THE PET 2001 AND CAL: ITS USE IN THE PHYSIOLOGY LABORATORY

The microcomputer is probably talked about in education more than it is used-though this is certainly not for lack of available products. Indeed the flexibility of choice perhaps helps to generate the delay in use. A further factor may be the expertise required in both machine-code programming and in electronics. However these problems are essentially removed by the advent on ROM* of high-level languages, in particular good quality BASIC dialects, and of compiete packaged micro- systems. Thus CAL use of micros now seems ready for expansion. This paper first discusses what is perhaps the most eligible microsystem, Commodore’s PET 2001, and then describes some experiences of its use in tertiary-level ~b~s~olo~y teaching.

In 1977 MUSE ~n~i~~~~~~~~ter users in secondary ed~~~at~o~~ produced a series of guidelinesll] for m~~ro~omput~r systems in schools and colleges. Their tist (closed box, VDU i- 16 k store f cassette: expansion: safety: maii~tenan~: standardizations seems now to be almost a desolation of a PET. Qniy their cost estimate, expressed in terms of teachers’ salaries, is wrong: 1973 minimal system was 24 years salary; 1977. 5 months; PET, 6 weeks. The prime asset of the PET 2001 is in providing a complete microsystem, with ROM BASIC giving external file capacity, within a single portable box (Fig. 1). It can thus be readily moved between CAL, tutorial and laboratory use. The high quality BASIC language is used in its normal ‘monitor’ mode of operation, though of course jumps to machine code can be made as and if required.

362 I. C. H. SMITH

The built-in display unit with elements that are directly mapped to I k of store memory provides an amazingly flexible display system-which has often been recognized as a dominant requirement of successful CAL programs[2]. The PET screen has a grid of 40 characters by 25 lines compared with the usual VDU frame of 80 x 24 lines. In use this decreased resolution is adequately matched by the PET’s large set of graphics, upper and lower case characters (312 in all) and the speed and flexibility of a memory-mapped screen. In particular the graphics characters allow each cell to be divided into eighths (either by a single line or blocks and horizontally or vertically) thus allowing histogram-type displays with resolutions of up to 320 parts (40 x 8) by 25 lines. Division into quarter cells allows graphs of up to 50 x 80.

INTERFACING THE PET 2001

In the laboratory the PET offers four distinct types of interface with external data; (1) keyboard, (2) 8-bit bidirectional (‘user’) port with two flags, (3) main address and data bus and (4) IEEE-488 bus. Typical uses of these interfaces are; (1) data for statistical analysis, (2) simple S-bit D to A conversion with digital input, (3) memory-mapped multiple channel A to D and D to A converters and (4) high precision scientific apparatus.

The IEEE interface is a major innovation for microsystems as it allows the PET to be intercon- nected to a chain of passive and/or active devices, each device being treated as an external file to which one can INPUT or PRINT words. It is this facility which puts the PET high on the list of laboratory mjcrocomputer systems because there are many instruments, in particular the Hewlett- Packard range. which use the IEEE interface. Thus one can with relative ease connect an auto- spectrometer or high precision digital voltmeter to the PET and leave the pair to measure and calculate the results of an experiment. Note that the PET does not have a serial ASCII input/output (RS-232 interface) for ASCII communication with Teletypes or other computers: this sad lack can be overcome either by purchasing an IEEE to RS-232 adaptor or by microprogramming the pulse codes via a flag.

The crucial factors concerning on-line data machines are signal resolution (accuracy), the sampling rate (speed) and storage size (capacity). For the PET these may be considered crudely as & (l/256), 10 p’s and 8 k when working in machine code and IO- ‘%, 1Oms and I k when working in BASIC. Fortunately it is remarkably easy to jump to and fro between BASIC and machine code allowing optimisation of these resolutions. Much physiological data (e.g. heart activity, skin resistance, respi- ration, body temperatures) is within these limits and often an accuracy of greater than l-2% is of no relevance. Thus the laboratory systems can often make use of simple &bit interfaces. Physiolo~~l data also rarely has frequencies higher than 100 Hz: a major exception being nerve activity but here its digital nature reduces its speed-accuracy product to similar limits (500-1000 baud). The PET thus has data throughput characteristics similar to the chart recorders normally used in class experiments and a capacity, on the same analogy, of about 1 m of chart paper on RAM storage (4 k items) and about 20 times that on cassette tape.

Analog interfaces using the IEEE bus are available from 3D Digital Design (43 Grafton Way, London, WlP 5LA: 8 channel D to A, f300; 2 channel D to A for plotter, f260; 16 channel A to D, 6300; 12 bit A to D in development). Alternatively construction is relatively easy using memory- mapped systems such as the Burr-Brown MP21 (16 channel input) and MP 11 (2 channel output). The user port perhaps provides the simplest laboratory interface, the flags being used for event-type input (e.g. the QRS wave of the electrocardiogram) and the S-bit port for a D to A coonverter (Radiospares ZN425E). An internal edge-sensitive trigger can be used as an alternative to an external bistable. This trigger can also be used to internally generate tone bursts.

COSTS

Several reports, in particular that of the financial evaluation of the Nationaf Development Pro- gramme in Computer Assisted Learning[3] have made it clear that CAL should be treated as an additional form of teaching with an add-on cost: it cannot be considered as saving staff time, but has the dual role of effective teaching and developing student appreciation of computer applications. The financial essence of CAL is thus to provide the facilities at minimum cost.

It is undoubtedly the low initial cost of the PET (reduced recently to about f.500) that provides the first attraction. However further analysis continues to show its financial advantage. Economic con- siderations in choosing different computer systems have always been complex. In terms of capital costs the larger the system, the larger the cost per terminal (say EIOOO, f15OO,f2000, 1 k, 1.5 k, 2 k for micro, mini, mainframe respectively) but the facilities also increase (larger files, faster printers, etc.). The establishment costs also increase with computer size; a set of micros can be moved around from

The PET 2001 and CAL: Its use in the physiology laboratory 363

laboratory to tutorial room as required, a mini will usually need a specific teaching room for it and the terminals whereas a mainframe needs that and specific staff to run it. The annual operating costs (mail~tenance, operators, insurance), which NDPCAL found to be more than double the capital depreciation cost, all increase in proportion to capital and establishment costs. So one is left with the question, is the increased cost of larger systems merited by (a) increased reliability of operation, (b) increased facilities or (c) increased long-term stability of equipment? I believe it is only the last factor that is a significant argument against the introduction of microsystems as the main CAL technology. In terms of reliability a set of micros provides only distributed failures rather than the -occasionally frequent-catastrophic failure of larger systems. A microsystem such as the PET can usually match the computing power needed for CAL with two main exceptions-high resolution graphics (e.g. 256 x 256) and faster cycle times, especially within BASIC. Since it seems probable that 16-bit IO mHz microsystems will soon reach the market (ideally with a subprocessor for graphics) it is difficult at this time to predict that the PET will be adopted as a major CAL standard. Nevertheless it should be remembered that (a) Commodore will be interested in such enhancements of PET, and (b) there already exists a rapidly growing number of PET educational programs. The PET is an

extremely economic proposition and should be considered for many CAL tasks.

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Fig. 2. AXON. based on CUSC program by A. Wood, showing ionic currents in voltage-clamped squid axon as predicted by the Hodgkin-Huxley equations.

364 1. C. H. SMITH

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Fig. 3. HEART. Histogram of time interval between heart beats and statistics over a chosen time period. Button 3 refers to external interface.

APPLTCATfONS IN THE PHYSIOLOGY LABORATORY

Physiology can perhaps best be described as the physics of the biological sciences-how hving things work. As a direct consequence its students need simuItaneously to be able to handle the wealth of ideas and mechanisms in biology with the rigor of a quantitative model. In the undergraduate class, computers have been used as computational aids (e.g. best estimates of parameters of biological transport) or as an alternative to unethical or difficult experiments (MACMAN series and clinical decision making, voltage clamp of a nerve axon)r4J Microprocessors have been used at University College, London, for the class analysis of the electrical activity of buman muscle and for reaction timing. However the effort required to initiate the microprogram for such a system is rarely worth- while if the system is to be used purely for education.

The use of the PET as a CAL instrument has been demonstrated by the adaptations of many of the CUSC (Computers in ~I~dergrad~Iate Science ~urrjculurn)r~~ biological programs. Adaptations are necessary mainty to fit the reduced PET screen size-but also to make better use of the memory- mapped screen. One such program, AXON, displays the ionic current flowing through nerve mem- branes under voltage ctamp conditions (Fig. 2). Its PET version retains its full teletype accuracy but has been rearranged so that the program can run more easily as a complete third year practical class.

Alternatively the machine may be used as an analytical adjunct to a real experiment. HEART (Fig. 3) is an on-line program which measures the interval between each heart beat of an experimental animal and progressively displays a histogram of these intervals, After a chosen length of time statistics about the mean heart rate are generated so that the student has immediate quantitative

Fig. 4. PI;LSE. (Al Beat-by-beat red-time pfot of ~e~~~j~n~~j~ between heart rate and lung volume. (13) Dialogue using the digitai trigger circuit.

The PET 2001 and CAL: Its use in the physiology laboratory 365

information for determining if different drug treatments or doses have significantly different effects. A rather more ambitious program of this type, PULSE, demonstrates directly the relationship between variation in heart rate and lung ventilation (the latter being measured as the pressure from a closed tube strapped round the chest). The cardiac acceleration seen during the early phase of inspiration (‘sinus arrythma’) develops as hysterisis loops during progressive breathing cycles (Fig. 4A). The graphical resolution here is only 40 x 20 points but this proved entirely acceptable in use. A useful byproduct of the program was the development of a digital trigger circuit for the ECG signal (Fig. 4B).

A third type of use is simply as an intelligent calculating machine. BEST LINE, for instance, not only calculates the best straight line fit to 2 sets of data but also displays in rough graph form all the data points and the best line (after each paired data entry), allows full editing or removal of any mistaken entries and allows complete transforms of either X or Y data set-such as log, square or swap X/Y. Thus it becomes very much easier to show to the student the relevance of the statistical tests he makes.

The overall experience gained is of a machine with as much capability as normally wanted and which leads you further. Its prime drawbacks are the lack of a cheap printer and of high resolution graphics. The speed of the machine in BASIC (although faster than most other &bit machines) can also be limiting for programs using multiple loop calculations. These have proved to be of small cost to the benefit obtained.

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REFERENCES

Atherton R., Comput. Educ. 28, 10 (1978). McKenzie J., Elton L. and Lewis R., f~lteractioe Computer Graphics iu Scirnce Teachirtg. Ellis Horwood, Chichester (I 978). Foelden J. and Pearson P. K., The Cost of Lrarrting with Compufers. Council for Educational Technology, London (1978). Wood A. W., Computers in Undergraduate Physiology Teaching. University of London, Board of Studies in Physiology (1978). Lewis R., Computing in the Life Sciellces-Applicatiorls in Rrsrurch and Education. Croom Helm, London (1978).