INTRODUCTIONTO LSI

MICROPROCESSORDEVELOPMENTS

A. 0. Williman, Rockwell InternationalH. J. Jelinek, Consultant

Introduction

In its constant endeavor to increase the number offunctions per semiconductor device, the semicon-ductor industry has focused continual effort on develop-ing new semiconductor processes and photolitho-graphic technologies and on compressing smallergeometries onto increasingly larger silicon chip areas.The result is that the number of functions (componentsper chip) is approximately doubling every year whilethe cost per function is decreasing. A byproduct ofthese improvements is increased system reliability.By increasing chip complexity above a few hundredgates, generally referred to as large-scale integration,the capability of economically producing new devicesand systems for new applications is being realized.In this paper, a relatively new class of devices

will be described which have been made possibleby these advances in semiconductor processingtechnology. This class of devices, microprocessors,may be described generally as the application ofLSI to general-purpose information processing.Microprocessors are only five years old but aremature in the sense that there are over 25designs on the market. In this paper, we willtry to briefly explain (1) what microprocessors areand what is available, (2) what microcomputers areand what is available, (3) who uses microprocessors,(4) user considerations, (5) technologies used, and(6) some projections about the future of micro-processor systems.

What Are Microprocessors andWhat's Available?

The definition of what characteristics qualify anLSI device as a microprocessor varies considerably.Table 1 gives a definition based on complexitycharacteristics. It divides the microprocessor hier-

archy into three levels: the microprocessor, the micro-computer, and the microcomputer system. Lewin'has defined a microprocessor as "a monolithic (one-chip) processor." However, new architectural con-cepts demand a somewhat broader classificationscheme. Table 2 provides another approach to definingmicroprocessors. It classifies them functionally asbeing between a calculator and a minicomputer.The same table compares microprocessors with cal-culators and minicomputers in terms of several

Table 1. Microprocessor definition

* MICROPROCESSOR2- CONSISTS OF LSI CIRCUIT OR SET OF

CIRCUITS- CAPABLE OF PROCESSING LOGICALAND ARITHMETIC DATA UNDER PRO-GRAM CONTROL OR IN PARALLEL MODE

, (QTY/YR < 10,000 STANDARD CIRCUITS)- (QTY/YR > 10,000 CUSTOM ClRCU ITS)

* MICROCOMPUTER- CONSISTS OF MICROPROCESSORS(ASSEMBLED ON BOARD) PLUS MEMORYAND I/O RECEIVER/DRIVERS

- (QTY/YR - 10-4 1000)

* MICROCOMPUTER SYSTEM- CONSISTS OF MICROCOMPUTER (BOARDMOUNTED IN CHASSIS) PLUS APPLICA-TION MEMORY, POWER SUPPLIES,CONTROL PANEL, AND PERIPHERALS(QTY/YR - 1 --+10)

COMPUTER

aSpecial Tutorial,

34

Table 2. Microprocessor characteristics

INCREASING SPEED, FLEXIBILITY, COMPUTING POWER

| CALCULATOR I|- MICROPROCESSOR |-| MINICOMPUTER |

WORD LENGTH (BITS)SERIAUPARALLELMICROINSTRUCTIONCYCLE TIME

INSTRUCTIONSINPUT/OUTPUT

BIT MANIPULATIONINTERRUPTDIRECT MEMORY ACCESS

MULTI CHIPMICROPROGRAMMABLEARITHMETIC

1, 4SERIAL4-40 pSEC

20-40KEYBOARD DISPLAY,PRINTERNONODEDICATED TOKEYBOARD

SOMENOBCD

4,8,12,... 16PARALLEL500 NSEC-10 pSEC

30-100FLEXIBLE, SLOW

YESSOMESOME

YESSOMEBINARY AND BCD

8, 12, 1-6, 32PARALLEL200 NSEC-1 pSEC

70-200FLEXIBLE, FAST

YESYESUSUALLY

TTL, OR TTUMOSSOMEBINARY AND BCD

Figure 1. Typical CPU

June 1976 35

Aft

rNREQO SIK

FULL

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SVRST RALU CSHOX

CYOV1 (12-15)

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DATAX NCBXSININX (0)-(3) (0)-(3)

INPUT BYTE SIGN (1)

SIGN BIT & OTHER SELECTED R-BUS BITS

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JUMPMULTIPLEXER MEMORY T7

INT DATA 7

NTEN ISELX

SVRSTFLAG ENABLE

RD FLAG U

WR LATCHES

ID FLAG DATA

OD_

LDAR

Anl)RFI;IARI FIATC

IDATA BUS (16)

tVGG

DAT(8)(11)T7-T8

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(4)

DATA (12) (15)

(4)

-IT

_V---t DELAYEDREAD FLAG

VGG T7-T8BZE S

MULTIPLER 10

MULTIPLEXERI

CONTROLBUS(4)

(1)

(4)

T2-T3

CH-

Figure 2. Block diagram of typical bit-slice microcomputer (National IMP)

characteristics such as word length, number ofinstructions, etc. Generally, microprocessor capabilityis progressing toward the minicomputer. This isparticularly true for several of the bit-slice micro-processor organizations.

Architectures. Microprocessors can be dividedinto two general categories: one-chip CPU's andmultichip CPU's. The one-chip CPU's contain theprogram counter, instruction decode and control,ALU, and general-purpose stack registers-all on

36

one chip. They are typically 4 or 8 data bitswide, although several 16-bit configurations areavailable. Examples of the one-chip CPU organiza-tion are the Intel 4040 (4-bit) and 8080 (8-bit), and theRockwell Microelectronics PPS-4 (4-bit) and PPS-8(8-bit) systems. Multichip organizations generallyconsist of several bit-slice register and ALU chips(RALU) and a control read-only memory (CROM)which handles the instruction decode and control.The CROM provides flexible instruction decode andflexible instruction set definition not offered by organi-

COMPUTER

RALU(8-11)

RALU(4-7)

RALU(0-3)

HOCSHX DIX DIX

JUMPCONDITION

NCB'

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.40-

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zations with hardwired instruction decode logic. TheIntel 3001/3002 and the National Semiconductor IMPseries are examples of bit-slice architecture. Blockdiagrams of the two primary architectures are shownin Figures 1 and 2 respectively.Tables 3, 4, and 5 summarize the characteristics

of some of the microprocessors currently on themarket.4'5 Table 3 is a breakdown of existing pro-duction-proven microprocessors from Intel, NationalSemiconductor, Rockwell Microelectronics, andMotorola. The 4-bit processors (Intel 4004 andRockwell PPS-4) were the first devices on themarket, but the 8-bit is becoming a predominantproduct.

Generally, manufacturers have developed familiesof chips which include memory and I/O to make upmicroprocessor systems. It is very desirable thatcompatible chips be available to simplify the systemdesign.Estimates of currently available CPU prices for the

major companies are given in Table 3. These prices

June 1976

have shown a continual downward trend. Also identifiedin this table is the type of software support (assemblers,simulators, and emulators) generally available. Theonly microprocessor program compiler presentlyavailable is the PLM compiler from Intel.Table 4 lists some of the relatively new micro-

processors entering the market and their prices,where known. These devices predominantly have 8-bit word length devices, compatible memories (ROMand RAM), and in some cases I/O chips. Also givenin this table are the estimated availability datesfor these processors.Table 5 shows some additional processors which,

with the exception of the Raytheon RP-16, are bit-slice organization with fast cycle times. These fastcycle times are made possible through the use of semi-conductor technologies (which are discussed in detailin a later section), such as Schottky TTL (transistor-transistor logic) and NMOS (N-channel metal oxidesemiconductor). Texas Instruments has an 12L(integrated injection logic) bit-slice device, theSBP 0400, which has aroused the interest of theengineering world. F2L is a bipolar technology whichexhibits relatively good speed characteristics at MOSdensities and power dissipation. These three tablespresent information which demonstrates that a largenumber of microprocessors are available with avariety of characteristics. This wide choice makesit very difficult for a user to select a microprocessorwhich will be the optimum one for his application.Some user considerations are disclosed in a latersection.

What are Microcomputers, andWhat's Available?

As shown in Table 1, a microcomputer2'3 consistsof the elemental LSI components required to realizea digital computer. The components, mounted on aprinted circuit board, are the processor, minimummemory, and some limited I/O circuitry.A microcomputer system contains a more developed

microcomputer plus the supporting power supplies,control panels, etc., which present the user with acapability nearly equal to that of a minicomputer.The cost and-today-the performance of such aconfiguration will be under that of a minicomputer.The microcomputer system may be applied in a dataprocessing application. However, it is more likely tobe used in performing the multiple requirementsrelated to designing a microprocessor-oriented systenLThese requirements are ROM program developmentand checkout, system emulation, and testing. Itmay also be used directly in a controller applica-tion or as a minicomputer replacement.For reference, Table 1 shows quantities of systems

per year that are cost-effective for a given level ofintegration.4 This may be used as a guideline todetermine the volume necessary to develop a parti-cular system.Figure 3 shows a typical system block diagram

for a microcomputer/microcomputer system. Thesystem structure and availability of the compatible"support" circuits shown in the figure are extremely

37

Table 3. Existing general purpose microprocessors

important. If compatible I/O devices and memoriesare not available, a significant number of standardcomponents may be required to mechanize a parti-cular requirement..6 This lack of support circuitscan make the use of a microprocessor less attractiveand perhaps less cost-effective than an equivalentTTL system. As shown in Figure 3, special LSIdevices are used for significant numbers of I/Ofunctions. It is important that the microprocessoralso be able to use standard low-cost read/writememories, ROMs, and PROMs since these can havea pronounced effect on the total microcomputer cost.For the small-quantity user, several companies

are now offering total microcomputers. As shown inTable 6,2,3 4-, 8-, and 16-bit microcomputers areon the market using available devices. Approxi-mately 50% of the microcomputer configurationscurrently in use have 8-bit word lengths. There is,

38

however, a move toward more 16-bit word lengthmachines. The ultimate limiting factor on single-chipprocessor word length is package pin requirementsand package power dissipation.For those applications requiring longer word

lengths, the bit-slice devices may be assembled intoa computer structure having word lengths greaterthan 16 bits. However, the technology used in thebit-slice must be capable of driving large inter-face loads so that the processing speed is notseverely cut. In addition, look-ahead circuits willprobably be required in the ALU section to avoidthe slowdown inherent in a ripple carry approach.Fairchild Semiconductor introduced a series ofdevices called "Macrologic" in 1975 that are fabri-cated in the low-power Schottky technology. Thesedevices may be assembled into a printed circuitboard and interconnected to form a computer of the

COMPUTER

Who Uses Microprocessors?

Surveys have indicated that microprocessors areused in a broad range of application areas and thatno one area, if one excludes calculators, holds themajority share. 'These applications include com-ponent testers, printers, point-of-sale terminals,computers (terminals and peripheral controllers),industrial controllers, aerospace, office equipment,etc. In summary, there is a broad base of usagebut not many large users.

Development Considerations. Generally, designengineers specify not only whether a microprocessorwill be used but also which specific one will be employed.It ordinarily takes six months from the start of aprogram to an operating prototype. The primaryfunction of the microprocessor is to replace hard-wired logic in current and new applications. Applica-tions in which the microprocessor can replace be-tween 50 and 250 TTL devices are probably cost-effective. An advantage of using a microprocessorsystem rather than TTL is that the microprocessorversion permits changes to be made in firmware(ROM programs) and permits modularity of I/Othrough I/O channels. This flexibility helps delayproduct obsolescence and permits augmentation ofthe first product. The firmware approach also helpsreduce rework time in cases of functional changesor changes necessitated from errors found at check-out. Other advantages of microprocessor-imple-mented systems are smaller size and better reliabilitythan discrete component type mechanizations. Prob-ably one of the major factors influencing micro-processor utilization is that they are state of theart and design engineers are interested in them!

User Considerations8'9

desired word length. The complexity of these devicesis roughly 250 gates/chip. Consequently, it would-take 6 to 10 of these devices to implement an8-bit processor unit. The resulting processor will befaster than the fastest NMOS microprocessorspresently available.

In smaller systems, the cost of the microcom-puter is approximately 15% CPU, 20% I/O, and65% memory. These percentages can vary significantlydepending upon the specific application. It is ap-parent, however, that the memory is a significantpercentage of the microcomputer cost. The quantityof memory required to implement a given applica-tion will have a large cost impact. Standard semi-conductor R/WM's, ROMs, and PROMs are theprimary memories utilized. The availability of thesememories is improving and costs are continuallydecreasing.

In the selection of a microprocessor, the useris faced with understanding and comparing a myriadof parameters (see Table 7). The importance ofthese parameters varies and is dependent on thespecific application.

Cost. The cost comparison of microprocessors isoften based on the relative costs of CPU and memorydevices. As pointed out previously, the cost shouldbe based on total system costs, because differentmicroprocessors may require additional peripheralcircuitry or memory due to speed requirements,I/O device availability, or architectural configuration.

Availability. Availability was a predominant de-cision factor a few years ago. It is still a con-sideration when anticipating the use of advanceddevices. However, increased production and secondsourcing are changing the picture in favor of theuser. The availability of production as well assample quantities should be investigated beforecommitting to a particular vendor.

June 1976 39

Table 4. New microprocessors

Table 5. Other microprocessors

ADVANCED MONOLITHIC TEXAS SCIENTIFICMICRO- INTEL MEMORIES RAYTHEON INSTRU. MICRO- TRANSITRON

PARAMETER DEVICES 2901 3001/3002 6701 RP-16 SBPO400 SYSTEMS 300 TMC(1601)

WORD LENGTH 4 2 4 16 4 8 4

TECHNOLOGY TTL TTL TTL ECL 12L TTL-S TTL-S

CYCLETIME(pS) 105NSECMIN.165 .150 0.1 1.0 250NSEC ?

NUMBEROF 105 MIN. 40 36 38 459 8 ?INSTRUCTIONS p INSTRUC. p INSTRUC.

POWER SUPPLY 5V 5V 5V 5V 0.85 TO 4V 5V ?

CPU 4-BIT SLICE, 2-BIT SLICE, 4-BIT SLICE, 48-PIN, 4-BIT SLICE, 50-PIN SINGLE 4-BIT SLICE,CONFIGURATION 40 PIN 28 PIN 40 PIN 7CHIPS 40 PIN CHIP 40-PIN

CHIP FAMILY SEQUENCER, CARRY BUFFER, RAM, ROM, I/OI/O, INTER- INTERRUPT,RUPT, CARRY PROM

CPU PRICE $21 (100 3001:$35 $95(100) $187(1-14)AND OVER) (1-24) $90 (100)

AVAILABILITY NOW 3Q74, 1Q74 2Q75 4Q74 OFF-THE- 1Q756 WEEKS SHELF

COMMENTS MICRO- 2NDSOURCE: PLANNING 2ND SOURCE: NEWAVAIL-PROGRAM- SIGNETICS PLA FOR p SIGNETICS ABILITY 1976MABLE PROGRAM

COMPUTER40

CLOCK A(TTL)I GENERATORA(TL

PARALLEL TD1,GPKD,t t TTL I/O CHANNELS CONTR

B 16 DATA, 4 CONTROL SERIAL CONTROLLER,LINES PER DEVICE 1/0 CHANNEL

Figure 3.PPS-8 Microcomputersystem block diagram

PROGRAM/CONSTANT READ/WRITE TTL DISCRETESTORAGE STORAGE 12 INPUTS/DEVICE AND

12 OUTPUTS/DEVICE

June 1976 41

Table 7. User considerations

4 BITINTEL 4004INTELPRO-LOGAPPLIED COMPUTING TECHNOLOGY

ROCKWELL PPS 4APPLIED COMPUTING TECHNOLOGY

TDY-52ATELEDYNE CORPORATION

8 BITINTEL 8008INTEL CORPORATIONPROLOG CORPORATIONDIGITAL EQUIPMENT CORPORATIONCONTROL LOGICPROCESS COMPUTER SYSTEMSR2E-U.S. REP: 3MICROSYSTEMS INTERNATIONALMARTIN RESEARCH

INTEL 8080INTEL CORPORATION -80/10CONTROL LOGICPROCESS COMPUTER SYSTEMSR2EMITS ALTAIR 8800MYCRO-TEK INC. MT8080COMSTAR DIV. WARNER SWASEY-INTEL DEVICES

IMS ASSOCIATES- I MSAI 8080INFORMATION CONTROL CORP.-ABACUS MICROSYSTEM

ELECTIRONIC MEMORIES ANDMAGNETICS-SYSTEM 80

MONOLITHIC MICROCOMPUTER-8080+MARTIN RESEARCHRAMTEK- MM80

IMP8CNATIONAL SEMICONDUCTOR

MOTOROLA M6800MOTOROLAMITS ALTAIR 6800SPHERE CORPORATION

MOS TECHNOLOGY 6502EBKA INDUSTRIESMOS TECHNOLOGY-KIM-1 (USES 6502 CHIP)

16-BITIMP-16-NATIONAL SEMICONDUCTORTDY-52B-TELEDYN E(USES NATIONAL IMP-16 CHIPS)

NAKED MINI/LSI-COMPUTER AUTOMATIONHAMILTON/AVNET PACER (USES NATIONAL"PACE" CHIP)

TEXAS INSTRUMENTS-990/4(USES TMS 9900 CHIP)

* COST

* AVAILABILITY

* SOFTWARE/APPLICATIONSSUPPORT/DOCUMENTATION

* MICROPROCESSOR ARCHITECTUREWORD SIZE (DATA/INSTRUCTION)

- QUALITY OF INSTRUCTION SETREGISTER ORGANIZATION ANDCOMMUNICATIONINTERRUPTS1/0-MEMORIES-COST/SIZE/BUSSTRUCTURE/PROMSSPEEDDMA

* MICROPROCESSOR PHYSICAL STRUCTURE- PACKAGE COUNT (INCLUDING

PERIPHERAL CIRCUITS)PIN COUNTPOWER SUPPLIES REQUIREDPOWER CONSUMPTIONCHIPS VS BOARD VS MICROCOMPUTERRELIABILITY

* SECOND SOURCE

* TESTING

Programming Aids. Another very importantaspect of microprocessor selection is the availa-bility of programming aids. Table 8 is a list oftypes of user aids which should be availablefor microprocessor firmware program development.In general, the increased utilization of microproces-sors has moved the implementation of systems froma logic/design hardware domain to a programming/hardware (firmware) domain. Applications arenormally programmed in an assembly languageusing available assemblers. Once it is assembled,the program is run on a simulator to determinecompatibility with the desired microprocessor systemfunction. However, short programs may be codeddirectly using well designed code sheets. For thebit slice organization, instruction sets are normallymicroprogrammed, although a "standard" set isavailable if desired. The application programs aresubsequently macroprogrammed using an as-sembler and simulator. If the macroinstructions areunique, the assembler and simulator have to begenerated for the specific instruction set. Anemulator is often used for checking out I/O inter-

Table 6. Microcomputers

Table 8. Programming aids

ASSEMBLER MNEMONIC CODEMACHINE LANGUAGE

- RESIDENT-DIRECT MNEMONICINPUT

CROSS ASSEMBLER-ASSEMBLEON LARGE COMPUTER

SIMULATORS SIMULATES CPU FOR DE-DEBUGGING PROGRAMS

- GENERALLY ON LARGECOMPUTER

EMULATOR CPU HARDWARE WITH RAMREPLACING ROM

FORPROGRAM DEBUG

COMPILER - HIGHER LEVEL LANGUAGERUNS ON LARGE COMPUTERFASTER PROGRAMDEVELOPMENT

face and critical timing paths during the programdebug phase.Only one high-level language, Intel's PLM com-

piler, is presently being offered as a programmingaid. There has been some work" 10'12 on tradeoffsrelative to the use of compilers vs. assemblylanguage. This tradeoff is made among the numberof equivalent machine level instructions generatedper compiler instruction, cost of memory, and thecost of checkout and documentation.

Program Checkout.'3 The cost of checkout anddocumentation tends to be proportional to thenumber of instructions generated whether they becompiler or assembly instructions. Therefore, a com-

piler will have less of these associated costs sincethe number of compiler instructions for a givenapplication will be less than the number of corres-

ponding assembly instructions. The programming(coding) costs will be less with the compiler becausefewer instructions are needed. Offsetting the costredu6tions made possible by using a compiler is thefact that compilers are less efficient in the utiliza-tion of memory than programmers using assemblers.There is, therefore, a tradeoff between reduction infixed costs of programming and the recurring costof additional memory. This trade-off indicates that a

higher-order language is cost-effective where fixedprogramming costs dominate. Assembly languageprogramming should be used where recurring costsdominate (a large number of production systems).Some studies 8,9 have indicated that (a) for a smallmicrocomputer program of about 4000 bytes, a com-

piler is cost-effective if production is less than 10systems; (b) an assembly language approach is morecost-effective if production is greater than about 100

June 1976

units; and (c) between 10 and 100 systems, theapproach depends upon the specific application.Software cost and schedule can have a significantimpact on a system and the availability of efficient,checked-out, and maintained software aids is neces-sary to ensure timely development of software ina system design.

Architectural Considerations. As shown inprevious tables, several microprocessor architecturesare available on the market. The most desirablemicroprocessor architecture for a given applicationcan best be determined by comparing requiredperformance with the microprocessor functional andelectrical specifications. The final selection of aparticular architecture is often determined by theability of that configuration to meet speed re-quirements (clock rate, word size, instruction set,registers, interrupts, I/O, etc.), efficiency of memoryutilization (word size, instruction set, registers, I/O,DMA, etc.), and other factors such as availability.

Physical Structure. The microprocessor physicalstructure (package type/pin count) will directly in-fluence system characteristics and cost and cannormally be assessed more directly than microproces-sor- architecture. The package cotnt translates intonumbers of boards required. Pin count definesdata word length and memory addressing capabili-ties. Some of the newer processors have gone tolarger numbers of pins (typically 40) to providemore effective b'ussing (and, therefore, speed).The modularity level at which the microproces-

sor is purchased should be considered. As alreadyshown in Table 1, for large production it is moreeffective to purchase devices, but for a few pro-duction systems it may be more effective to buyat the board or microcomputer level.The reliability of a P- or N-channel MOS LSI

device has been established as being a slightlyhigher failure rate than TTL SSI devices, butsince there'are fewer LSI devices required for agiven system and since LSI permits far fewerconnections (which are predominant failure modesin systems), you end up with a much highersystem reliability.

Second Sourcing. Second sourcing of micro-processors has not been adequate in the past, butthere are now second sources for most of thestandard microprocessors- e.g., AMI/Motorola/,RockweWllNational, FairchildlMostekl, AMD/MotorolalRaytheon, Intel/AMD/TI, as shown on Tables 3, 4,and 5.

Testing. Testing is a significant consideration inmicroprocessor selection. Some of the factors whichshould be considered are (1) receiving inspectiontechniques, (2) whether testing should be done atthe device level versus system level, (3) how muchat each level, (4) software versus hardware testing,(5) diagnostic routine availability or generation,etc. Testing can be an expensive and time-consumingfactor in the selection of microprocessors.

43

PMOS

NMOS

Figure 4. Semiconductor technologies

Semiconductor Technologies Used14,15'16

As previously shown on Tables 3, 4, and 5,several production semiconductor technologies areused for microprocessors; these are summarized inFigure 4. The technologies can be categorized intotwo basic divisions according to substrate materialused-i.e., non-insulating silicon, and an insulatingsubstrate (where silicon-on-sapphire is the primarycontender). Both bipolar and MOS transistors canbe produced in bulk silicon; however, only MOSFETs(field effect transistors which are surface devices)can be produced on SOS due to large bulk leakageexhibited in this substrate technology.

Bipolar device structures are determined byapproaches used to isolate the individual transistors.In the epicollector approach, an epitaxial layer underthe device is connected to the collector diffusionwhich isolates the periphery around the device.The 3D approach uses a diffusion for isolating thedevice. Isoplanar technology uses silicon dioxide forisolation. Bipolar LSI devices use either the epicol-lector or isoplanar approaches since they providedenser structures. Several circuit forms are avail-able in each basic structure as listed in Figure 4.T2L Schottky (T2LS) and emitter-coupled logic

(ECL) are used in some of the faster bit-slice

44

microprocessor approaches; however, they consumea significant amount of power. 12L and comple-mentary coincident current logic (C3L) are newcircuit techniques which have very low gate delay-power products and therefore overcome the powerdissipation/chip limitations.The MOSFET is a basic MOS structure used

for logic and memories. It can take several forms:P-channel, N-channel, complementary, and metalnitride oxide semiconductor (MNOS). P-channel isthe first standard MOS process and was used inthe first microprocessors and many production de-vices. The N-channel process has higher chargecarrier mobility (speed) and lower threshold voltage(permitting higher density). It has become thestandard process for MOS memories and is nowbeing used for logic as well. CMOS (complementaryMOS) is used for two microprocessors (RCA COS-MAC and Intersil 6100) and has an advantage oflow power but has the disadvantage of low densitydue to isolation requirements between N-and P-channel transistors.The insulating substrate in silicon-on-sapphire

provides less capacitance and inherent device isola-tion, and these features in turn provide speedand drive density advantages. SOS technology hasbeen in development for several years and is at

COMPUTER

SUBSTRATEMATERIAL

BASICDEVICE TYPE

BASICDEVICESTRUCTURES

CIRCUITFORMS

Table 9. Semiconductor processes

PMOS NMOS VMOS CMOS SOS BIPOLAR 12LCMOS TTL

SPEED(1 = FASTEST) 6. 5 2 3 2 4

DENSITY (CIRCUIT LAYOUT) 2 (i) 3 2 4 2(1 = MOST DENSE)

POWER (1 = LEAST) 3 2 0 0 4

EXPERIENCE(1 = MOST) 2 3 6 4 5 Q 6

PROCESS COMPLEXITY 2 2 4 4 3 3(1 = LEAST)

* POWER IS A FUNCTION OF SPEED

the point of commercial production for MSI anda few LSI devices in CMOS/SOS. An early attempt wasmade to develop an N-channel-on-SOS microproces-sor chip, but it failed due to process yield prob-lems17 (related primarily to controlling diffused pull-up resistors). Some companies are continuing todevelop a CMOS/SOS process for LSI processorsbecause of its speed and power advantages.Two developments in the MOS arena offer charac-

teristics which make it possible to achieve improve-ments in speed and density. The V-MOS approachpresents a technique for obtaining short transistorchannel lengths by using the selective etchingcharacteristics of certain materials in conjunctionwith controlled diffusions. The resulting V shapedtransistor is vertical and occupies an area lessthan 30 microns square. The D-MOS technologyhas been around for several years but has beenapplied to LSI devices only recently. It too yieldsdevices with very short (1 micron) channels and pro-vides attendant improvement in device delay. Inaddition to these fundamental technology improve-ments, progress has been made in NMOS in thearea ofRAM cell size and in multilevel interconnect.The so-called double-polysilicon approach is beingemployed in some of the new 16K RAM designsand may be expected to find its way into newmicroprocessor chip designs.

It is very difficult to present a comprehensivegeneralized evaluation of technologies in a shortpaper because the effectiveness of each processapplication is heavily dependent upon the specificcircuit design and layout. However, Table 9 is anattempt to show relative process advantages in acompact summary fashion. The processes are rankednumerically for a given parameter. The attempt ismade in this table to qualify how much betterone process is over another in a particular cate-gory. The processes which are first in each cate-gory are circled. In some cases, where the pro-

cesses are close together, more than one may havethe same number. It may be noted that each pro-cess is "first" in some category-a fact that shouldmake the reader appreciate why no one processdominates in all applications.

COMPUTER ARCHITECTHoneywell's Systems and Research Center has an immediaterequirement for a Computer Architect. This person will provideproject leadership and work as a technical contributor onprojects involving design of hardware and software systemsfor DOD applications.

Desirable qualifications include:

* Project leadership experience or participation in the designof computer SOFTWARE and HARDWARE systems formilitary, telecommunications, or real-time controlapplications.

* Logic design and computer system architecture background.

* Minicomputer programming experience.

* Well developed verbal and written communication skills.

* Advanced technical degree (preferably EE, Computer Science).

We also have a junior level position available for an exceptionallywell-qualified MS or PhD level person.

We offer highly competitive salaries with an excellent benefitsprogram. If you seek the challenge and excitement associatedwith our operation please submit resume in complete confidenceto our Employee Relations Department, R2340:

HONEYWELL INC.Systems and Research Center

2600 Ridgway ParkwayMinneapolis, Minnesota 55413

An Affirmative Action Employer

June 1976 45

What Is the Future of Microprocessors?

Microprocessors have exploded into the electronicsscene rather recently, and there is not much of alearning curve from which the user can benefit.It is apparent that microprocessors are provingcost-effective for a number of applications, and asmore experience is gained their applications willbroaden. The P- and N-channel MOS single chipmicroprocessors will be used for low performancerequirements. The bipolar bit slice, microprogram-mable microprocessors will be used for higher per-formance requirements. The one-chip microprocessorwill have instruction cycle times in the micro-second region, whereas bit-slice processors will have100- to 300-nanosecond instruction cycle times.There will be more I/O oriented devices for micro-prqcessors, and microprocessor architecture will beefficient in I/O. There will be a few custom micro-processors in minicomputer emulations. Severaltechnologies will continue to be used. N channelMOS will predominate for one-chip microprocessorsand memories. Bipolar will predominate for thebit-slice high-performance applications. The user isgoing to have a variety of microprocessors tochoose from and a very large compendium ofliterature."' His selection of a particular configura-tion will be dependent upon his ability to tradethese off against inhouse skills and the applica-tion requirements. N

References

1. Morton H. Lewin, "Integrated Microprocessors," IEEETransactions on Circuits and Systems, Vol. CAS-22, No. 7,July 1975, pp. 577-585.

2. Michael Teeher and William Liles, "Microcomputers,"ModemrData, February 1975, pp.49-53.

3. "Microcomputer Scoreboard, " Microcomputer Technique,Inc.

4. "Microprocessor Scoreboard," Microcomputer Technique,Inc.

5. Jerry L. Ogdin, "Microprocessors: The Inevitable Tech-nology," Modem Data, January 1975, pp. 42-47.

6. Jerry L. Ogdin, "Other Microcomputer Chips," ModemData, February 1975, pp. 43-47.

7. "The Microprocessor," EDN, August 1974.

8. Eric Garen, "Applying Microprocessors and Microcom-puters,"Modem Data, February 1975, pp. 54-57.

9. Gregory Fox, "Evaluation of Microprocessor Performancefor Military Systems," IEEE Trans. Circuits and Sys-tems, Vol.7, No.6, April 1975, pp.

46

A. 0. Williman is program manager of ad-vanced microelectronic applications in theAutonetics Division of Rockwell Internation-al. His responsibilities include initiating andmanaging programs related to application ofadvanced technologies such as CCD's andmicroprocessors. Previously, he was directorof calculator development and microprocessordevelopment in the Microelectronic Divisionof Rockwell. In his 16 years with Rockwell,

he has had idditional managerial and engineering assignmentsin computer and systems design and applications. Mr. Wiflimanreceived his BSEE from UCLA in 1952 and his MSMEfrom USC in 1957. He is a member of the IEEE, IEEEComputer Society, and AIAA. He has presented and publishedseveral papers on multiprocessors and multicomputer systems.

H. J. Jelinek is a consultant in the areasof digital systems and microprocessor applica-tions. During 15 years of industrial andacademic experience, he has worked in com-puter-aided design, and digital system designand product testing at Rockwell Internation-al; earlier, while pursuing research work inanalog and digital system diagnosis at theUniversity of Canterbury in Christchurch,New Zealand, he taught courses in circuit

theory, switching theory, and semiconductor physics.A member of the IEEE and the IEEE Computer Society,

Dr. Jelinek served as chairman of the Orange County Chapterof the Computer Society in 1974.

10. Jerry L. Ogdin, "PLM vs Assembly Language," NewLogic Notebook, Vol. 1, No. 4, Dec. 1974.

11. A. 0. Williman, "Software 'Considerations fpr GPS,'"Rockwell International internal letter, May 1975.

12. Jim Gibbons, "When to Use Higher-Level Languagesin Microcomputer-Based Systems" Electronics, August7,1975, pp. 107-111.

13. Douglas A Cassell, "Microcomputer Programming,"Modem Data, January 1975, pp. 49-5 1.

14. A. Scott McPhillips, "Inside Microprocessors," ModemData, January 1975, pp. 37-41.

15. "Solid State,"Electronics, October 17,1974, pp. 138-151.

16. C. M. Hart, A. Slob, and E. J. Wulms, "Bipolar LSItakes a New Direction with Integrated Injection Logic,"Electronics, October 3, 1974, pp. 111-118.

17. Electronic Engineering Times article, July 29, 1974, p. 22.

18. Ann Ward, "LSI Microprocessors and Microcomputers-ABibliography Continued," Computer, January 1976, pp.42-53.

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