computation by a large-scale computer will also be an appropriate consideration.
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