Cad System for Ula

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A REMOTE DESIGN STATION FOR CUSTOMER UNCOM MITTED LOGIC ARRAY DESIGNS

Frank R. Ramsay

Ferranti Electronics Limited

A B S T R A C TThe paper describes a low cost remotedesign station that can be installedin customers offices, giving them thefull C.A.D. fa cilities requ ired tospecify, design and verify an Uncommi ttedLogic Array. The designers can enterand check their logic, lay outs and testprograms via this remote station. Accessis then available, via mod em links, tothe main Ferranti C.A.D. facility forrunning of design verifica tion programsetc.The need for such a system came aftermany years experience in handlingcustomer designed circuits.

i. INTRODUCTIONFerranti Electro nics have been produci ngcustomis ed uncommitted logic arrays (ULA)for the last ten years. The initial aimbehind the ULA concept was to produce aquicker more economical route to customintegrated circuit design than the full,all mask, cust om route we had been usingin the sixties. The ULA has succ eededin this area throughout the seventies whenmost of the custom designs were done byF e r r a n t i ' s M i c r o e l e c t r o n i c s D e s i g n C e n t rebased engineers. However, for theeighties, where much more emphasis ofcusto m desig n is to be placed on thecustomer, a new approach is required.Design fa cilities are required in thecustomers laboratories and offices. Todayintegrated circuit design, even for ULA'sis impracticle wi thout access tospecialised design automation softwareand therefor e for the customer to dothis work in his office means the DAsoftw are has to be availa ble in his office.

The aim is that the customers will performthe logic and layout design phase in theirown plant, using the large C.A.D. aidsavailable at the design centre whereappropriate, and then will enter the finallayout into their design station via adrawing reading machine. From here thedata can be plotted and edited beforebeing tran smitted to the design centrefor full design verif icatio n and finallyformatting for the pattern gener ator etc.While mask and prototype devices are beingmanufa ctured the customers can use theirremote design station to generate, debugand verify the device test program.

2. U.L.A. C.A.D. SYSTEM AT THEM I C R O E L E C T R O N I C S D E S I G N C EN T R E

The existing C.A,D. system used by Ferrantiat their Design Cent{ ~consi sts of PDPIIand Appl icon syste ms'-'. A VAX is now beininstalled to improve capacity and per-formance.The syste m has 3 inputs layout, logic andthe test schedu le (Fig i). From these arederived the necessary pattern gen eratortapes and test programs along with theresults of design and interconnectverification etc.

EHECK

AL |CE

FIG I ~ERVIEW OF U.L.A. C.A.D. SYSTEM

Paper 24.2 18th Design Autom ation Conference498 0146.7123/81/0000-0498500.75 1981 IEEE


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The key to this system is that the variousmodule s are all linked and relate to amaste r des ign data base - the logicdiag ram (Fig 2.) This link ensure anautomatic complete ver ificati on of allparts of the design. Implemen tation issuch that it does not restric t thedesigners ability to take full advantageof the ULA's flexi bility.

I LOGICDAGRAM DESGNVERIFICATION_ ~ TESTSCHEDULEVERIFICATION

I fLAYOUT I,- CINTRACELLCHECK INTER cELLJ

F IG 2

AUTO ~ -~ PLACEMENTI- LAYOUT I>[ ROUTNG ILOGIC DIAGRAM DATA BASE LINK

This system is specially tailored forULA work and there are obvious adva ntagesto any remote statio n if it can haveaccess to this verification power etc.

3. EXISTING CUSTOMER DESIGN ROUTESBefore the remote design station conceptcustomers designing their own ULA's couldinterface with the Design Centre in anumber of ways. They could send the pencilinterconnect drawing to the centre fordigitisin g and data processing by Ferrantipersonnel. The main problem with thisapproach was in design verification.Only the designer can solve design problemsand therefore the customers engineer hadto schedu le time to visit Ferr anti tosolve any problems found by the system.Other interfaces were from customers ownC.A.D. systems (Fig 3). The main prob lemwith all these routes was the limitedamount of specialised ULA C.A.D. software

available to the designers on the customersown C.A.D. systems.

APPLICON -,. ) MAGN ETIC ) FERRANTI APPLICONTAPE ARTWORK SYSTEM

C A L M A >M A G N E T I CTAPE . FEHRANTI APPLICO NO T H E R F U L L . M A G N E T I C

C . A .D . S Y S T E M S P T A P E > F E R R A N T I A P P L I C O N

FIG 3 CUSTOM ER INPUTS TO C.A.D. SYSTEM

In the case were the custo mer has anApplicon system they were obviously furtheralong the line than most but would stillneed to purchase the required ULA packagefrom Ferra nti for their intern al use.In the other cases they would be involv edin a considera ble amount of effort totailor th eir own C.A.D. system to ULAdesign and to write the specialisedsoftware needed for a complete ULA designverifica tion system. Even a logic simula-tor probably, the most common electro nicsC.A.D. tool, takes cons idera ble effort totailor to the exact requirements of ULA's.Whichever C.A.D. system the customer usedthey were involved in a major capitalinvestment which required specialisedsupport staff etc. Where ever such asystem was implem ented it was obviouslysuccessful but the investment level isconsidered too high for many design groupsand there fore the concep t of the remotedesign station was born.

4. CONVENT IONAL C.A.D. SYSTEMMost conventional C.A.D. systems have ahardw are c onfi gur atio n as (Fig 4) and cost$300K to $400K for a 2 termi nal system.They are usuall y ba sed ar ound a 16 bitcomputer wi th a full complement of memoryand a large disc. The termin als are fastresponse video displays, frequentlycolour, e quiped with tablet, functionkeyboard, etc. The syste m is suppo rted byhigh speed magne tic tape and a fastprecision plotter.The systems are essentia l tools in thedesign cycle of modern electronics,however, it is hard for local designoffices, with perha ps 2 or 3 desi gners tojustify the cost of a full system.Fortunate ly ULA's can be handled at thefront end with a much smalle r amo unt ofcomputer power.

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FIG. 4

f VDUDIT KEYBOARDSTATION TABLETFUNCTIONBUTTONS

CONTROLTTY JI

CPU

_i i

C O N V E N T I O N A LC.A.D. SYSTEM

~HIDH SPEEDPLOTTER I

VDUKEYBOARDTABLETFUNCTIONBUTTONSt DITSTATION5. TH E FERR ANTI U.L.A.

In unders tandin g the function of the remotedesign station it is necessary to realisethe Ferranti philoso phy behind their ULA (2)

5.1. INTERCON NECT LAYERThe ULA is cust omis ed by means of a singlelayer metall isatio n layer. This achievesfaster, more reliable, simpler processi ngthan multila yer technologies. This ismade possible by the gate structure usedwhich has a pseudo second layer formedby diffusing crossunders at every cell(Fig 5.) and by the pro ces s usedallow ing the Vcc and GND rails to passthrough the silicon thereby simplifyingthe interconnection problem./

FIG. 5 TYPICAL U.L.A MATRIX CELL

5.2. UTILISATIONMany of the Ferranti ULA's are designedas high volume producti on devices. Foreconomic reasons this implies an efficientuse of silicon area and theref ore the ULA'sare often rout ed to a very high densi ty,frequ ently in excess of 90% (Fig 6.)

5.3. FLEXABILITYA wide variety of functions includinglinear and digilin are often incorporatedin layouts implemented in Ferranti ULA's.It is the main aim of Ferr anti ULA's toproduce economical custom designs. AnyC.A.D. system must allow the engineer totake advantage of the potential ly highpacking densitie~ and flexibilityavailable.

5.4. THE ULA TOPO LOGYThe range of ULA types varies from i00 to2000 gates with a wide va riet y of speed/p o w e r / l i n e a r c a p a b i li t i e s .They all consi st of a matr ix of cellsencased in an anulus of peripheral cells(Fig 7. ).These peripheral compo nents fall intotwo categories, those which have standardmetall isation patterns, and those whichare on a grid allowing the engine er todesign his own periphera l circuits.The standard metallisatio ns are availablefor T.T.L. inputs, Tris tates, Powerdrivers etc, etc.The peripheral components on a grid givethe engineers the flexability to designtheir own peripher al circuits.

6. THE REMOTE DESIGN STATIONS6.1. Initial Desig n Conce pts

The initial design concept for the remotedesign station was a low cost syste m($40/50K) w hich wou ld put as much of themain C.A.D. design facility as possiblein the custo mers office. The syste mwould obviou sly require a cpu with discbackings store, drawing reading machineinput and some form of graphics edi tingfacility. In practice the system becomesvery similar to the conventional C.A.D.system above but the differenc es are inthe degree of power a vaila ble in the CPUsetup and the lack of large peri pher alsupport. It will have only one Desig nTerminal. On the final proposed systema multiuse r facility will be availablethrou gh a none design t ermina l port i.e.a teletype.The final remote design stationconf igur atio n is as Fig 8.

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FIG. 6 A U . L . A . M E T A L L I S A T I O N ~ A S K

x

GND

g

CELLS< I

FIG. 7 U . L . A . P E R I P H E R A L C E L LA R R A N G E M E N T S

ILARGEDIGITISER

I - . . . . . . . "1I II PLOTTER optional.I. . . . " 7 . . . . J

:I

CPU

I CONTROLTTY

TELEPHONE_~SERVICE

II GRAPHICS IDISPLAYandJOYSTICK

F I G . 8 R E M O T E D E S I G N S T A T I O NC O N F I G U R A T I O N

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Full facilities are available in the PDPII/23 for entering scaling, plotting andediting the ULA layout. Facilities alsoexist for writing of the test program andentry of the logic description. Accessis then availa ble to the main C.A.D. systemvia the Modems and DECNET to run this dataon logic simulation and design verificat ionprograms.

6.2. HARDWARE CONSIDER ATIONS6.2.1. Computer

It was decided to have the system arounda PDPII/23 for 3 main reasons:-

(a) It was the sma llest of thePDPII family thg~ wouldsupport the RSX'~)o peratin gsystem in a multius er situa-tion.

(b) It was reas onab le cost.(c) The learning cycle for ourengineers underst anding it

and its software would beminimum.The last conside ration is probably oneof the most i mport ant factors and afactor often over looked in new systemdesign.

6.2.2. DiscThe disc was an important c onside rationbecause initial estimates showed thatthe required data structure would notfit into a 32K word bl ock an d there foredata paging was going to be essential.Floopies were dismissed, partly due tospeed, but large ly due to conce rn thatthey may not perform reliably enough inthe field. Not all engineers ap preciatethe importance of floppy disc backup andreplacement.Consid eration was given to Winches terdiscs. The main problems here were thedifficul ty of system backup on a systemwithout magnetic tape and our lack ofsupport /knowle dge on a Winche ster basedRSXlIM systemThe system was eventually based aroundtwin 5MB hard discs (RL01's), one fixedand one removable.

6.2.3. Edit Term inalAlthough a colour display with equivale ntspeed of response of the major C.A .D.systems seemed desirable, a mono displaywas chos en on ground s of cost.

Colour, althoug h effective, was notconsidered the economical for singlelayer metal ULA's. It was felt that ifdesigners had their own terminals theywould live with a screen repaint timeof a few seconds.Initially the Tektronix 4010 display waschosen but later a compatible rasterscreen with joystick control was sub-stituted.

6.2.4. Digitisi n~ TabletThis was an area in whic h that therecould be no compromise on what wasoffer ed with a full C.A.D. system.Althoug h work ing in the area of automaticlayout and autom atic layout aids themanua l layout is still importan t. If aULA is being desi gned for high packingdensities then manual layout or manuallayout completio n will still need to beused. This will result in a large draw ingand therefo re a large digitis ing tabletwill still be the most effectiv e way ofhand ling the layout.

6.2.5. PlotterPlotters are expensive but plots ofdrawings are essential. Althoug h Ferrantiare now using automatic layout inter-connection checking of all their ULA'sa plot of the layout is always required .ULA layouts are usua lly d rawn at thetradi tiona l 200 or 250 x size whic h resul tsin plots of up to 52 inches square. Dueto resolut ion even crude metall isationplots at this size need to be drawn reaso n-ably accurat ely (better than I0 mil). Thisresults in a requ irem ent for a largeaccurate pl otter or a smaller plotter withthe added complicati on of windowi ng soft-ware etc.The plan for the remote design station isto make the plott er an option. If noplotter is available on the system fileswill be tran sfer red down the line to theDesign Centre for plotting. These canthen be despatched to the customer byone of the courier services.

6.3. System SoftwareThe remote de sign station is a tool forULA design and not a general purposegraphic system. Its operatio n is basedaround a number of specifi c tasks, allof whic h will be run in the RSXlIMoperating system. They will be controlle dby indirect comma nd files to make thecomputer operation invisible to the user.

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6.3.1. Layout Design EntryThis is the entry via the drawi ng readi ngmachine of the layout designers pencilinterconnect pattern.All opera tions relate d to the topolo gy ofthe ULA are controlled by a table ofgeometry c haracteristic s of the array.This table contains information on cellpitch, track dens ity etc. (Fig 9.)

NUMBER OF BLOCKS IN MATRIC

NUMBER OF X + Y CELLS PER BLOCK

X + Y TRACK P ITCH

STANDARD PERIPHERALS ALLOWED

PERIPHERA L CELL LOCATIONS

MATRIC CELL BLACKCLOT H PATTERN

PERIPHERAL BLACKCLOTH PATTERN

CALIBRATION POINTS

ET C

FIG. 9 TABLE OF TOPOLOGY INFORMATION

FOR REMOTE DESIGN STATIONThe system extra cts the ULA typ~ from thefirst part of the job number and fromthis determines which table character-istics to use.Calibration points and deadband zonesare also set up via the table.After calibr ation the only data enteredinto the system at this stage is trackcentre lines and special matrix celllinks etc.Because digitising is time consuming thesystem allows all other operations, suchas data editi ng to be perf orme dsimultaneou sly at the edit terminalwhile digitising.

6.3.2. Layout Editi ngThis is perf ormed at the graphi cs terminalin conjunction with a joystick control ofthe curser. All the usual commands toadd and modify data exists. Two inter-esting features are the wind ow andbackcloth facilities.As on all systems it is neces sary towind ow into the area required in order toobtain sufficient resolution for easyediting. As this system is desi gned toedit the ULA matri x and all cells areidenti fied by refer ence nu mbers (rows i-

columns A-Z) the opera tor can call up anygiven cell area by typing its refer encenumber. The area then disp laye d iscentralised on that reference cell. Scaleand therefore number of cells displayeddepend s on the versi on of the wind owcommand used with the cell referencenumbers.A 'backcloth' is avail able to help opera-tors determine locations of contact holesetc, on a given matrix. This is a symboli creprese ntation of the ULA diffusion andconta ct holes. It can be switched on athalf and full levels. Half level is forexperienced users and has less informationthan displ@y ed on the full backclot h.

6.3.3. Logic Diagram EntryThe key reference document or data base inthe Ferran ti C.A.D. system for ULA'soperating at their Microele ctronics DesignCentre is the logic diagram. At the centrethis is enter ed into the system thr oughthe Appli con system as a comple te gr aphic aldrawing.The same logic data is to be entered atthe remote design station but initiallythis will be typed in as a net wor k list,rather than entered as a diagr am to savethe complicati on of data structures witharcs and text etc.This logic diagram will then form thereference tables for layout and logicchecking routines.

6.3.4. Test Prog ram EntryAs on the main system the desi gner willenter the device test program.This is in the hig h level lang uage SAM (4)and is used for both logic verif ica tionand prod ucti on of the final A.T.E. ~rogram.

7. COMMUNICATIONSThe most imp ortan t feature of the remotedesign station is its communicati on linkwith the main Ferranti C.A.D. system attheir Mic~oel ectroni cs Design Centre.

This link will be at 2400 Baud on thenormal dial up telep hone networks. Thecommunicat ions will be controlled byDECNET (5).The engineer at the customer site willtransm it to the centre 3 main fil es:-

(a) layout(b) logic(c) test pro gra m

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In addition he will send message filesreq uest ing runs of the logic simulator,interconn ection check program etc. Theoutput of these runs, error messag es etc,will be sent back later the same day orthe following day by the same links.In this way the customer engin eer willhave full access to the speci alise d ULAsoftware necessar y for complete designverification.

REFERENCESI. Automat ion of Design for Uncommi tted

Logic Arrays. - F.R. Ramsay D.A. C.802. ULA Tech nica l Handb ook Issue 1 -

Ferranti Electronics Limited.3. RSXlIM Digital Equipment Corpor ation4. SAM Integrated Circuit TestingLanguage - Ferranti El ectronics

Limited. - Internal Doc ument.5. DECNET Digital Equipment Corporation.

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Cad System for Ula