The synergistic combination of an oscilloscope and a microprocessor

The synergistic combination of an oscilloscope and a microprocessor by WALTER A. FISCHER Hel'}lett-Packard Company Colorado Springs, Colorado INTRODUCTION Osciiloscopes-What they are and what they do An oscilloscope presents a graphical display of amplitude vs. time. The amplitude is usually voltage. It allows the electrical designer to see what is occurring in a circuit. The CRT display was originally a qualitative one and provided the designer with an idea of what was occurring. Through improvements in vertical amplifier design, sweep linearity, and CRT performance, a calibrated graticule was added to the CRT face and quantitative measurements could be made. These improvements continued and resulted in measurement accuracies in the 2 percent to 3 percent category, with some timing measurements reaching the 1 percent area. These accuracies represent the state-of-the-art performance with traditional techniques. A new set of techniques was, becoming an obvious need in order to make major improvements in the measurement capabilities of oscilloscopes. Where major improvements in measurements are needed The two main categories where improvements are needed are measurement accuracy and ease of use. Measurement accuracy Oscilloscopes measure voltage and time related functions; such as, peak-to-peak voltage, percent overshoot, periods, propagation delay, etc. Timing measurement accuracy is the area where most customers have requested improvements. Specifically, the area of propagation delay. The reason is that a major part of electrical design tasks today are oriented to digital designs. One of the most important requirements for proper digital circuit performance is that information arrive at the various nodes in the system at a precise time. Even if the amplitude is in error, or contains overshoot, as long as the signal is timed properly at the logic threshold level, a good signal will be recorded. If, the threshold level arrives at the wrong time, this can cause major failures in system performance. It is necessary to measure precisely, the relative time delays of signals arriving at a point through different paths. Pulse 23 width, period, transition times, and clock rate must also be measured. The oscilloscope is still the best form of instrumentation to measure instantaneous voltages. It is also used to measure dc voltages as well as percent overshoots, and logic threshold levels. These measurements can now be made with oscilloscopes but not with any amount of ease and are subject to considerable human error. Such things as counting graticule lines and multiplying by the sensitivity of the CRT take time and are subject to human error. Ease of use One of the features of an oscilloscope is its versatility in making a large variety of measurements. This versatility has always required a large number of front-panel ~ontrois. This is its biggest problem. Most of these controls are manual, not only in function but also in their ability to allow the operator to make measurements, therefore it requires a great deal of thought on the part of the operator just to use the scope. It is possible on most oscilloscopes through a combination of controls to achieve completely useless modes. Even more of a problem is the fact that gross measurement errors can occur when the oscilloscope is in any of the "uncal" modes. These are just a few areas where major improvements in ease of use can be made. A SOLUTION TO THE MEASUREMENT ACCURACY AND EASE-OF-USE PROBLEM The newly introduced HP Model 1722A is a synergistic combination of an oscilloscope and a microprocessor and makes major contributions in measurement accuracy and ease of use. It is basically a 275 MHz high-performance oscilloscope with up to 1 nanosecond per cm resolution in the time base. The major contribution is timing measurement accuracy. Two things contribute to this, they are dual-delay sweep* and microprocessor control. Dual-delay sweep is a technique that allows the operator * Patent applied for.

::':. 24 National Computer Conference, 1975 o.. w :r':.. '.. ::... sweep markers. In the vertical section, when the vernier is placed in the "uncal" mode, the instrument automatically goes into the percentage measuring mode. These are just a few of the advantages of using a microprocessor in instrumentation. WHY A MICROPROCESSOR INSTEAD OF COMBINATIONAL LOGIC? a :1\.:: :::[1::<]\':1"> ': 1 3.0 \. '..... 1. ~:.~-l:..; -:.I-::H-++ _:-+--+-++++-+-hor-4"'i...~:j\i....:..,' ~ 2.0 '\.....,. :::::::\: W ""':':".::::~'I;, '.:.. 1::: ::--'.:,.... ;:.:.::::~~:..:,.2.. ~.. 1.0... ~. ~;: :.....~... :.:.. r::.;o;;~ ;;;;';';~ T1?"~ ::;:::~;;;;,:: : b o. 'I:' ''!'Io :: :::!:::~::::: N".. ~.. :::::. ii ::"~:i;;:.:::~.:::j;::::~~~~::jf~ ::;; :":';;:: ':<: Wi 0.1 1 10 Time Interval in Div Figure I-A comparison of the accuracy of time interval measurements of the HP Model 1722A and a conventional oscilloscope (a) Error curves for time intervals from 1 ns to 500 ns for (1) Conventional scope using differential delay techniques; (2) 1722A specification. Curves derived from optimum main time base settings for this measurement range. (b) Error curves for time intervals in terms of main time base divisions (100 nsf div to 20 ms/ div) to see, simultaneously, both the start and stop points of the time interval being measured whether it be period, pulse width, propagation delay, etc. This automatically eliminates the CRT as well as vertical or horizontal amplifier drift (or both) as sources of error. The microprocessor adds an order of magnitude (more accuracy) to the standard oscilloscope by providing greater resolution and readability than had previously been possible. Specifically, better than 1 percent measurements can be made on time intervals as small as 30 nanoseconds or 4 percent of full scale. Figure 1 shows a comparison of accuracy in graphical form of the Model 1722A and a high-quality standard oscilloscope of equivalent bandwidth. The microprocessor also presents direct digital readout of all measurements. Table I lists the measurement set of the Model 1722A. The gross measurement errors and useless modes previously referred to are remedied by the microprocessor. The Model 1722A monitors various front-panel controls and, when necessary, prevents incorrect measurements from being made. For example, when making a timing measurement, if the sweep is set to the "uncal" mode, the microprocessor senses this and sets the LED readout to (.0) and eliminates the stop marker of the dual-delayed There is no clear-cut choice. There are some advantages and disadvantages to each of these approaches. Combinational logic, because it is traditional, is often chosen when another approach should be considered. When many functions are required a large number of companents are TABLE I-HP Model 1722A Measurement Set I. Time Interval II. III. IV. A. Period B. Transition times C. Propagation delay 1/Time A. Clock rate B. Data rate DC volts A. Average voltage B. Direct difference voltage Instantaneous volts A. Peak-to-peak B. Threshold voltage V. Percent readout A. Percent overshoot B. Percent transition times C. Identifying 50 0 /0 points on pulses

The Synergistic Combination of an Oscilloscope and a Microprocessor 25 necessary. This can lead to power and heat problems. The major advantages of corn binational logic for small systems are knowledge and availability of components. Most electrical designers feel comfortable with this approach because they have used it traditionally. If only a few functions are required, combinational logic can be the best choice. The microprocessor approach, however, can make many functions available using fewer components. This usually results in higher reliability and lower power consumption. The major advantage of the microprocessor approach is its ability to perform mathematical operations. Many of the algorithms used by the Model 1722A require the use of mathematics (refer to the section on algorithms). Its major drawback is non-familiarity. The average electrical designer has little or no experience in programming at the assembly level and therefore tends to avoid it. In the past, it has been difficult to justify the training costs in light of the profit motivation of industry. This situation seems to be improving, however, as it becomes obvious that microprocessor based control systems can be inexpensive, reliable, and add measurement capability never before available. At this point, a case history might prove interesting. The curve in Figure 2 gives an indication of the decision to be made. With combinational logic, the cost increases in a somewhat linear fashion, depending on the number and complexity of the functions desired. With the microprocessor, there is a minimum amount of hardware necessary even if only one function is performed. As the number of functions increase, the cost increases at a rate far less than that of combinational logic. The steps indicate when a new block of memory needs to be added. This is because memory cannot be bought one word at a time but must be bought in blocks; e.g., 256 X 8 bits. An interesting area on these curves is the intersection. It is here that the microprocessor approach becomes obviously less costly than the combinational logic approach. In the case of the HP Model 1722A, this occurred in the display function. One of the requirements for this instru- Cost $ :::I '" ID :::I til ID!P $- Figure 3-Block diagram of the HP Model 1722A IL processor based control system ment was that the LED display present answers in a very special form of scientific notation; namely that the exponent could take on only values which were multiples of the number three. The time interval always can be read directly in s (0), ms (-3), JLs( - 6) or; ns (-9). This is shown in Figure 4 and Table II. The cost of doing this with combinational logic was high-therefore, the microprocessor approach was considered and found to reduce cost and package count, with far less power required. The choice of which approach to use must be made carefully. You may be surprised at the small number of functions it takes to justify a microprocessor-based system. BLOCK DIAGRAM OF THE MICROPROCESSOR BASED SYSTEM USED IN THE HP MODEL 1722A Number of Functions Figure 2-A comparison of the costs involved between combinational logic and IL processor based systems The technique employed in the Model 1722A was to use the microprocessor LSI circuits from the HP-35 calculator with a unique set of ROM's programmed to perform the

26 National Computer Conference, 1975 TABLE II -Time Base Encoder Program Listing ROM ROM ROM Subroutine Address Code Address Labels Program Statement L1006: 1 1 1 LSCA4 LOAD CONSTANT 1 L1007: 1 1 1 1 ->L1042 GOTOLS03 L 1010: 1 1 1 LSCA5 LOAD CONSTANT 2 L 1011: 1 1 1 1 ->L 1042 GOTOLS03 L1012: 1 1 1 1 ->L1041 LSCA6 GOTOLS02 L1013: 1 1 1 LSCA7 LOAD CONSTANT 1 L1014: 1 1 1 LSCA8 LOAD CONSTANT 2 L1015: 1 1 1 1 ->L1050 GOTOLS05 L 1016: 1 1 1 1 LSCA9 LOAD CONSTANT 5 L 1017: 1 1 1 1 ->L1050 GOTOLS05 L1020: 1 1 1 LSCBO LOAD CONSTANT 1 L 1021: 1 1 1 1 1 ->L1046 GOTOLS08 L1022: 1 1 1 1 ->L1044 LSCB1 GOTOLS06 L1023: 1 1 1 1 1 ->L 1045 LSCB2 GOTOLS07 L1024: 1 1 1 1 LRNG1 LOAD CONSTANT 9 L1025: 1 1 ->L1000 GOTOLRTNO L 1026: 1 1 1 1 LRNG2 LOAD CONSTANT 6 L1027: 1 1 ->L 1000 GOTOLRTNO L1030: 1 1 1 1 LRNG3 LOAD CONSTANT 3 L1031: 1 1 ->L 1000 GOTOLRTNO L1032: 1 1 ->L1000 LRNG4 GOTOLRTNO L1033: 1 1 1 LKBD1 8->P L1034: NO OPERATION L1035: 1 1 1 KEYS -> ROM ADDRESS L 1041: 1 1 1 1 LS02 LOAD CONSTANT 5 L1042: 1 1 1 1 ->L1062 LS03 JSBLDP4 L1043:. 1 1 1 1 1 ->L1051 LS04 GOTOLKBD2 L1044: 1 1 1 LS06 LOAD CONSTANT 2 L1045: 1 1 1 1 LS07 LOAD CONSTANT 5 L1046: 1 1 1 1 1 ->L1056 LS08 JSBLDP2 L1047: 1 1 1 1 1 ->L1051 GOTOLKBD2 L1050: 1 1 1 ->L 1060 LS05 JSBLDP3 L 1051: 1 1 1 LKBD2 1->P L1052: 1 ROM ADDRESS -> BUFFER L1053: 1 1 1 KEYS -> ROM ADDRESS L1056: 1 1 1 1 LDP2 10->P L1057: 1 1 1 1 1 1 ->L1063 GOTOLDPO L1060: 1 1 1 1 1 LDP3 11->P L 1061: 1 1 1 1 1 1 ->L1063 GOTOLDPO L1062: 1 1 1 1 LDP4 12->P L1063: 1 1 1 LDPO LOAD CONSTANT 2 L1064: 1 1 RETURN functions needed to accomplish the measurements listed in Table I. With this in mind let us discuss the block diagram of Figure 3. The primary function of the processor (Arithmetic & Register and Control & Timing) is to continuously scan the appropriate front-panel controls and output the proper signals to both the LED display and to the oscilloscope cir- cuits. The front-panel controls, therefore, are essentially a keyboard similar to the keyboard of the HP-35 and as such their outputs are encoded by the input interface to present particular memory addresses to C & T. Programs are stored at these addresses and perform the appropriate functions, such as, increment, decrement, output to the display, compute a time, etc.

The Synergistic Combination of an Oscilloscope and a Microprocessor 27 The BCD output of A & R is directed to the I/O control where two things occur. First, if data are being output, it converts the data from serial to parallel data and transfers them to buffer storage. Second, if the front panel controls are to be scanned, it decodes the outputs from the Processor and enables the appropriate sections of the front panel; such as, vertical range, timebase range, etc. The Buffer Storage and DAC receive data from the I/O control and provide temporary data storage and conversion to analog levels for the Analog Amplifier assembly. The Analog Amplifier performs two functions. First, it supplies the dual-delayed sweep comparators with the proper dc levels. Second, it accepts the dc level from the vertical channel, processes this level and provides two pieces of information for the processor through the Input Interface. The two pieces are the polarity of the dc level and whether the level is greater or less than some reference. If it is greater, the processor increases the reference until it is within llsb of the unknown. Conversely, if it is less, the processor decreases the reference until it is within llsb of the unknown. In both cases, it displays the reference level that is now equal to the unknown. SERIAL MICROPROCESSOR FOR OSCILLOSCOPE USE There are many microprocessors available on the market; why then, choose the serial microprocessor? One Figure 5-Data output algorithm for L\ T mode of 1722A reason was the fact that the HP-35 microprocessor was available as a high volume, fully documented microprocessor. Below are additional reasons for this choice. Display functions This was one of the major cost justifications for using a microprocessor. In the HP-35 serial microprocessor the complete decoder system, compatible with the basic instruction set, is resident in the LSI arithmetic and register circuit. A set of bi-polar cathode/ anode drivers are available, and sign and decimal location are also part of this chip set. Keyboard scanning Figure 4-Time base encoder flow diagram The keyboard scanning circuits are resident in the LSI and with one keyboard enable, 40 keycode inputs are possible. Since some of the internal status bits are available to the software programs, several keyboards can be overlayed with this approach. In the HP Mode11722A, for example, there are a total of six keyboards. The conversion of keycodes to ROM address is done within the control and timing circuit. Figures 4 and 5 and Tables II and III show that the program branches on an externally generated address; e.g., in Figure 4 at LI035.

28 National Computer Conference, 1975 TABLE III-Program Listing of Data Output Algorithm for 1722A ROM ROM ROM Subroutine Address Code Address Labels Program Statement LOO02: ->L0176 LFST1 GO TO LFSTM LOO03: -> L0201 LMED1 GO TO LMEDM LOO04: LZR01 1 -> S9 LOO05: -> L0211 GO TO LMODZ LOO06: LSL01 4 -> P LOO07: -> L0204 GO TO LSL02 L0010: LlNCP 1 -> S3 L0011: -> L130 GO TO LlNC1 lo013: 1 1 1 1 -> L0132 LDECP GO TO LlNC3 L0024: _> L0125 LOK JSB LKBD4 L0025: _> L0174 GO TO LKBD6 L0125: 1 1 LKBD4 ENCODE INCR/DECR CONTR. L0126: IA KEYCODE L0130: LlNC1 0-> S4 L0131: RETURN L0132: LlNC3 1 -> S3 L0133: LlNC4 1 -> S4 L0134: RETURN L0160: LAEC 0-> C[X] L0161: A + C -> C[X] L0162: A EXCHANGE C[WP] L0163: RETURN L0174: LKBD6 ENCODE MARKER RATE L0175: IA KEYCODE L0176: LFSTM 1 -> S9 L0177: LFSTN 6 -> P L0200: -> L0210 GO TO LSL03 L0201: LMEDM 1 -> S9 L0202: LMED2 5 ->P L0232: 1 -> L0210 GO TO LSL03 L0204: 1 LSL02 IF S9 # 1 L0205: 1 -> L0210 THEN GO TO LSL03 L0206: 1 1 -> S10 L0207: 1 1 0-> S9 L0210: 1 1 1 LSL03: LOAD CONSTANT 1 L0211: 1 1 1 LMODZ 7 -> P L0212: 1 IF S1 # 1 L0213: 1 -> L0263 THEN GO TO LMODO L0263: 1 1 -> L0160 LMODO JSB LAEC L0264: 1 1 DOWN ROTATE L0265: 1 1 1 -> L0160 JSB LAEC L0266: 1 1 1 1 1 1 -> L0372 GO TO LMODA L0372: -> L1373 LMODA SELECT ROM 1 L1303: LMOD1 0->8 C[X] L1304: IF S4 # 1 L1305: -> L1313 THEN GO TO LMOD2 L 1306: LMOD4 A - C -> C[WP] L1307: -> L1317 IF NO CARRY GO TO LTB3 L 1310: 1 1 LMIN 0-> C[WP] L 1311: -> L1317 IF NO CARRY GO TO LTB3 L 1312: -> L 1317 GO TO LTB3 L 1313: LMOD2 A+ C -> C[WP] L 1314: -> L 1317 IF NO CARRY GO TO LTB3 L 1315: LMAX 0-> C[WP] L 1316: 0 - C - 1 -> C[WP] L 1317: 1 LTB3 8 -> P L1320: 1 1 DATA OUTPUT L1373: 1 1 1 1 1 1 -> L1303 GO TO LMOD1

The Synergistic Combination of an Oscilloscope and a Microprocessor 29 The connection requirements are minimal with this chip set since only 13 lines are required for all 40 keycode inputs. Large word length This is one of the key features to the serial microprocessor. The word length is 56 bits (14 digits) and one instruction can work on the whole word or a variety of parts of the word; e.g., exponent only. Therefore, a large number of control functions as well as data can be output to the oscilloscope in only one word time, thus resulting in an efficient transfer of control and data. BCD arithmetic This advantage may not be obvious immediately. However, in an application where decimal information is the desired output, it means that software manipulation is very efficient because no code conversions are necessary. In the Model 1722A, the DAC, described in the block diagram discussion, is a BCD DAC. Therefore when the manipulation of data is complete, it can be transferred directly. The increment/ decrement algorithm demonstrates this in Figure 5 and Table III. Here, the appropriate digit is incremented by 1 and outputted directly with no further code conversions necessary. Serial interface In any system that has limitations on space and weight, as in instrumentation, any reduction in parts count and/ or cabling is a significant advantage. The serial microprocessor provides an interface that requires few bus lines with the ability to provide simple remote storage with shift registers. The serial I/O also reduces the hardware requirement. No RAM required The serial nature of the chip set allowed shift registers to be designed into the arithmetic and register circuit. These are used to store intermediate calculations. In other microprocessors, RAM is required for this function. Again, the volume and number of interconnections are minimized with use of this microprocessor. Large ROM space available This is an important feature. In an oscilloscope, there are many controls on the front panel as well as many possible measurement modes as we discussed earlier. Since many of them are interrelated, using one front-panel control may have implications to others. The availability of large ROM space allows programs to be written that take these interrelationships into account. Instruction set This is probably the most important consideration. There is no advantage in having a higher-speed parallel microprocessor as a controller if th~ basic instruction set is limited, and only minor manipulation of data can be performed. This implies that many word-times would be required to perform the more complicated functions. Even though the HP-35 chip set is serial and has a wordtime of 280 J,LS, the instruction set is so powerful that one instruction can change the entire nature of the next word. In many cases, less time is required to perform basic functions with the HP-35 microprocessor than with competitive parallel processors. For example, a six-digit add requires one ROM state and takes 280 J,LS. Other price competitive microprocessors require anywhere from 5 to 20 ROM states and can take as long as 800 J,LS. This instruction set includes a very complete group of branching instructions which allows subroutines to be easily written. Software and editing As in any processor-based system, the need to write and edit software easily is important. The HP-35 microprocessor compilers are written in such a way that single step and dynamic debugging are possible. ALGORITHMS USED IN THE MODEL 1722A This section describes in considerable detail three of the algorithms used in the Model 1722A. These three were picked to demonstrate the power of the instruction set, the mathematics, the time base encoding scheme and the efficiency of the data transfer algorithm. They also demonstrate the overall efficiency of the use of ROM states. Time base encoding The requirement here is to encode nine time base settings and four exponent values into ROM addresses. This is easily accomplished since the keyboard scanning technique implemented in the C & T chip accepts a keycode entry and uses it as the next address on the IA line (see Figure 3). Specifically, when the Model 1722A program reaches the point where the time base setting needs to be interrogated, an instruction is generated on IS (Figure 3) that is decoded by the I/O control. The I/O control then enables that part of the keyboard that is monitoring the time base switch setting. The input interface (Figure 3) generates a keycode from which the C & T generates the next address. The detailed algorithm is shown in Figure 4 and Table II. The important point here is that only 33 ROM states are needed to encode the 9 time base settings and 10 are

30 National Computer Conference, 1975 TABLE IV-Program Listing of Math and Display Algorithm, for the Time Interval Mode of the 1722A ROM ROM ROM Labels Program Statement Address Code Subroutine Address L0160: LAEC O->C[X] L0161: A+C->C[X] L0162: A EXCHANGE C[WP] L0163: RETURN L0267: LSL04 IFS10#1 L0270: ->L0273 THEN GO TO LSCAO L0273: LSCAO 8->P L0274: 1 1 O->C[WP] L0275 1 1 ->L160 LSCA1 JSBLAEC L0276: 1 1 1 O->C[P] L0277: 1 1 1 LSCA2 O->C[X] L0300: 1 1 1 A+C->A[WP] L0301: 1 CEXCHANGEM L0302: C-1->C[P] L0303: IFC[P]=O L0304: 1 ->L0307 THEN GO TO LSCA3 L0305: 1 CEXCHANGEM L0306: 1 ->L0277 GOTOLSCA2 L0307: LSCA3 IFS1 #1 L0310: ->L0325 THEN GO TO L TB4 L0321: LNEXP SHIFT RIGHT C[X] L0322: 1 1 O->C[XS] L0323: 1 1 O-C-1->C[XS] L0324: 1 RETURN L0325: 1 1 LTB4 O->C[S] L0326: 1 1 IFS2#1 L0327: 1 1 ->L0331 THEN GO TO LTB5 L0330: 1 1 ->L0374 GOTOLlNV3 L0331: 1 1 ->L0321 LTB5 JSBLNEXP L0332: 1 1 LDISP 8->P L0333: 1 1 1 1 1 1 A EXCHANGE C[S] L0334: 1 1 1 1 1 1 A EXCHANGE C[X] L0335: 1 1 1 O->C[S] L0336: 1 1 O->C[WP] L0337: DISPLAY OFF L0340: 1 1 B EXCHANGE C[W] L0341: 1 1 SHIFT LEFT A[M] L0342: 1 1 SHIFT LEFT A[M] L0343: 1 1 SHIFT LEFT A[M] L0344: 1 1 SHIFT LEFT A[M] L0345: LDSP2 DISPLAYTOGGLE L0373: 1 1 1 1 ->L0267 GOTOLSL04 L1325: 1 1 1 1 DOWN ROTATE L1326: 1 1 1 1 DOWN ROTATE L1327: 1 1 1 1 DOWN ROTATE L1330: NO OPERATION L1331: 1 1 1 7->P L1332: 1 1 1 1 O->C[X] L1333: 1 1 1 1 1 A+C->C[X] L1334: 1 1 1 A EXCHANGE C[WP] L1335: 1 1 1 C->A[WP] L1336: 1 1 1 LMOD5 IFC[P]=O L1337: 1 1 1 ->L1341 THEN GO TO LMOD6 L1340: 1 1 1 ->L 1372 GOTOLSCAO L1372 - > L0373 LSCAO SELECT ROMO

The Synergistic Combination of an Oscilloscope and a Microprocessor 31 Store Last LlT Value L1325 needed to encode the time base exponent values. This results in extremely efficient use of ROM states. These 43 ROM states have encoded and stored the multipliers, the position of the decimal point, and the exponent value, in approximately 5 ms. Yes ~-- C(P) = 0 Yes S10 = 1 n=o A=O Data output algorithm The requirement here is that the increment/ decrement control be encoded, the appropriate corrections be made to the data, and the data outputed to the DAC (see Figure 3). Two pieces of information need to be encoded. They are (1) should the data be increased or decreased, and (2) at what rate? The first is done starting at address L0125, the second at L0174. Once this is accomplished the appr~ priate mathematics takes place at address L1306 or L1313 and the new value outputed at L1320. See Figure 5 and Table III. Thus, the entire encoding, mathematical manipulation, and data output is accomplished with 58 ROM states in approximately 10 ms. A...- A+LlT Time internal display algorithm This algorithm takes the new LlT value computed in Figure 5 and performs the appropriate mathematical scaling determined from the scaling algorithm in Figure 4. This scaled value is then shifted into the display. See Figure 6 and Table IV. The most important thing here is that 5-digit multiplication (L0277) takes place with 8 ROM states in less than 12 ms. >0... 1/LlT - S2 = 1 Set Sign of Exponent to (-) Output New Display L0332 OTHER CURRENT MICROPROCESSOR APPLICATIONS IN INSTRUMENTATION There are many examples of ROM-based control systems in instrumentation today (see references). Some of them, such as, the HP Model 1722A 1 oscilloscope, HP Model 3380Al Integrator, and the Tektronix DP07, use microprocessor chip-sets found more commonly in hand held calculators, point-of-sale terminals, etc. The remaining instruments, such as, the HP Model 3490A 4 voltmeter and the HP Model 3330A3 synthesizer, -as well as many more, use dedicated, ROM-based microcontrollers designed with off the shelf logic. In either case, the trend toward ROM-based controllers in instrumentation is definite. CONCLUSION Figure 6-Mathematics and display output algorithm for the time interval mode of the 1722A It is becoming obvious in almost all forms of electrical design that the microprocessor can be an invaluable asset, as it allows "smart" circuits to be developed. The HP Model 1722A is one example of this. The microprocessor

32 National Computer Conference, 1975 will provide the basis for many exciting designs in the future. We at Hewlett-Packard are dedicated to solving customer measurement needs and the microprocessor will playa large role in this. REFERENCES 1. Fischer, W. and W. Risley, "Improved Accuracy and Convenience in Oscilloscope Timing and Voltage Measurements," Hewlett-Packard Journal, December 1974. 2. Whitney, T., France Rode and Chung Tung, "The 'Powerful Pocketful': An Electronic Calculator Challenges the Slide Rule," Hewlett Packard Journal, June 1972. 3. Kingsford-Smith, C., "The Incremental Sweep Generator-Point by Point Accuracy with Swept-Frequency Convenience," Hewlett Packard Journal, July 1972. 4. Thompson, L., "A New Five-Digit Multimeter That Can Test Itself," Hewlett-Packard Journal, August 1972. 5. Oliver, B. M., "Looking Ahead," IEEE Spectrum, November 1974. 6. Allan, R., "New Measurement Capabilities," IEEE Spectrum, November 1974. 7. Saba, Mona and Jack Grimes, "Microprocessors: A Component for all Seasons," 1974 Wescon Professional Program, The Microprocessor Revolution, Part II.