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1983 , Volume , Issue Jan-1983

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1. In the controller mass flow is regulated by switching two valves The initial pressure Pigh is set by an inlet valve from a pressure source The final pressure Pyoy is achieved after opening an outlet valve which dumps mass Gas Supply Duty ji Port Actual Values and Status Information to GC 36 HEWLETT PACKARD JOURNAL JANUARY 1983 Fig 3 Block diagram of the elec tronic flow controller Copr 1949 1998 Hewlett Packard Co Fig 4 Basic elements of the capacitive pressure transducer intoa load A diagram of the system is shown in Fig 5 The time interval t during which mass transfer takes place is constant Therefore it is possible to determine the average mass flow rate Since we are dealing with almost ideal gases we assume that we have 22 400 milliliters per mole at standard temperature and pressure Thus we can calculate volumetric flow rate Average mass flow rate N1 N2 it so that Average volume flow rate 22 400 N1 N2 t or Flow rate Pxigh P iow 22 400V tRT milliliters per minute Control Sequence Flow rate is controlled by varying the amount of time that the sensor volume has to charge up to pressure Pitigh This is done by adjusting the valves on time duty cycle To control Fig 5 System for regulating mass flow pressure the same mechanism is used as for flow control with appropriate alterations in the control algorithm The timing sequence for a typical c
2. Diverging V x ing the reactor s etch performance for the doped polysilicon gate structure is shown in Fig To avoid generation of surface interface charge states late in the process it was decided to do the contact etch witha solution of aqueous HF An unexpected problem de UT 20 3 2060 07 004 058 tion printing m Photoresist as _ i A O0 118 y I 07 3 20 0 03 005 563 d b Photo aligner images produced by veloped The diode junctions produced before the contact etch step have such low leakage that a built in electric field is established in the circuit during the etch This field can have the effect of stopping the removal of silicon dioxide in certain contact holes namely n type contacts connected to p diffusions in p wells A detailed explanation of this effect is presented in reference 2 After this anomaly was elimi nated the contact hole etch process was defined using temperature control filtering and automatic handling This lithographic development work for CMOSC has re sulted in a typical ROM cell of 99 um area a static RAM cell occupying 2020 um and a random logic density of 350 gates mm Low Fabrication Cost Low cost today means maximum use of resources The development team began asa small group increased in size to handle tasks as they were encountered and is dissipating as the remaining problems are solved The production forc s
3. JANUARY 1883 KARD JOURNAL Copr 1949 1998 Hewlett Packard Co HEWLETT PACKARD JOURNAL Technica Information from the Laboratories of Hewlett Packard Company Contents JANUARY 1983 Volume 34 e Number 1 HP IL A Low Cost Digital Interface for Portable Applications by Roger D Quick and Steven L Harper This loop interface allows you to carry a computer system in your briefcase HP IL Interconnect System by James H Fleming Clever plugs and connectors and inexpensive two wire cords connect HP IL devices The Electronics Interface for the Hewlett Packard Interface Loop by Carl J Landsness Three level coding a custom IC and small pulse transformers are key elements A CMOS Integrated Circuit forthe HP IL Interface by Steven L Harper This IC available to OEM designers makes it easy to add HP IL capability to a product CMOSC Low Power Technology for Personal Computers by David E Hackleman Nor man L Johnson Craig S Lage John J Vietor and Robert L Tillman More functions and less power are the goals for this refinement of a standard CMOS process Advanced Oven Design Assures Repeatability in New Gas Chromatograph by Paul C Dryden Horace R Johnson Jr and Douglas H Smith Results are highly reproducible even without thermal conditioning before the first runs What Is Gas Chromatography by Fred W Rowland Here s some basic information for nonchemists Electronic Flow Control A New Level of Automation
4. A disc of 0 003 inch thickness produces fast turn off but does not hamper turn on A drawing of the inlet valve is shown in Fig 9 Fig 10 shows the completed electronic flow controller module Acknowledgments We would like to acknowledge Roger Nalepa for much of the original work on the flow sensor and Erika Rawlings for her design support JANUARY 1983 HEWLETT PACKARD JOURNAL 39 Copr 1949 1998 Hewlett Packard Co Kurt B Augenblick Kurt Augenblick was born in Philadel phia and attended Lehigh University receiving the BSME degree in 1971 and the MSME degree in 1973 He came to HP in 1977 with four years experience in the development of photographic products and a computer output mi crofilm system He contributed to the design of the 5880A GC and super vised the design of the electronic flow controller for the 5880A and is now Av ondale Division fabrication engineering manager Now a resident of Wil mington Delaware Kurt enjoys wood working soccer table tennis and fish ing He s married and has two children J Edwin Cusack Ed Cusack has been a production en gineer with HP s Avondale Pennsyl vania Division since 1970 He received his BSME degree from Villanova Uni versity in 1966 and his MBA degree from the Wharton Business School of the University of Pennsylvania in 1970 He s married and has two children Michael A Casale Mike Casale graduated from New Jer sey
5. clear IFC command is presumed to have been generated by this device and is stopped and error checked If the control ler active bit CA is set all other commands are stopped and checked since this device must have generated them When the talker active bit TA is set data frames are stopped and checked The listener active bit LA causes incoming data frames to be loaded into R2 R and passed to the device s microprocessor More than one of these bits can be set at once and the combined functions are performed as would be expected BUS7 BUS6 BUSS BUS4 BUS3 BUS2 BUSI Register 0 Status BUSO Read Write RFC sc CA TA La ssra Register 1 interrupt Reed c2in cin Co FcR SROR FRAV FANS ORAV write c20UT ciour coour interrupt Enable Bits Register 2 Data Read TET TETE write CII D20UT D10UT DOOUT Register 3 Parallel Poll Read Raia 2 4 PPST PPEN PPPOL P2 Pi Po Write Register 4 Loop Address Serehpad ous aopa anos ano aoo apoo Register 5 Scratchpad Read Write kines Scratchpad Bits write Register 6 Scratchpad Read S E Scratchpad Bits Fig 2 Register map for HP IL interface IC Copr 1949 1998 Hewlett Packard Co The four least significant bits of register 0 perform certain special functions The send service request bit SSRQ causes the service request bit SRQ to be set in any HP IL data or identify message frames that are transmitted through a de vice so
6. Institute of Technology then Newark College of Engineering with a M BSEE degree in 1973 and joined HP the same year He s contributed to the jesign of the 5730A GC the 5880A GC 4 and the electronic flow controllerfor the 5880A He s named as aco inventoron a patent application on the flow control ler Mike was born in New York butcon siders himself a native of Paramus New Jersey He now lives in Hockessin Del aware and enjoys music gardening tennis volleyball swimming and soc f cer Andrew J Murphy Andy Murphy holds BSME and MSME degrees from the University of Dela ware With HP since 1977 he s served as a process engineer mechanical en gineer on the 5880A electronic flow controller project and fabrications 2 quality control supervisor He s a member of the ASME Born in Balti more Maryland Andy is married has three children and lives in Wilmington Delaware He s a camp counselor and enjoys golf and reading HEWLETT PACKARD JOURNAL Bulk Rate U S Postage Paid Hewlett Packard Company OOOZ07O7TEEEBLACECAOO t C A BLACKBURN DHN HOPKINS UNIV PPLIED PHYSICS LAB OHNS HOPKINS RD AUREL MD 20707 CHANGE OF ADDRESS 5953 8507 SA Alow 60 days Copr 1949 1998 Hewlett Packard Co
7. With 85 000 transistors on a cm chip Fig 8 and a total operating power dissipa tion of 0 25 mW it is truly low power This integrated circuit contains a 61K ROM a 2 2K static RAM a 100 Fig 8 Photograph of a C ACKAF JRNAL 27 Copr 1949 1998 Hewlett Packard Co Given a standard CMOS device as depicted by the inverter cross section in Fig 1 one can draw a parasitic transistor pair schematic as shown in Fig 2 These parasitic devices are not necessary for the functionality of the logic but are a result of the structure obtained with standard CMOS processing This circuit has the current voltage relationship shown in Fig 3 With no injected current the parasitic transistors have a high resis tance However if enough current is injected into the n substrate and collected by the p well the two transistors will switch to the low resistance portion of the I V curve This stops functional oper ation of the circuit and in a calculator will discharge the batteries The circuit can sustain this low resistance latch up until the cur rent drops below 1 An important objective in CMOS process design is to make V1 and 1 unattainable either during normal circuit operation or as a result of external stimuli Reference 1 D B Esterich The Physics and Modeling of Latch Up in CMOS imegrated Circuits Technical Report No G 201 9 Integrated Circuits Laboratory Stanford Electronics Laboratories Stanford Universit
8. a flowing liquid stream a much gentler process than vaporization 8 M IE What Is Gas Chromatography by Fred W Rowland About Columns The heart of the gas chromatograph is the heated tube with a coating of some sort on the inner wall called a column In the early days of GC columns were made differently They were glass or metal tubes usually of or Ye inch inside diameter packed witha finely divided inert support material which carried the active coat ing This construction was necessary because the detectors then available were not very sensitive and fairly large by today s standards sample injections were needed The column had to contain sufficient material to avoid saturation by the sample com ponents A packed column met this need The problem with packed columns is that they do not do a very good job of separation This is largely because their inner diame ter permits diffusion perpendicular to the flow direction broaden ing the peaks and causing them to run together Today s capillary columns have inside diameters of about 0 2 mm with the active material coated on the inner wall This geometry effectively suppresses lateral diffusion yielding ex tremely narrow peaks and great separating power However such columns contain very little of the active material and cannot accommodate large sample sizes They are often used with an injection splitter which vaporizes the sample and then dum
9. a patent related to the HP IL protocol i 0 Born in Medford Oregon he is married bai has four children is expecting a fifth child and lives in Corvallis Oregon He is the coordinator for the local Boy Scout troop and is involved in church activities which have included a two year mission in Brazil His other interests are sports hunting folk guitar science fiction and dining out Roger D Quick Roger Quick joined HP in 1975 with ten years experience in CAD and MOS IC design His work at HP has included development of the electronics for the HP 10 and HP 19C Calculators and serving as project manager for the HP 41C software and electronics the 82143A Printer and the HP IL system and components Roger isa member of the Association for Computing Machin ery co inventor on a patent related to the HP IL and co author of two other articles related to his contributions at HP one appearing earlier in the HP 4 Journal Born in Berkeley California he attended the University of California at Berkeley earning a BA degree in mathematics in 1964 He is married lives in Corvallis Oregon and owns an assortment of chickens ducks cats two dogs and a goat His outside activities include being the campus manager of the site interaction committee at Oregon State University breeding yellow Labradors and collecting old Lotus sports cars JANUARY 1983 HEWLETT PACKARD JOURNAL 9 Copr 1949
10. bicycling and playing handball JANUARY 1883 HEWLETT PACKARD JOURNAL 29 Copr 1949 1998 Hewlett Packard Co Advanced Oven Assures Repeatability in New Gas Chromatograph An innovative oven design gives the chromatographer access to the full capabilities of the new fused silica capillary columns by Paul C Dryden Horace R Johnson Jr and Douglas H Smith you ll probably see at least one gas chromatograph This instrument separates complex mixtures of organic chemicals into their individual components allow ing them to be measured and identified one at a time In the last several years a strong trend has developed toward the use of capillary columns in these instruments These columns have inside diameters of about 200 300 micrometers and havea thin layer of active chemical coated on their inside walls They yield extremely narrow peaks permitting separation of components that would merge into a single peak in the older packed columns Two problems of capillary columns are fragility many are made of glass and chemical activity of the tubing These problems were solved in 1979 when Hewlett Packard introduced columns made with fused silica tubing The new HP Model 5790A Gas Chromatograph Fig 1 is designed to permit full use of the separating power inherent in the capillary column It achieves this through a novel oven design which provides a very uniform and precise thermal environment for the column a microprocess
11. cassette drive were used with an HP 85 the rate would be 350 bytes per second for long transfers and about 1100 bytes per second for short ones Two HP 85 Computers could communicate with each other ata little less than 1700 bytes per second across the HP IL Clearly the HP IL is fairly slow when compared with the HP 1B However the data rate and other features of this interface system are well suited to the primary area of intended application low cost battery powered portable systems Steve Harper This strategy should make the HP IL and devices using it widely available relatively soon Documentation One of the most important parts of the component sales effort is the supporting documentation There are three publications that contain the needed information For a first exposure to the HP IL a prospective user or designer can read The HP IL System An Introductory Guide to the Hewlett Packard Interface Loop With Hewlett Packard s help this book was written and published by Osborne McGraw Hill The HP IL Interface Specification provides continued on page 9 JANUARY 1983 HEWLETT PACKARD JOURNAL 7 Copr 1949 1998 Hewlett Packard Co In most projects connectors and interconnection systems do Not typically receive the level of concentrated design effort that the other electrical and mechanical sections do even though a study of service and reliability records shows interconnection problems rank among the maj
12. circuits which by themselves are not well balanced with analog differen tial amplifierscomparators Concentrating on the trans formers has proved more cost effective for the present The design results have been very rewarding With the design approach outlined here prototype systems that failed the susceptibility test at 100V transient amplitudes were able to handle 500V to 1000V transients and did not exhibit any transmission failures below a field strength of 5V meter Electrostatic Discharge With the proliferation of rather sensitive MOS circuits in today s electronic products susceptibility to electrostatic discharge ESD is a major reliability concern All HP IL products are required to exhibit no permanent failures and most will exhibit no temporary failure when a 300 pF capacitor charged to 15 kV is discharged through a 500 ohm resistor to any product surface This is a very high energy pulse compared to those typically generated by a user shuffling across a carpet Products interfacing to the HP IL will generally follow one of three general ESD protection approaches an earth grounded Faraday shield a floating Faraday shield and insulation of circuits This creates an interesting problem when a device with a floating Faraday shield is connected in the system The original interconnect design went to great efforts to insulate and otherwise protect the interface conductors so that a discharge could not occur to the wires an
13. connected in series with the capacitor forming an LC oscillator net work Pressure applied to the fixed volume moves the baseplate closer to the fixed plate increasing the capaci tance and reducing the operating frequency of the LC net work Thus a change in pressure is translated into a change in frequency which is measured and processed by the microprocessor There is actually a minute change in the transducer volume as the baseplate moves but its effect is negligible so the volume can be considered fixed Flow Sensor Theory The sensor is assumed to have a fixed volume and is Flow Pressure Setpoints Limits etc from GC Fig 2 Mode 5880A Gas Chromatograph is now avallable with an optional electronic flow controller capable of controlling either mass flow or pressure The controller is also available as an accessory for existing 5880As maintained at constant temperature According to the ideal gas law PV NRT where P is the pressure V is the sensor volume N is the number of moles contained in the volume R is a universal gas constant and T is absolute temperature If a volume has a known temperature and pressure at some time t1 and if we then allow some mass to escape from that volume such that at time t2 we have a lower pressure we can use the ideal gas law to calculate the amount of mass transferred Thus N1 Pyigh VIRT and N2 Prow VIRT so that N1 N2 Pigh PLow VIRT
14. for Gas Chromatography by Kurt B Augenblick Michael A Casale J Edwin Cusack and Andrew J Murphy Now the chromatographer can have precise control of either pressure or mass flow rate In this Issue E W Portable low cost battery powered plug together systems some small enough to fit in a a briefcase others larger and augmented with more conventional products such as personal Es computers and plotters we can expect to see more and more of these systems because EZ thanks to anewinterface system called the Hewlett Packard Interface Loop or HP IL they re going to be much easier to put together When instruments computers and peripheral devices are designed according to the specifications of the HP IL they can exchange data commands and other messages using only two wires The HP IL is called a loop because that s the way the wires are connected out of one device and into the second then out of the second and into the third and so on back to the first device The design of the HP IL is based on the Hewlett Packard Interface Bus or HP IB an industrywide standard interface for higher performance systems also known as Standard 488 of the Institute of Electrical and Electronics Engineers Because the HP IB makes automated measurement and control so much more avail able its impact on the ways such things are done has been tremendous The HP IL s impact is likely to be of Similar magnitude What the devices on the HP IL do is simila
15. information as a function of time using two signal levels The HP IL uses a three level code in which logical infor mation is encoded as a function of signal level transitions Four distinct logical bits 1 0 1S and OS are defined as shown in Fig 2 1S and OS are specially encoded versions of 1 and 0 respectively and are used only within the thr control bit segment at the start of each eleven bit message frame Fig 3 The first control bit also serves as a sync bit for the frame This provides an unequivocal start of frame reference if the loop gets lost for any reason e g power failure or external interference The particular code de fined here is optimized not for density but for reliability While a single level transition per bit is possible i e 1 positive transition O negative transition that ap proach would be more sensitive to glitches than the HP IL code where a sequence of two transitions is necessary be fore decoding a bit Another advantage to this particular code is the absence of any de level This is an advantage for transceiver pulse transformers which don t operate very Fig 1 Opened HP 82160A HP IL Interface Module showing internal electronic components JANUARY 1 EWLETT PACKARD JOURNAL 11 Copr 1949 1998 Hewlett Packard Co at ie til efficiently with dc bias more on this later A very important feature of the three level code is that the bits within a message frame are comp
16. is a microprocessor based system with a Z80 CPU as the main processing element Fig 8 is a block diagram of the system The sensor oscillator output signal is fed to the waveshape and multiplex circuits which are designed to receive the analog signal and convert it to TTL logic levels The counter chain counts the number of signal periods that occur in a fixed amount of time Hence the digital word that is given to the Z80 is proportional to the signal frequency The processor calculates the corre sponding pressure for that channel decides what corrective action needs to be taken and outputs a digital duty cycle word to the duty cycle generator The outputs to the valve driver circuit are pulses with an on time proportional to the magnitude of the digital duty cycle word The maximum on time is 50 milliseconds and resolution is better than 1 microsecond Data transfers are controlled by the 5880A interface sec tion During each 5 Hz period the Z80 is forced into a dormant state and control of local memory is given to the 5880A The GC and the Z80 communicate by direct mem ory access DMA the GC is permitted to read and write in the local data area of the Z80 SSK Fig 9 Inlet valve is designed for fast switching speed Electronic flow controlier module Fig 10 Inlet Valve The ideal control valve would have an infinite speed of response This would give an exact linear relationship be tween the drive duty cycle an
17. link To do this pach HP IL message is contained in an eleven bit frame The first three bits C2 C1 and CO carry the control information and the following eight bits D7 through DO specify the particular message or data Because much of the same information flows on the HP IL as on the HP IB the device address range is the same However since the HP IL does not have the electrical load ing limitations of the HP IB the loop can handle up to 31 devices at one time using simple addresses If devices capa ble of accepting double addresses are used as many as 961 devices can be on the loop at the same time The bits are encoded using a three level code sometimes known as the pulse bipolar code see Fig 2 and Fig 3 on page 12 A logical one consists of a positive pulse followed by a negative pulse and a short idle period A logical zero simply uses the reverse order of the pulses This code trades off some density for simple timing requirements good noise immunity and no dc component necessary for trans former coupling The first bit C2 af each frame is coded with double pulses This is useful since slightly different clock rates in devices around the loop require that even the bits within a message frame be asynchronous with respect to each other The start of frame reference provided by the first bit helps keep the bit count in synchronization in all system devices The three control bits indicate one of four major classes of
18. messages see Table I and provide end of record and service request information If the first bit is a zero a data message is indicated This permits the earliest possible decoding so that idle devices on the loop can immediately begin to retransmit a data frame to the next device on the loop thus maximizing loop speed for data The other three message classes are command messages ready messages and identify messages The purposes of data and command messages are obvious and identical to those for the HP IB Ready messages are a special class for handling certain handshake tasks on the serial loop Iden tify messages are the means for performing the parallel poll function on the HP IL Generally there is only one message frame on the loop ata time The handshake sequence for most messages is quite simple The originating device whether it be a controller or talker is required to wait until the current frame returns to its source before initiating the next message The desig nated receiving device simply stores the current frame until the device is ready for the next frame Then the receiving device sends the current frame back to its originator In this manner slow and fast devices can coexist quite nicely on the HP IL This handshake sequence works well when there are only one or two receiving devices since the idle devices on the loop pass on the message frame very rapidly However in situations where all of the devices on the loop
19. nor timing is very critical in detecting the three level code This makes it ideally suited for the HP IL because the detector circuits can be very simple and inexpensive Moreover reliability may actually be improved by intentionally increasing the transi tion times at the detector using a low pass filter toenhance noise immunity All of these advantages of the three level code are coun tered by only one major drawback generating and detect ing a three level signal in a basically digital two level system As we will see later the answer lay in the use of simple pulse transformers Transceivers The HP IL is a two wire balanced differential interface with both transmitter and receiver electrically isolated from the interface cable The isolated operation there is no ground on the wires eliminates many system noise prob lems such as electromagnetic interference EMI suscepti bility and radiation This is especially important because Fig 3 The HP IL uses an eleven bit message frame consist ing of three contro bits and eight data bits The first control bit also serves as a sync bit TW TS 2xTW a Desired Output Actual b ov mW Tw gt lt Ts Le 3 output Fig 4 Rise time distortion two level code a Input pulse waveform b Desired dashed line and actual output pulse waveform of circuit shown in c given input shown in a c Circuit block d
20. of field oxide Fig 1d im proved control of the out diffusion of the implanted source drain junctions and increased integrity of the gate oxide edge Leakage current can be decreased by inhibiting the thinning of the field oxide bird s beak during the contact etch dimension b in Fig 3a Thinning this oxide region below 50 nm can result in a nondestructive break down that increases leakage currents Fig 3b is an SEM scanning electron microscope photograph of an actual contact hole cross section High Device Density The circuit density objective was to allow a typical cal culator product to be designed with a minimum of IC chips 24 HEWLETT PACKARD JOURNAL JANUARY 1983 boron implant h Phosphorus is implanted for n sourceldrain re gions mask i After contact etch mask 6 j Metal deposition and patterning mask 7 After this step a passivating layer of silicon nitride is deposited over the circult and bonding pad openings are etched using mask 8 not shown Metal Specifically we wanted a minimum three fold increase in the functionality of a typical integrated circuit designed in the existing CMOS process To achieve this increase indi vidual device dimensions were reduced so that three times as many devices can be fabricated in the same chip area 1 1 projection scanning lithography is used to define the small patterns required With this technique a photomask con sisting of an exact sca
21. of one and one half years in his own engineering consulting business Jim has D worked for HP since 1963 at five dit a ferent divisions on a variety of prod ucts the latest being the HP 41C and HP IL peripherals interconnec tion Born in Oakland California Jim served in the U S Navy and before joining HP did mechanical design for a toy making firm He and his wife are both licensed pilots and enjoy packing their son and daughter in an old Cessna 172 for sightseeing trips around the Northwest or for visiting relatives in the San Francisco Bay area Jim s classic automobile hobbies are going on the shelf for several years to allow time to design and build the family dream home in Albany Oregon 8 HEWLETT PACKARD JOURNAL JANUARY 1983 Copr 1949 1998 Hewlett Packard Co a b e Fig 4 HP IL conn pulse transformer set b and interface IC c r a the designer with the HP IL definition This document con tains all the necessary information to determine that a de vice is truly compatible Format and content are very simi lar to IEEE Standard 488 The description specification and use of the HP IL CMOS IC are given in The HP IL Integrated Circuit User s Manual This last document pro vides fairly detailed electrical and firmware design exam ples as an implementation guide All three documents are included in the HP IL Interface Kit In the near future the major e
22. say of a flexible disc drive The interface functions handle the communication of messages between the device and the rest of the interface system Consequently the inter face functions in each device must be the same to maintain compatibility and the designer must implement these func tions in strict accordance with the interface s protocol specification Like the HP IB the HP IL is a master slave system One device is designated as the system controller and is respon sible for bringing up the system when the power is turned on This controller sends commands to configure and con trol the loop and initiate transmission of data from one device to another The controller interface function is active in only one device at a time on the loop Protocol is pro vided to allow passing of the controller responsibility to another device so that multiple controller devices can take turns being in charge of the interface system The talker interface function permits a device to supply data when instructed to do so by the active controller There can be only one active talker on the loop at a time The listener function allows devices to receive the talker s data but only at the controller s command There can be multiple listeners at one time on the loop Often a device will have both talker and listener capabilities Controllers almost al ways have the talker and listener functions Ina typical loop operation the controller might begin by send
23. special JANUARY 1983 HEWLETT PACKARD JOURNAL 3 Copr 1949 1998 Hewlett Packard Co Address 1 Address 2 Printer Cassette Talker Listener Listener Calculator Talker Listener Controller Address 0 Plotter Voltmeter Talker Listener Address 3 Listener Address 4 Fig 2 Typical Hewlett Packard Interface Loop system Mes sages are circulated around a loop Only controllers and talk ers can originate a message but all devices can retransmit a received message Each device receives the message acts upon itif required and retransmits it to the next device until the message returns toits originator Thus each HP IL device only has to drive one other device regardless of the number of devices on the loop cable to permit device to device spacing up to 100 meters The loop structure has one disadvantage Because the data must pass through each device and return to its source all devices in the system must be powered up and fully functional If one device fails it is likely that the entire system will not work Interface Electronics Once the basic architecture was chosen work proceeded to design a low cost low power electronic interface to the system The combination of a custom CMOS complemen tary metal oxide semiconductor integrated circuit and miniature pulse transformers is the result The electronic interface links each device to the next thro
24. the controller the power down function can permit unattended remote operation of an HP IL system for extended periods Another of the added functions is the autoaddress func tion The HP IB requires the user to set device addresses manually by means of switches on each HP IB device It is the HP IB user s responsibility to ensure that no two devices have the same address The loop structure of the HP IL on the other hand allows the controller to assign sequential addresses automatically to the devices on the loop The controller can find a particular device on the loop with the device ID function The controller sends the talk address command followed by a special message that causes the device to send a string of characters containing for example the device s model number The accessory ID function is similar but it allows the device to return a single byte code indicating the type of device and its capabilities Combined with the autoaddress function the accessory ID function allows the implementation of HP IL systems 6 HEWLETT PACKARD JOURNAL JANUARY 1983 that relieve the user and the user s programs of the problems associated with fixed device addresses and fixed device assignments For example an HP IL device can inform the controller that it is an ASCH printer or a 16 sector flexible disc Thus an HP IL user can command the controller to Print a File and the controller software will find an ap propriate device and p
25. the controller can be aware that the device needs attention Bit two is the only split bit in register 0 The read only bit indicates that a ready for command RFC frame has been received The write only bit set local ready SLRDY indicates to the interface IC that the device has finished executing the previous command and can pass on the ensuing RFC If it has already been received the RFC encoder automatically regenerates the RFC frame when SLRDY is set SLRDY automatically resets itself in 2us The clear interface clear received bit CLIFCR provides the only means of resetting the interface clear interrupt bit IFCR in register 1 CLIFCR also automatically resets in 24s Master clear MCL resets the integrated circuit to its power on state except for shutting off the oscillator Register 1 the interrupt register is totally split Since the incoming HP IL message frame has eleven bits more than one eight bit register is needed to contain it The three control bits of the received frame are loaded into the three most significant bits of R1 R Likewise the control bits of the frame to be transmitted to the next device on the HP IL must be written to R1 W before sending the frame out Often the incoming frame is simply sent on without change after it is read To save steps the control bits of the received frame in R1 R are automatically copied to R1 W whenever a frame is read by the device s microprocessor The other five bits in R1R represen
26. witha square cross section extends from the front of the cylindri cal shroud almost to the oven door The shrouds serve two purposes They create a barrier between the controlled air coming from the heater and the return air which has been cooled by the oven walls and Copr 1949 1998 Hewlett Packard Co Fan Guard LMM j Fig 2 Conventional GC oven design Columns mount for ward ofthe fan guard Conditioned air and return air mix in the column area door They also keep the controlled air in contact with the columns which mount either between the fan guard and the cylindrical shroud fused silica capillaries or just in front of the guard This combination of a flat fan and air directing shrouds is quite effective Chromatographers have taken for granted the need to run the oven through its temperature cycle at least once before beginning serious work This thermal conditioning was essential if the first few runs were to resemble those made after the oven had equilibrated With the 5790A this thermal conditioning is not necessary The space where the column mounts is quite unaware of its own thermal history Table I shows data from five analyses made over a two hour period The oven and column had rested overnight at 120 C During each run the oven temperature rose from 120 C to 270 C at 10 C per minute The first run which was Cylindrical Shroud Sous Fan Shroud Door Guard Seal CL C2 Fig 3 5790A ov
27. 00 meters in length which may be terminated in any impedance equal to or greater than 100 ohms Therefore the transmitter specification is given as a Th venin circuit to make it independent of load with a nominal 100 ohm source impedance to absorb any trans mission line reflections and a voltage waveform as shown in Fig 6 Great effort was made to make the voltage and timing limits as loose as possible to allow for inexpensive electronics Shown in Fig 7 is a schematic of one implementation of the HP IL The design combines some very simple digital circuits with small pulse transformers Throughout the project design cycle the typical reaction to the use of trans formers was something less than favorable Transformers simply don t have the glamour of the state of the art Minimum Maximum 30 ns 950 ns 19 ps 120 ns 200 ns 1500 ns 10 us 1ps witha 20 meter HP IL cable Fig 6 HP IL transmitter wave form specification open circuit While only a logical one bit is shown all logical bits must con form to the same basic specifica tions with polarity changes made where appropriate JANUARY 1983 HEWLETT PACKARD JOURNAL 13 Copr 1949 1998 Hewlett Packard Co Vr 3834 Transmitter Control Logic 330 pF sa m m CMOS LSI Circuit technologies like LSI large scale integration and fiber op tics But the transformers have many redeeming qualities that made t
28. 1983 HEWLETT PACKARD JOURNAL 17 Copr 1949 1998 Hewlett Packard Co loaded internally only part of the data might be correctly read causing an error which would be nonrepeatable and very difficult to trace The extra logic eliminates this possi bility The on board oscillator provides the basic timing source for the entire interface IC This 2 MHz signal is used to sample the incoming HP IL data directly Since the nominal pulse width on the loop is 1 us each pulse can be sampled at least three times for increased noise immunity The clock is also divided down to form a 500 kHz two phase signal for use in the rest of the integrated circuit By writing the proper control register and bit the oscillator can be turned off or on When it is off the circuit draws less than 1 pA something very important for small battery powered de vices The incoming HP IL lines enter the detector and receiver control block where the pulse sequences are decoded Noise spikes are ignored The presence of a sync bit in the middle of the eleven bit message frame sets an error bit see pages 5 and 12 for sync bit and frame definitions Detection of a sync bit also resets the input pointer so that it and the ensuing bits of the frame are correctly loaded through the demultiplexer into the input buffer The input buffer the input register and R2 R form a three level first in first out FIFO buffer that is really only necessary in those rare instances w
29. 1998 Hewlett Packard Co How Fast Is the HP IL Determining the data rate for an interface is often difficult and misleading since it is usually dependent on highly variable hardware and software delays in the devices connected to the interface rather than the maximum specifications of the interface itself For any statement of data rate to be at all useful the condi tions under which the measurement is made must be carefully and completely specified The first important question is How fast could the HP IL be it the devices did not limit the speed Assume a loop with only two devices a controlier talker and a listener The talker is continu ously sending data frames to the listener Because the first frame bit determines whether or not a frame is a data frame as opposed to a command or ready frame the listener will immediately re transmit the frame after only a one bit delay and simultaneously load the frame into its buffer Similarly the talker can begin trans mitting its next data frame after receiving only the first bit of the previous data frame Error checking of the received frame is elther not done or is done in parallel with transmission of the following frame Under these conditions a continuous stream of data would fill the loop limited only by the HP IL timing specifications These specifications say that a frame can be sent every 49 us The maximum data rate that could possibly be achieved is then slightly
30. 1998 Hewlett Packard Co beginning Joe Marriott and Dave Palermo for setting the initial architectural and functional foundations which al lowed the HP IL to carry the HP IB experience into a totally new environment Tom Heger and Dave Sweetser for estab lishing the HP IL protocol and integrated circuit specifica tions and for the effective education they provided Bernie Musch for supporting the HP IL in the handheld computer area Gary Stadele and Carl Landsness for doing the first implementations and finishing the job and Dave Ricci for his guidance all along the way 104 plugs the HP the HP 41C arger Serie Further Reading about the HP IL S Harper C Landsness and R Quick Instruments to Small Computers Interface System Weds Electronic Design December 24 1981 pp 78 8 2 R Katz The Hewlett Packard Interface Loop HPIL Byte April 1982 pp 76 92 3 P S s Guide to the GPIB HPIL Digital Design June 1982 pp 48 52 Copr 1949 1998 Hewlett Packard Co The Electronics Interface for the Hewlett Packard Interface Loop This low low power serial int cables a three level code a CMO transformers by Carl J Landsness the driving objective was that it be compatible with small battery operated devices such as an HP 41C Programmable Calculator This dictated cost size and power requirements far below those of any other interfaces pres ently offered i
31. 1998 Hewlett Packard Co Electronic Flow Control A New Level of Automation for Gas Chromatography An innovative gas flow controller for the HP 5880A Gas Chromatograph offers a choice of pressure or mass flow control without instrument modification and independent of the gas measured by Kurt B Augenblick Michael A Casale J Edwin Cusack and Andrew J Murphy HE ACCURACY AND REPEATABILITY of gas chro matographic information are directly related to the performance of the chromatograph s gas control system Historically gas regulation has been handled in GCs by mechanical flow controllers which provide a con stant mass flow over a wide range of back pressures Fig 1 is a schematic representation of a gas chromatographic system Although mass flow control of carrier gas ismore popular at the present time the potential for improved long term reproducibility makes pressure control a valuable alterna tive For this reason a new principle of operation has been developed which permits the selection of pressure or mass flow control without instrument modification The ar chitecture of the system and the speed of response of the controller make it possible to program both flow and pres sure to vary linearly with time providing another degree of freedom to the chromatographer This new performance is available in an electronic gas flow controller for the HP 5880A Gas Chromatograph Fig 2 The new flow controller is compatible wit
32. ITT V 24 Both use many parallel conductors and so their connectors are large requiring 24 and 25 pins respectively Both of 1976 SEVERAL DIVISIONS of Hewlett Packard be Talker Listener Listener Talker a n Bus Lines b Fig 1 a Star network architecture The controller located at the center must have an O port for each of the other devices on this interface system b Parallel bus network architecture Each device on the bus must be able to drive the combined load presented by the other devices on the bus these interfaces use bipolar device technology which be cause of inherently high current drain consumes consider able power The large connector size and power require ments are obviously not compatible with small battery operated devices such as the HP 41C Programmable Cal culator Because size cost and power consumption are critical requirements for portable low power systems a different interface design is required Since many applications do not require the high speed performance of the HP IB a slower simple bit serial two wire link between devices was chosen This choice and the design of a new miniature connector system provided the solution to the size problem and helped alleviate the power consumption and cost dif ficulties System Architecture In any interface system it is very important to be able to connect more than just two devices to
33. LACS Listener Active State PONS Power on State e ITS Receiver Immediate Transfer State Fig 7 a State diagram of parallel poll function Mnemonic definitions for b messages and c interface states firmware When a disable command PPD or an unconfigure command PPU is received it must be decoded by the pro gram and the proper bit cleared in the parallel poll register of the interface IC Acknowledgments The original architecture of the HP IL interface IC and the sometimes tough job of making sure that the logic was capable of duplicating the external behavior of the state diagrams were done by Dave Sweetser and Tom Heger Carl Landsness did the analog circuit design Most of the digital logic and circuit design was done by Mike Pan Project management was ably handled by Roger Quick Copr 1949 1998 Hewlett Packard Co CMOSC Low Power Technology for Personal Computers To meet the growing need for integrated circuits with more functions and lower power consumption an improved CMOS process has been developed at HP s Corvallis Division by David E Hackleman Norman L Johnson Craig S Lage John J Vietor and Robert L Tillman tary metal oxide semiconductor process has been developed at Hewlett Packard s facility in Corvallis Oregon Required by the increasing integrated circuit com plexity of personal computers CMOSC meets several objec tives that affect all phases of IC design and development The o
34. The 5790A provides two user accessible calibration parameters which can be changed from the front panel The chromatog rapher can calibrate for maximum accuracy at any tempera ture by altering the absolute temperature parameter or can continued on page 33 Table Retention Time Stability Time Retention Time minutes Injected Peak 1 Peak 2 0745 3 977 12 814 0808 3 978 12 813 0832 3 978 12 813 0931 3 978 12 814 0958 3 977 12 814 Injection Manual split ratio 150 1 Temperature program 120 to 270 C at 10 C min Retention time measurements Hewlett Packard Model 3390A Integrator JANUARY 1983 HEWLETT PACKARD JOURNAL 31 Copr 1949 1998 Hewlett Packard Co Consider a stream of gas flowing through a heated tube If we inject a small sample of a liquid at the upstream end and if the temperature of the tube and gas are above the boiling point of the liquid the sample vaporizes and is swept down the tube It emerges at the far end unchanged except for the broadening effects of diffusion This is true even if the liquid injected is a mixture of several compounds Now suppose that the inside wall of the tube is coated with a thin layer of some nonvolatile chemical The sample molecules are torn between the desire to remain vaporized because of the temperature and the desire to leave the gas phase and enter the coating because of various kinds of chemical affinity The result is that the original sample vapor is s
35. a frame be asynchronous with each other The transmit encoder receives data to be sent on the HP IL from several sources The input register multiplexer passes frames that must be immediately retransmitted with as little delay as possible The output register multiplexer provides the frames that originate locally at the device Other inputs to the transmit encoder provide modification of frames on the fly for service request and parallel poll responses and for regenerating a received handshake frame when the de 18 HEWLETT PACKARD JOURNAL JANUARY 1983 vice has finished executing the previous command frame Certain HP IL commands contain a device address A device s address comparator checks to see if the address in the received command is the same as the address assigned to the device The acceptor and driver programmed logic arrays PLA provide the real intelligence of the interface IC The frame type and state of the device controller talker or listener are the primary inputs to the PLA Its outputs control virtu ally the entire integrated circuit except for the interface circuitry to the device s microprocessor Register Map Fig 2 is the programmer s model of the HP IL interface IC which shows the detailed functions of the various registers Register 0 is the status register Its bits encode the control ler talker or listener state of the integrated circuit When the system controller bit SC is set an incoming interface
36. able of calling and executing another one a process called chain ing Thus very complex profiles can be generated and exe cuted automatically Convenience Features The 5790A contains a stopwatch function which reads in both minutes and reciprocal minutes This simplifies mea JANUARY 1983 HEWLETT PACKARD JOURNAL 33 Copr 1949 1998 Hewlett Packard Co surement of gas flows which typically are measured by timing the passage of a soap film between two volume marks The keyboard can be locked to prevent accidental damage to an analysis While the keyboard is locked any setpoint can be displayed but none can be altered Troubleshooting Aids The 5790A is controlled by a 6803 microprocessor lo cated in the chromatograph controller module just to the left of the oven door The processor controls the instrument functions triacs sensor multiplexer oven cooling etc through a group of 14 control bits which are echoed back to the processor for checking Whenever the processor is not engaged in some control task it runs a series of internal diagnostic tests Seventeen error conditions are recognized each of which produces an error indication in the front panel display If any serious error persists for more than one minute all heaters are shut down to prevent possible damage to the instrument Once an error has occurred there are several ways to track it down The contents of selected memory locations can be displayed on t
37. ame Retransmit Fig 3 Simplified flowchart of the response of an idle device on the HP IL JANUARY 1983 HEWLETT PACKARD JOURNAL 19 Copr 1949 1998 Hewlett Packard Co Table HP IL IC Interrupt Flag Response Chip Status Interrupt Flags Received F1 Notes rame sc CA TA LA FRAV FANS ORAV DOE X x 0 0 Automatic retransmission X 0 0 1 S CPU retransmission X x 1 0 E S Source automatic error check x 1 0 1 S S CPU retransmission IFC 0 0 x x Automatic retransmission 0 1 x X S CPU retransmission 1 1 X x E E Source automatic error check and automatic source RFC if okay UCG e IFC SAG x o X x s Automatic retransmission TAG LAG match ACG TAG LAG X 0 0 0 Automatic retransmission amp SLRDY match X o X X Automatic retransmission e IFC x 1 x X E E Source automatic error check and automatic source RFC if okay Automatic retransmission after SLRDY S Source decoded Automatic retransmission S CPU retransmission or source no automatic error check S CPU retransmission E S Source automatic error check Automatic retransmission E S Source automatic error check CA TA LA 1 The bit is set high only if automatic error checking detects an error This combination has no effect on this bit mane AUX7 These are general purpose bits and may be used to sense
38. as three children coaches youth soocer ice hockey and track and field and is active in local youth sports pro grams as a board member and organizer Horace R Johnson Jr M Horace Johnson has been with HP s Avondale Pennsylvania Division since 1977 and has contributed to several projects related to gas chromatographs and accessories the latest being the 5790A GC A native of Philadelphia he received his BS degree In electrical en gineering from Pennsylvania State Uni versity in 1977 and is working for his MSEE at the University of Delaware He s a member of the industry advisory group of North Carolina A amp T State Uni versity and the Forum to Advance Minorities in Engineering He s a resi dent of Newark Delaware and his hobbies are microcomputing photography karate and guitar Paul C Dryden Paul Dryden was born in Council Bluffs lowa graduated with a BS degree in chemistry from Drexel University in 1968 and received his PhD degree in analytical chemistry from the University of Illinois in 1975 He joined HP s Avon dale Pennsylvania Division in 1975 and contributed to the design of the 8450A Spectrophotometer and the 5880A GC before becoming project leader for the 5790A GC Paul has two children and lives in West Chester Pennsylvania He s a photographer he s designed and built his home computer and he videotapes plays for a local theater group Copr 1949
39. ational Youth Science Camp He also participates in the local amateur radio emergency service and is interested in astronomy and square dancing David is married and building a home on 40 acres near Suver Oregon Robert L Tillman A section manager for MOS R amp D Bob Tillman has also worked on GaAs FETS and silicon process technology since coming to HP in 1971 Before that he worked on microwave IC design He is the author or co author of more than a dozen papers on silicon and gallium arsenide devices and technology Bob received a BSEE degree from the Mas sachusetts Institute of Technology in 1969 and an MSEE degree from Stan ford University in 1972 He is a member Ny of the IEEE and Sigma Xi Born in El as Paso Texas he is married has two 3 children and lives in Corvallis Oregon Bob s interests include reading mysteries playing slow pitch softball and gardening when he is not busy working on his wine cellar and seeking the ultimate investment scheme Craig S Lage Craig Lage is a graduate of the Univer sity of Wisconsin at Madison having received an MSEE degree In 1979 and an MS degree in nuclear engineering in 1978 He also has a BS degree in physics awarded by the California Insti tute of Technology in 1976 Craig joined HP in 1979 worked on CMOSC and now is a process enhancement project manager Born in Hinsdale Illinois he is married and lives in Corvallis Oregon His outside activities are
40. aveform of a two level code with a pulse width TW and pulse spacing TS TS 2TW in this exam ple In a delta distance code an error condition would occur if the comparator s output were distorted to the point where TW TS unable to distinguish pulse width from pulse space This would occur if TW TR 2 4 V7y Vy What does this mean If Vr is much different from half the signal amplitude or if the rise time is a significant percent age of pulse width detection becomes difficult if not im possible In other words the detector electronics would have to contain very accurate high resolution timing cir cuits In the HP IL we are dealing with pulse widths of about 1 us The circuits required to handle these fast pulses with good timing accuracy and resolution are generally beyond the cost power and size objectives of the HP IL Using a three level code it is generally only necessary to detect signal levels Timing is not critical However the particular code used in the HP IL does require some timing of pulse widths to distinguish the idle time TS following a bit from the positive to negative transition time 12 HEWLETT PACKARD JOURNAL JANUARY 1983 Fig 2 HP IL definitions for logical bits 1 0 15 and 0S TR within a bit From Fig 5 it is obvious that even if Vy is equal to Vy and transition time TR is equal to pulse width TW the worst case no error condition can exist What this says is that neither threshold level
41. bjectives include Low power consumption High device density Low circuit cost High reliability Improved latch up and electrostatic discharge ESD pro tection Standardized process models with design rule checks To accomplish these goals the project team had to de velop a new bulk CMOS technology and new concepts in IC facility design Adding spice to the challenge was a re quirement to merge the CMOSC technology into an existing IC clean room facility without disturbing production of the parent bulk CMOS process A N IMPROVED HIGH VOLUME CMOS complemen CMOSC Process Cross sections of a basic CMOSC structure at various points during processing are shown in Fig 1 First a thin oxide layer is grown on the silicon wafer surface and a layer of silicon nitride is deposited upon it Photoresist is applied and patterned using mask 1 to define the active regions This pattern is plasma etched into the nitride layer Fig 14 Mask 2 is then applied to define the p well regions Fig 1b A high energy ion implantation of boron is done to set the threshold voltages of the n channel transistors The p wells are diffused to the desired depth by along high temperature cycle ina dilute mixture of oxygen in nitrogen During this operation a 100 nm thick layer of silicon dioxide is grown in the field regions and subsequently is chemically etched away Photoresist is reapplied to the wafer and patterned using mask 2 again to mask t
42. concluded that rejection of 500V transients would provide reliable operation and that error checking and recovery techniques in the system software could handle the very rare occurrence of transients of higher amplitude The design of a receiver circuit to handle these transients turned out to be a major undertaking Testing verified that most of the interference is coupled to the HP IL cable as common mode Therefore the obvious solution was to de sign the receiver electronics with good common mode re jection over broadband frequencies However because of parasitic capacitance between the transformer primary and secondary this is not an easy task at higher frequencies 2 to 50 MHz in our case Two design solutions have been used in HP IL products to date One is an electrostatic shield between transformer primary and secondary the shield shunts common mode currents to device low rather than allowing them to flow to the load The second approach Fig 7 uses two very carefully balanced transformers in the receiver that operate on a principle very similar toa single shielded transformer except that the parasitic capacitance from each signal lead to device low must be well balanced Because of the difficulties in manufacturing very small transformers with shields it was found that the two transformer approach is more cost effective There are many other approaches to improved balancing but most require replacing the simple digital detector
43. d as a black box with access only through its HP IL connector If the device reacts in exactly the same way that a black box with the defining state dia grams inside would react then the details of the internal design are not important The device is functionally elec trically and mechanically compatible To implement the HP IL in a device the designer must first understand the state diagrams Equally important is a thorough knowledge of what parts of the state diagrams are implemented automatically by the interface IC and what parts must be handled by the device s microprocessor firmware The remote local interface function for example must be carried out totally by the program code in the microprocessor The receiver interface function on the other hand is largely automatic A specific example may help clarify the situation Fig 7 shows the parallel poll interface function The state dia gram indicates that when power is applied the parallel poll function must enter its idle state In the device micro processor s initialization routine for the interface IC the firmware should make sure that bit four in register 3 paral lel poll enable PPEN is cleared The interface IC leaves this bit undefined at power on and consequently after the IC s oscillator is turned on it might start responding to parallel polls when it should not unless the firmware prevents this The transition from the idle state PPIS to the standby state PPSS i
44. d couple directly into the product electronics After we tested many prototype products with great success the first system test found that a discharge to a product with a floating Faraday shield caused failures in an adjacent prod JANUARY 1983 HEWLETT PACKARD JOURNAL 15 Copr 1949 1998 Hewlett Packard Co uct The discharge to the shielded device raised the poten tial of all internal electronics to 15 kV which broke down the HP IL transformers in that device thus putting 15 kV on the cable conductors This broke down the HP IL trans formers in an adjacent device Asa result itis now required that HP IL devices withstand discharges made directly to the interface conductors even if they are not externally accessible The design approaches used to date to solve this problem have been very device dependent but have gen erally employed a combination of clamping filtering good grounding and transformer primary to secondary shielding Acknowledgments Special thanks goes to Ron Swerlein of Loveland Instru ment Division for much assistance in defining the electrical specifications Reference 1 Transient Voltages Suppression Manual General Electric 1978 pp 1 8 Cari J Landsness Carl Landsness was born in Madison Wisconsin He received the BSEE de gree from the University of Wisconsin in 1973 and the MSEE degree from Stan ford University in 1976 With HP since 1973 Carl has worked on a variety of Products inc
45. d the average mass flow through the valve However real valves have nonideal re sponses that can limit system performance and cause con trol instability During turn on the transient response is limited by the inertia of the moving parts viscous drag of the gas inside the valve the spring constant the electrical time constant associated with the system s inductance and resistance and the applied voltage across the coil During turn off the response is only a function of the mechanical properties of inertia viscous drag jet momentum at the nozzle and the spring constant However a finite time is needed for the magnetic field to decay to a point where the magnetic force can no longer hold the valve spring in the on position This time is related to the amount of energy stored in the coil and it is proportional to the inductance and the drive current For turn on the coil needs to be driven with a high cur rent but for turn off faster speed is attained if a low drive current is used It was found that a current of 50 milliam peres was required to guarantee that the valve would ac tuate but stored energy in the coil created unacceptable turn off delays on the order of several milliseconds To reduce the stored energy in the coil a brass disc is inserted between the valve spring and the armature When the valve is energized the air gap in the magnetic path never goes to zero since the permeability of brass is the same as that of air
46. e device functions can also be cleared or triggered on command from the controller and can be instructed to respond to local device controls or to equivalent control messages on the loop Familiarity with the HP IB is helpful in understanding the HP IL and many users will recognize the strong similarities in the preceding discussion Logically the two interfaces are very close The serial loop structure of the HP IL however causes significant differences at the im plementation level The HP IL interface functions are specified in the same manner as IEEE Standard 488 that is by state diagrams which model the behavior of each function While this method is perhaps difficult for the neophyte to understand the precision and conciseness of this form of specification are very difficult to achieve in other ways Once the serial HP IB concept was established other attributes of the HP IL were filled in The loop structure chosen for the HP IL allows an asynchronous handshake similar to that used for the HP IB An eleven bit message frame provides for retention of the attention command mode when true data mode when false and service request functions of the HP IB Thus the HP IB provided the nu cleus for the HP IL and allowed rapid but safe definition of the functions of the new interface Message Encoding The HP IB has an eight bit data bus and several control lines whereas the HP IL must handle these functions over a single bit serial
47. ed so that it does not error check properly the frame received not as sent FRNS and ORAV bits are both set and the bad frame is loaded into R2 R so the controller s microprocessor can read it The firmware can then choose to retry the transmission or notify the user of an error condition Fig 5 and Fig 6 flowchart the normal talker and control ler responses to the interrupt bits Note that although the flowcharts in Fig 3 through Fig 6 are basically correct some of the details of the firmware interaction have been omitted for clarity HP IL State Diagrams The HP IL protocol is defined in the same way as the HP IB that is with state diagrams for the various interface functions such as controller talker listener service re quest et cetera The state diagrams are all envisaged as independent asynchronous machines operating in parallel However the internal states of the sequential device mi croprocessor program and the sequential PLA driven HP IL interface IC are not at all similar to the state diagrams To explain this apparent difficulty the purpose of the defining state diagrams must be understood They are not Fig 5 Simplified flowchart of the response of a talker on the HP IL JANUARY 1983 HEWLETT PACKARD JOURNAL 21 Copr 1949 1998 Hewlett Packard Co intended as a set of internal design rules They serve only as a precise model of the external behavior of a device on the HP IL The device is treate
48. en design Capillary columns mount in the annular space between the fan guard and the cylindrical shroud Packed columns mount forward of the fan and inside the square shroud The shrouds prevent mixing of controlled air with return air within the column area The fanis a flat blade turning at high speed Spatial Gradient C oa 30 10 0 10 30 50 70 Ambient Temperature C Fig 4 Measured spatial gradient the difference in tempera ture between the 5790A oven temperature sensor and the column space as a function of ambient temperature made without previous thermal conditioning yielded data indistinguishable from that of the later runs which had experienced a rather drastic thermal history The temperature sensor a platinum resistance element is located at the rear of the shroud on one side Fig 4 was made using a second sensor located in the column space about 30 mm forward of the control sensor and on the opposite side of the shroud a total separation of about 165 mm Over a very broad range of ambient temperatures the temperature at the column remained very close to that of the control sensor 130 C Calibration Factory calibration yields an absolute accuracy of 0 05 C at 130 C and a full range 80 to 425 C accuracy of 1 5 C Some applications may require that the most accu rate temperature be at some other value or that the calibra tion be optimized for the positive temperature range
49. eparated into its components The noninteracting components travel at the speed of the gas stream while the interacting components are retarded by various amounts depending on the strength of the interaction The elapsed time between the injection of the sample and the appear ance of a given component at the other end of the tube is called the retention time of that component To make this tube a gas chromatograph there must be a detector at the end of the tube that responds to changes in the composition of the gas flowing through it so that as each compo nent reaches the detector there will be a peak in the detector s voltage output Some device for recording the peaks and measur ing the retention times completes the system This can be as simple as a strip chart recorder and a ruler or as elaborate as a data system serving dozens of instruments The power of gas chromatography as an analytical tool comes from two factors There are many different materials available for use as tube coatings and each of these has somewhat different separating power There are a variety of detectors some of which respond to almost anything that passes through them while others are highly selective With the appropriate combination we can separate and measure almost anything that can be vaporized without decomposition For samples that decompose before they vaporize there is a related technique called liquid chromatography Here the sample is dissolved in
50. erform the operation The user is not involved in any specific system details of the operation and can concentrate on the problem rather than on the system that is solving the problem Local Area Network Operation The second functional area of the HP IL that required further definition was the relationship between the HP IL and the emerging concept of a local area network The local area network typically has a number of equally capable devices contending for access to the physical media while the HP IB and the HP IL use one of these devices the con troller to direct traffic on the interface For some applica tions the local area network operation offers simplicity of software support and operation An example is a system of several smart terminals connected to one mass storage de vice In a local area network environment all terminals have the same support software but in an HP IL environ ment one terminal must keep track of I O operations for the others Rather than change the master slave nature of interface control on the HP IL capabilities are present to allow sys tems like the local area terminal network to be implemented easily In particular devices on the HP IL may asynchron ously generate service request messages With this capabil ity in effect a controller may totally ignore the interface tending its own applications until some device on the loop notifies it that an I O operation is desired The controller then mus
51. es the CLIFCR bit to clear the interrupt and then writes the SLRDY bit so that the following ready for command RFC frame will be passed on Any other message frames that require a response from an idle device will cause the FRAV bit to be set The device s microprocessor reads the control bits from R1 R and the data bits from R2 R If the frame is a command the device executes it and then writes SLRDY The only other type of frame that causes a FRAV interrupt in an idle device is an auto address group AAG message The device s micro processor may respond by reading the frame storing its address bits in register 4 incrementing the frame address bit and retransmitting the modified frame by writing it to Copr 1949 1998 Hewlett Packard Co Listener SLADY CLIFCR R2 W Fig 3 illustrates in flowchart form the response of an idle device When a device becomes an active listener the additional capability needed is minimal A FRAV interrupt is received when a data frame comes in The listener s microprocessor reads it may store it in a buffer and then retransmits it An addressed ready group ARG frame also may cause an in terrupt These frames are merely retransmitted by the lis tener s microprocessor Fig 4 shows the additional flow chart necessary for the listener For devices that are normally the destination of loop messages the primary interaction is with the frame available interrupt The previous disc
52. f varies slightly between the cable end plug and the HP IL module body because of differing loads Both receive bending stress but the cable end plugs have the additional load HP IL Interconnect System by James H Fleming ef om Fig 1 Connectors on the ends of each HP IL cable are different and can only be inserted in their proper receptacles on an HP IL device of insertion and withdrawal and are therefore thicker Most of our charger cord failure data showed that the wires broke right at the end of the strain relief on the plug end and at the transformer case on the other end By adjusting the wire stranding cord material durometer hardness and strain relief material durometer hard ness we were able to achieve the ideal situation of ultimate breakage near the middie of the strain relief The module end of the HP IL cable had the first failure after 4 700 90 degree flexes while the plug end survived 7 100 90 degree flexes The strain reliefs are molded in vinyl with a Shore A 65 durometer hardness Acknowledgments would like to thank Gene Frederick for his tool engineering support in bringing the vendors up to speed Dave Hamilton for quality assurance engineering support and Deby Birdsell for documentation and prototype parts organization James H Fleming Jim Fleming received two BS de grees from Oregon State University one in engineering 1961 and one in business administration 1962 With the exception
53. g the difference between two pressure readings drift aging and a F 2 gers Psensor 0 50 100 150 200 Time ms Fig 6 Timing sequence for a typical control cycle JANUARY 1983 HEWLETT PACKARD JOURNAL 37 Copr 1949 1998 Hewlett Packard Co Producing the Electronic Flow Controller The successful operation of the electronic flow controller re quires that a number of key specifications be met These specifi cations include precise dimensional and system constraints in the handling and movement of parts Meeting these specifications presented a challenge to the whole manufacturing department and the fabrications and manufacturing engineering groups in particular An example of that challenge is the valve shown in Fig 9 on page 39 which has a required nozzle orifice diameter of 0 009 0 0002 inch Traditional fabrication methods of drilling and reaming cannot accurately or repeatably produce such an orifice so a new method using electric discharge machining was de veloped Upper Plate WOOT ALY SSS WA Lower Plate Pressure Transducer Po Fig 1 Pressure transducer temperature changes in the pressure transducer do not af fect the flow measurement but to obtain the necessary accuracy and repeatability a high quality pressure trans ducer with very low mechanical nonlinearity and hys teresis had to be developed Transducer Design The transducer consists of t
54. gether For example the point to point structure of RS 232 C CCITT V 24 suggests a star network Fig 1a However this structure is not practical for portable applications because it requires the system controller to have a separate connector for each device In addition to the added cost this would tie up all the T O ports in a small device such as the HP 41C that users might want to use for other accessories The parallel bus structure Fig 1b of the HP IB is much more inviting since only one port or connector per device is required However the electrical design problems are more troublesome Each device s interface output must be able to drive a large assortment of system configurations ranging from one other device connected by a short cable to as many as thirty devices located some distance away The cost and power requirements are too great for portable battery powered devices The system architecture that resolves these difficulties is a unidirectional loop Fig 2 Each device has only one interface connector with two sockets IN and OUT Each output drives only one input regardless of the number of devices connected in the system The electrical design problem becomes much simpler longer distances between devices are possible and the power to drive the interface is minimized and shared among all of the devices Low cost two wire cable allows a distance of up to 10 meters between devices on the loop and work is progressing on a
55. h packed and capillary columns and is available either as Option 140 149 for new 5880A GCs or as Model 19306A B C for addition to an existing 5880A GC Two flow controller modules can be installed in the GC and operate simultaneously controlling four independent streams of carrier gas Design Goals The table below is a summary of the design goals that were established for the electronic flow controller Usable gases are hydrogen helium nitrogen air and argon Carrier Gas Supply Sample Injection Port Gas Flow Control Column Detector methane and the values shown are independent of the gas used Flow Mode Pressure Mode Absolute Accuracy 2 of reading 2 of reading 10 100 ml min 34 620 kPag Repeatability 0 2 of reading 0 2 of reading 10 100 ml min 34 620 kPag 0 450 ml min air with 590 kPag inlet pressure and no load restriction 100 kPag Dynamic Range 0 to head pressure minus 100 kPag Pressure Drop at 60 ml min Flow rates are calculated in milliliters per minute and pressures are calculated in kilopascals kPa where 1 psi 6 8947 kPa Design Details A block diagram of the electronic flow controller is shown in Fig 3 The local microprocessor decides which variable is to be controlled based upon whether the setpoint is for flow or pressure It then compares the actual value with the set point to generate an error term A control algorithm uses the error term to mod
56. he 5790A GC described in the accompanying article is an attempt to provide better control of column not oven temperature than has ever been available The goal is toletthe column perform up to its full capabilities so that distinctly different becomes small enough to eliminate all but one candidate And that of course is that Fred W Rowland Returning to schoo after serving in the U S Air Force for four years Fred Rowland received his BA de gree in chemistry from the University of Buffalo in 1958 and his PhD in polymer chemistry from the Polytechnic Institute of Brooklyn in 1963 With HP since 1966 he s been an applications chemist an R amp D product manager a training man ager and a technical writer He s authored a dozen magazine articles and all or part of three books and is a member of the American Physical Society and the American Association for the Advancement of Science Fred is a native of Buffalo New York and now lives in Kennett Square Pennsylvania He s married has three children coaches youth soccer and serves as data processing director of the local county fair of setpoints called a method Eight such methods can be stored in a battery supported CMOS memory and called into action as required For some specialized work a multiramp oven tempera ture profile may be required A method specifies only a single temperature ramp but each method is cap
57. he lateral channel stop implant Fig 1c similar to an n channel process field implant Another dose of boron in this manner establishes the n channel field thresholds After the photoresist mask is stripped the entire wafer is subjected to an arsenic implant not shown The patterned nitride layer prevents the active regions from being implanted The field oxide is grown in steam Because of the slower diffusion rate of oxygen through silicon nitride oxidation takes place much more slowly for the areas covered by nitride The result is islands of silicon in which active devices will be formed surrounded by regions of thick field oxide Fig 1d The remaining nitride is chemically re moved and a gate oxide 50 nm thick is thermally grown in an ambient of oxygen containing a small percentage of TCE trichloroethylene Polysilicon is deposited Fig 1e by low pressure chemical vapor deposition LPCVD The polysilicon layer is then removed from the backside of the wafer In this manner during phosphorus doping of the polysilicon the backside of the wafer also becomes highly n type improv ing defect gettering The polysilicon is patterned by mask 3 and the exposed regions are plasma etched away Fig 1f The p channel device regions are patterned using mask 4 Fig 1g Photoresist is again used as an implant mask Boron is implanted through the exposed areas of the gate oxide layer to form the p diffused source drain regions The
58. he panel These locations contains such in formation as the present state of the control bits both as transmitted and as echoed line voltage as a percent of nominal power demand by the various heated zones and the presence flags which indicate that the processor is aware that a given heated zone is physically present on the instrument Two memory locations contain the error flags and the error history The error flags show all of the error conditions that exist at a given time the front panel can only indicate two Error history also shows the error flags but this is a latched display which shows all errors that have occurred since the last time it was cleared This is a very helpful tool for trapping intermittents and middle of the night conditions Three diagnostic modes help track down the problem Mode 1 maps the 14 control bits onto the 14 buttons on the lower part of the front panel Each bit is normally low but can be forced high by pressing the corresponding button Mode 2 is the exerciser it tests groups of panel light emitting diodes at a one hertz rate and while each group of LEDs is on it turns the 14 control bits on and off one at a time Mode 3 is a free run mode The normal software is suspended while the processor steps through the entire memory ROM internal RAM external RAM performing a read at each location so that signature analysis trouble shooting can be done Acknowledgments Many people contribu
59. hem always win in any direct confrontation with any other design approach For one thing they easily pro vide the electrical balance and isolation necessary for good noise performance discussed earlier Second they pro vide a very easy way of generating the three level code for the HP IL and require no standby power unlike most active circuits Another advantage is the ability to shift voltage levels with near 100 power efficiency The HP IL nominal voltage levels were chosen at a fairly low level 1 5V typi cal partly to conserve power For example a 100 ohm transmission line can be driven with about ten times less power at 1 5V than at a typical logic level of 5V Fig 8 and Fig 9 show transmitter and receiver waveforms for the circuit of Fig 7 Still another big plus in using the transformers is easy impedance matching It was a strong desire to minimize the circuit parts count by integrating most of the electronics using an LSI process like CMOS The HP IL specification calls for a transmitter impedance of 100 ohms 5 10 It is moderately difficult to achieve on chip impedances lower than 100 ohms in MOS drivers and the tolerances can easily be 30 By using a 3 1 step down transformer as shown in Fig 7 the impedance on the device side of the transformer can be high enough 900 ohms in this case that inexpensive discrete resistors can be used to swamp out the on chip impedance The on chip impedance of 116 ohms 30 58 oh
60. hen there is more than one message frame in transit around the loop at the same time Usually when a frame is being received the input register is empty and the frame is gated through the input buffer directly into the input register Most of the frame decoding is done in the input register Depending on the type of frame and whether the interface IC is configured as HP IL controller talker or listener the frame might be immediately sent out again through the input register mul tiplexer and the transmit encoder or it could be loaded into R2 R There is a third important possibility for the disposition of the frame in the input register If the interface IC happens to be the source of the received frame a talker getting back its own transmitted data frames for example the received frame can be compared to what was transmitted for error checking purposes This is done by shifting out the input register and the output register which contains a copy of the transmitted frame simultaneously through their mul tiplexers into an XOR gate The input and output pointer counters control the three multiplexers that provide the serial to parallel and parallel to serial conversion of HP IL frames Oscillators on the HP IL interface ICs in loop devices are not syn chronized Comparison logic prevents the possibility of the output pointer overrunning the input pointer during an automatic retransmission This requires that the individual bits within
61. her to inject the samples or to modify the flow path through the col umns The 5790A controls a single valve using a valve time setpoint and 16 preprogrammed valve action profiles Methods Atany given time the instrument is controlled by a group column When we repeat the experiment we get the same differ ence but the absolute values have probably shifted a Dit Several factors can cause this change in absolute times Atmospheric pressure is one but the main one is changes in the temperature of the oven where the column resides Recall that one of the factors th S us Separation is the temperature of the column These changes have many causes Room temperature fluctua tions line voltage changes the algorithm used to measure and control the oven temperature and the circuits that implement the algorithm all have their effects Oven temperature control is not simply a matter of holding the temperature constant but of adhering to a programmed temperature versus time profile most often a linear ramp The column temperature profile must be exactly the same from run to run and from instrument to instrument if retention times are to be repeatable to a high degree Oven design is important We do not actually control the column temperature we control the temperature of the temperature sen sor In a poorly designed oven this can be quite different from the column temperature and the retention time data will reflect this Gifference T
62. iagram Copr 1949 1998 Hewlett Packard Co b Output 2 ov et e Vr Output 1 Input o Vr Fig 5 Rise time distortion three level code a Input pulse waveform b Output pulse wavelorms c Circuit block dia gram the HP IL may contain both floating i e battery operated and earth grounded devices The minimum isolation from interface cable to device common or earth ground is specified as 100 pF and 10 MA at 500Vdc This eliminates any ground loop hazards and allows devices to be operated at different potentials For instance an HP IL voltmetermay make small differential voltage measurements with its common terminal several hundred volts above earth ground and the measurement common the same as the circuit common within the voltmeter Each HP IL device transmitter drives only one device receiver This offers certain advantages over a bus type structure The receiver may modify the transmitted mes sage frame waveform e g by filtering attenuating or clamping the signal with no danger of interfering with any other receiver The HP IL takes advantage of this by thoroughly specifying the transmitter while putting almost no restrictions on the receiver except that it reliably detect transmitted signals This is accomplished by specifying several worst case transmitter characteristics that the re ceiver must be able to detect The transmitter is designed to drive a 100 ohm balanced transmission line up to 1
63. ice departments and the 5790A incorporates several diagnos tic modes and self test features that simplify troubleshooting The Column Oven All ovens have a built in problem No matter how good the control mechanisms they really control the tempera ture of the sensing device rather than that of the column Measurements have demonstrated that there can be a sig nificant difference between the conditions seen by the sen sor and those experienced by the column Fig 2 shows the general scheme used in previous chromatographic ovens The fan circulates air throughout the oven and over the sensor and heater The air also con tacts the oven walls and door Since these are heated only by the circulating air they act as heat sinks Thus the tempera ture experienced by the column is generally different from that seen by the sensor This difference is reduced by vio lent mixing of the oven air but cannot be completely elimi nated There will also be gradients across the column space as the cooled air mixes with that controlled by the sensor and heater The 5790A oven is shown in Fig 3 The fan typically a squirrel cage or impeller type has been replaced by a flat blade turning at high speed The fan is surrounded by a wire guard and a cylindrical shroud This type of fan is some what inefficient in moving large volumes of air but it pro duces a region of highly turbulent mixing in the space between the guard and the shroud A second shroud
64. ies where parasitic capacitance de grades transformer isolation a simple low pass filter is used 330 pF capacitors in Fig 7 to filter the outputs of the digital inverter drivers This is necessary because the two inverters generate a common mode pulse of amplitude Vec 2 and a fundamental frequency of 500 kHz with har monics out to very high frequencies A true differential analog driver would eliminate this need for filtering but also would require more complexity and power Equally important was the need to be immune to exter nally generated EMI Our practical experience has shown that power line transients along power cords in close prox imity to the HP IL cables were the most severe sources of EMI that could be expected to be encountered in typical applications For this environment the HP IL defines its own test for susceptibility A two meter power cord is placed parallel to the HP IL cable at a distance of 1 cm The power cord is then subjected to transients with short rise times 5 ns and damped sinusoids The test setup is in tended to represent a rather severe application where HP IL cables and power cords from calculators instruments small appliances and other devices are grouped together on a lab bench or desktop Much data exists regarding the amplitude rise time and frequency of occurrence of trans ients but this is dwarfed by the number of opinions regard ing acceptable performance criteria After much study we
65. ify the duty cycle of a pair of valves causing the controlled variable to change until it equals the setpoint To control flow and pressure the electronic flow control ler must communicate with its host the 5880A Five times Fig 1 Schematic representation of a gas chromatographic system A carrier gas under pressure moves a vapor sample from the injection port through the column where the sample is separated into its components The detector converts the amount of sample reaching it to an electrical signal which is recorded as a function of time Different components of the sample reach the detector at dif ferent times and are seen as peaks in the record JANUARY 1983 HEWLETT PACKARD JOURNAL 35 Copr 1949 1998 Hewlett Packard Co per second the GC sends flow or pressure setpoints to the controller and receives actual values and status informa tion The electronic flow controller also tells the 5880A if the current setpoints exceed their user definable limits Flow and pressure programming are accomplished by hav ing the 5880A increment the appropriate setpoint linearly with time The electronic flow controller sees a new set point every one fifth second and controls to that value Sensing of actual pressure is done by the capacitive pres sure transducer outlined in Fig 4 The transducer consists of a small fixed volume cell whose base is connected to one side of a parallel plate capacitor An inductor is
66. ing an unlisten command to disable previously desig Device Functions Device dependent messages talker or interface messages controller Interface Functions State Linkages Decoder Encoder HP IL in HP IL out Interface Functions R receiver FL remote local D driver AA automatic address AH acceptor handshake Po power down SH source handshake PP parallel poll controller oc device clear T talker or device trigger L listener Do device dependent SR service request command Fig 3 HP IL functional partitions Copr 1949 1998 Hewlett Packard Co nated listeners This would be followed by a listen address command to make the device that has the matching address the active listener Then the talk address command is sent to specify which device is to supply the data This is followed by a special message to begin the data transmission The talker intercepts this message and replaces it with the string of data bytes for the listener s After the last byte of data the talker sends another special message back to the controller indicating completion and the controller takes over and replaces that message with its next command tothe system In addition to the basic controller talker and listener capabilities there are other interface functions to handle handshaking of messages into and out of each device A device can use two different methods to notify the control ler that the device needs attention Th
67. le replica of the desired circuit pattern is imaged through a series of mirrors and projected on the photoresist coated wafer as shown in Fig 4a The resulting image quality is shown in Fig 4b A 2 5 um minimum linewidth with 0 4 um tolerance can be registered to within 1 5 wm of previous layers across the entire 100 mm width of the wafers all values are 3o statistical range The minimum linewidth and registration accuracy de termine the minimum device spacing while the width tol erance sets the variability of electrical device characteris tics During the photoresist exposure partially coherent light predominantly composed of three wavelengths and emitted from a high pressure mercury arc lamp impinges on the multilayered structure of the wafer photoresist and any deposited or grown materials The illumination inten Copr 1949 1998 Hewlett Packard Co sity varies through the thickness of the photoresist because of standing wave reflections of the three wavelengths be tween the top and bottom surfaces of the resist layer The layer thickness is adjusted so that intensity minima lower than the contrast threshold of the photoresist do not occur at the bottom surface The result is less scum unexposed and therefore undeveloped resist at the bottom of devel oped areas Photoresist is predominantly composed of larg polymeric compounds Proper pri necessary to retain a consistent photosensitivity xpos
68. letely asynchronous with respect to each other This makes it possible for de vices of widely different speeds to communicate on the HP IL without difficulty For example many types of frames may be retransmitted by a device after it receives only one bit The remaining frame bits are retransmitted as soon as they are received but at the speed of the device s transmitter electronics not at the speed of the received frame which could be slower or faster Without asynchro nous bits the device would have to wait for all eleven bits in a frame before beginning retransmission to guarantee prop er bit timing If every device on the loop did this the HP IL speed degradation would be phenomenal Two level codes generally require one or more start bits to establish a timing reference For bit asynchronous operation the start bit s would have to be tacked on to every informa tion bit The resulting bit density degradation would be clearly undesirable Perhaps the biggest advantage of a three level code for the HP IL is the ability to detect significantly distorted signals using fairly simple and inexpensive receiver circuits while 1S i See ee ae See Cem 3 Control Bits 8 Data Bits maintaining a high degree of reliability To illustrate just one example of this let s investigate the effect of detector threshold voltage variations in a situation where pulse rise and fall times are a significant percentage of pulse width Fig 4 shows the w
69. log amplification or very ov sv Vro ov 15v Vr ov 1 5V Amplitude depends on load impedence Fig 8 HP IL transmitter waveforms for a logical one bit in the circuit of Fig 7 Copr 1949 1998 Hewlett Packard Co SS MX hey RE S7 ov o7 57V Vao a 0 7V Fig 9 HP IL receiver waveforms for a logical one bit in the circuit of Fig 7 low level comparator circuits Both options are generally higher in cost and use more power at the pulse frequencies used in the HP IL Electromagnetic Interference From the HP IL project s inception a major concern was the radiation of EMI The relatively long interface cables great antennas the lack of any chassis ground and our experience with other products all supported this concern Of five common noise reduction techniques grounding shielding filtering isolation and balancing we chose to concentrate on the latter three mainly because the HP IL does not have the luxury of earth grounds in most products The objective was to minimize the level of any common mode signal relative to earth ground on the two wire inter face and assume that a differential signal would generate electromagnetic fields that would cancel at any significant distance away from the cable more than a few centimeters By their isolating nature the pulse transformers do an ex cellent job of rejecting frequencies below about 10 MHz For the higher frequenc
70. luding the HP 3000 Com puter the HP 91 97 Calculator power supply the optical wand for the HP 41C and most recently the HP IL Heis married has a son and lives in Corval lis Oregon He is interested in white water kayaking nordic and alpine skiing and boardsailing and plays soccer during his lunch hour A CMOS Integrated Circuit for the HP IL Interface by Steven L Harper NDOUBTEDLY THE MOST IMPORTANT judge of the Hewlett Packard Interface Loop HP IL system is the end user However the device designer is probably very near this level of importance also Unless the designer sees the HP IL system as capable and friendly from a design viewpoint the designer is not very likely to create a product that shares these attributes This requirement together with other critical needs of very low power consumption low cost and small physical size make the hardware design decision for the HP IL inter face a fairly straightforward one A CMOS LSI circuit Fig 1 is the only technology that effectively satisfies all of the above objectives Hardware Architecture The eight bit microprocessor has become almost a uni versal controller for the tiny digital systems used in small instruments or peripherals For this reason it made sense to us to design the HP IL interface IC with an eight bit data bus that can mate directly with most common microprocessors In this way the HP IL interface simply becomes another compo
71. m handling without fallout but low enough to prevent damage if pulled out sharply by the cord typically withstanding about two pounds of force The connector system that was ultimately chosen Fig 1 is manufactured by two major companies These are interchanga ble in production and are of comparable quality The contact systems were machine tested and no failures were found after over one million insertion withdrawal cycles It should be pointed out to other potential users of this type of contact that the design and mechanical tolerances of the plastic housings are critical to the reliability of the system HP IL interconnect cables were initially made of the same mate rial used in charger cords but it was felt that these kinked too easily and the material did not perform well during the flex testing Therefore we changed to a vinyl with a lower Shore A durometer hardness of 60 70 and changed the wire stranding from nineteen Strands of 36 AWG copper to twenty six strands of 38 AWG tinned copper An interesting problem arose after switching to the softer durometer hardness cable jacket We had been attempting to maintain a characteristic impedance of 100 ohms in the two conductor cables but when the Shore A hardness was lowered the dielectric constant increased causing the characteristic impedance to be closer to 120 ohms This was corrected by changing the conductor center to center distance from 1 98 mm to 1 52 mm The strain relie
72. more than 20 kilobytes per second each frame contains one byte of data Furthermore the loop could contain as many as ten of these no extra delay devices before the data rate would begin to suffer While such devices could certainly be built with existing technology the HP IL interface integrated circuit see article on Page 16 trades off this maximum performance for somewhat lower cost This leads immediately to the next important question How fast would the HP IL be if it were limited only by the existing interface IC and not by any added software delays Once again the two device loop example is useful except that the devices now use the real HP IL interface IC as opposed to a hypothetical one The sequence of events would proceed more or less as follows After the data byte is written to the talker s HP IL chip there is a 4 us delay before transmission of the bits starts The frame takes 46 us to be sent and then the listener delays 7 us before passing the byte to its microprocessor The listener now retransmits the frame which again has a 4 us delay followed by a 46 ps transmit time After the frame is received at the talker there is a final 34 us wait while error checking is done before the following frame can be sent The grand total is 141 microseconds per frame which trans lates to just over 7 kilobytes per second Because the active While it is rare for a product division of Hewlett Packard to sell the componen
73. ms per inverter adds to the discrete resistance of 766 ohms 1 to generate a loop impedance of 98 ohms 5 sufficient to satisfy the specification As shown above transformers make it possible to use very simple digital circuits for the transceivers The design shown uses diodes in the receiver to convert the three level signal to two ground referenced digital signals with a minimum of signal loss The relatively high receiver load impedance of 15 kilohms reflects to 810 ohms on the inter 14 HEWLETT PACKARD JOURNAL JANUARY 1983 Low Pass Filter for EMI ESD Transient Protection A Sr om 27 esp Transient Protection Fig 7 Schematic of one im plementation of the HP IL elec tronics face is intended to be high enough to minimize signal attenuation 1 dB in this case while being low enough to discharge parasitic capacitances sufficiently fast This de sign approach provides sufficiently large signals to the receiver so that relatively low turns ratio transformers can be used to step up the voltage to allow detection by easily integrated in CMOS Schmitt trigger circuits with typical digital thresholds of 2V to 3V Pulse transformers with high turns ratios generally have poor rise time and overshoot characteristics Therefore a lower level signal at the detec tor circuits e g achieved by removing the receiver diodes and or reducing the receiver resistance values would very likely require either active ana
74. must respond to a message loop speed suffers because of the serial nature of this handshake process This is commonly the case for command messages To alleviate this problem the se quence for commands is modified somewhat P Commands are required to be immediately passed on by all devices This permits the loop devices to execute a command more or less in parallel The return of the com mand message to the controller does not indicate that the devices are ready for another command in this case Con sequently after each command the controller sends a ready for command RFC message which must be held by Table HP IL Control Bit Coding c2 c1 co Message Class 0 End of Service Data Record Request 1 0 0 Command 1 0 4 Ready 1 1 Service Identify Request JANUARY 1983 HEWLETT PACKARD JOURNAL 5 Copr 1949 1998 Hewlett Packard Co each device in turn until that device is ready When the RFC message returns to the controller the next command can be sent Functional Definition It is unusual for a development project to begin with a fully formed functional definition It is even more unusual for that definition to remain relatively unchanged through out the development Yet the HP IL development followed just such a stable path The reason for this stability was the HP IB standard The use of the HP IB model for the HP IL allowed several different groups to proceed in an orderly and efficient manner while developing products tha
75. n the marketplace The only significant tradeoff was speed and as it turns out the primary limit to speed is not the HP IL electronics but the microprocessor based devices talking to the HP IL see box on page 7 The choice of interface media was a very critical decision with conventional cable and fiber optics leading the race and wireless radio control a distant third possibility Al though a wireless interface was appealing practical con siderations eliminated it early After a thorough investiga tion fiber optics was removed from contention primarily because of cost and power consumption limitations The final product is a careful blend of balanced two wire cable inexpensive zip cord for short distances shielded twisted pair for long distances transformer coupling in most HP IL products an innovative encoding method three level self clocking and maximum use of a low power large scale integrated circuit technology CMOS Shown in Fig 1 is the HP 82160A interface to the HP 41C an example of an HP IL product where the cost size and power objectives become visibly obvious Fe THE INITIAL CONCEPTION of the HP IL Encoding Without the luxury of extra interface lines for clocks or handshake signals most interfaces and mass storage de vices use some form of self clocking codes Some common examples are Manchester Miller and delta distance codes Their common trait is encoding logical
76. needs But the trend is de nitely towards capillaries and particularly toward the fused silica capillary The Identification Problem Gas chromatographs are often pressed into service to identify the components of 2 sample mixture However all they can say about the identity of a particular peak is that it takes so many minutes to pass through the column under the given analytical conditions Fig 1 shows a typical chromatogram with the retention time of each peak This single number the retention time tells the analyst very little about the nature of the substance represented by the peak so various ancillary techniques are used to identify it The most powertul of these is to use a GC to prepare the samples for amass spectrometer The mass spectrometer yields direct information on the chemical structure of the sample supplied to it but it must have a pure sample Mixtures produce a mass of overlapping data that cannot be sorted out Fortunately the gas chromato graph does a superb job of preparing pure samples Each peak consists of a single substance and the amount of material in a GC peak is usually much more than the mass spectrometer requires A composite instrument incorporating a GC as the front end of a mass spectrometer is the most powerful identification tool avail able to the analytical chemist There is one problem mass spectrometers are expensive Thus the gas chromatograph which costs quite abitlessand is already
77. nent in a device s microprocessor system This approach provides two important advantages The abilities of the device s microprocessor can be effectively shared between the device functions and the interface func 16 HEWLETT PACKARD JOURNAL JANUARY 1983 tions for lower cost less power and smaller size Perhaps equally important is the flexibility of this design While the time critical portions of the HP IL protocol can be executed quickly by the logic on the interface IC most of the protocol can be contained in the microprocessor s firmware This approach reduces cost and at the same time makes it rela tively easy to incorporate changes to enhance capability or speed or to correct problems Somewhere in the neighbor hood of 1000 bytes of microprocessor code is required to support the HP IL functions for most typical devices having the ability to send or receive data In addition to the eight bit bidirectional data bus com mon to microprocessors the interface IC also has the more or less standard complement of control lines A RESET input allows external power on circuitry to set the entire inte grated circuit to a predetermined state when power is first applied There are three address REGISTER SELECT inputs which select one of eight control and data registers to send or receive on the data bus External address decoding cir cuitry drives the CHIP SELECT input so that the HP IL inter face circuit appears as a block of eight memor
78. ns of communication through the data bus to the de vice s microprocessor are prominent in the block diagram of Fig 1 Note that some of these registers are really two separate registers one that can only receive data from the bus and one that can only send its data out on the bus The read only portions are loaded within the interface IC and the write only sections send their data to or control other internal logic only This technique saves address space for the microprocessor and eliminates the need for an extra address pin R1 W refers to the write only part of register one for example and R2 R similarly indicates the read only half of register two Virtually all communication from the device to the HP IL and vice versa is initiated by read or write operations exe cuted by the device s microprocessor to these eight regis ters No other control lines are necessary to perform this function For example when the microprocessor writes a byte to register two R2 W the interface IC automatically transmits that byte on the loop The interface logic and interface control blocks connect the registers to the external microprocessor This link func tions asynchronously from the loop and the rest of the integrated circuit These blocks provide a simple standard interface to the microprocessor but require an extra inter lock and synchronization circuit If the microprocessor were to read a register at the same instant it was being JANUARY
79. odak Microelectronics Seminar Proceedings October 20 21 1980 San Diego California 2 H Nielsen and D Hackleman Some Illumination on the Mechanism of Silicon Dioxide Etching presented at the Fall Elec trochemical Society Meeting Detroit Michigan October 1982 paper abstract 180 3 K H Zaininger and F P Heiman The C V Technique as an Analytical Tool Solid State Technology May 1970 p 49 Copr 1949 1998 Hewlett Packard Co Norman L Johnson A native and lives in Corvallis Orego outdoor activities particularly camping esides his interest in farming volunteer fireman and on the David E Hackleman A native of Coos Bay Oregon David Hackleman attended Oregon State University and received a BSEE degree in 1973 He continued his studies at the University of North Carolina and eamed a PhD degree in chemistry in 1978 He then came to HP and before assuming his current responsibility as a project manager of MOS lithography and plasma etching R amp D worked on the ICs for the HP 85 Computer and portions of the CMOSC process His work has sulted in eighteen technical articles papers and invited lectures David is a a member of the IEEE the American Chemical Society and the American Radio Relay League and is a Member at Large for the Portland Oregon section of the Elec trochemical Society Since 1979 he has given an annual lecture on semiconductor technology at the U S N
80. ontrol cycle is shown in Fig 6 and applies to either flow or pressure control Initially the inlet valve is activated and the outlet valve deactivated Carrier gas flows from the source into the pres sure sensor Since the outlet valve is deactivated prevent ing flow out of the sensor pressure inside the sensor rises After a predetermined period of time the inlet valve is deactivated stopping the flow of gas and creating a static condition in the sensor After the pressure equilibrates a reading Pigh is taken and stored by the microprocessor Next the outlet is activated while the duty cycle valve remains deactivated Carrier gas flows out of the sensor and into the load for a fixed period of 25 milliseconds After this time the outlet valve is again deactivated A second pressure measurement is taken Pyow and sent to the microprocessor The sequence is repeated five times per second This is a sufficiently high frequency for the control system to sense and respond to fluctuations in source pressure or load pres sure in the time frame in which they occur A fast cycling frequency also assures that pressure perturbations do not occur at the detector In typical applications with 30 ml min flows the pressure perturbations at the transducer are 15 kPa peak to peak but no disturbance can be seen at the detector because of the pneumatic filtering effect of the injection port and column Since the mass flow measurement is made by takin
81. or with control algorithms optimized for this purpose and a number of convenience features that allow the chromatog rapher to use the instrument efficiently At the same time it is fully capable of using packed columns when desired With capillary columns retention time reproducibility of 0 005 minute is possible Vier ANY ANALYTICAL LABORATORY and nn SISO ut Fig 1 The HP 5790A Gas Chromatograph is designed for operational simplicity and high retention time reproducibility Its features include an advanced oven design a large digital display easy setpoint control storage of setpoint methods memory protection stopwatch valve control and built in diagnostics 30 HEWLETT PACKARD JOURNAL JANUARY 1983 The 5790A offers accurate oven temperature control from near ambient to 425 C in 1 C increments and temperature programming with 0 1 C per minute resolution Propor tionally controlled intake and exit vents provide smooth near ambient temperature control Cryogenic cooling to 80 C is optional The 5790A can be controlled by an external computer via its RS 232 C serial communications port Instrument set points system status stored analysis methods and run times can be monitored and modified Analog outputs are provided for recording and for input to integrators such as the HP 3390A Reporting Integrator Serviceability has not been neglected in the 5790A Many users of chromatographs have their own in house serv
82. or contributors to failure This pro ject was no different until consideration was given to the impact that a poor design or an incorrect choice of contact system could have on the success of this new interface standard This design problem was attacked by several engineers as the interface system was being defined Prototype connectors ranged from reworked charger plugs to fiber optic links Finally the connector system came into the critical development path of the seven or so HP IL products The most recent prototype con nectors had provided a means to interconnect the products under development but did not satisfy the rapidly developing list of wants from the HP divisions designing HP IL products These wants included a Cable plugs to fully engage each other with tactile snap Cable end plugs to fully engage the device panel receptacle with tactile snap Both genders of contacts to have maximum recess for mechan ical and electrostatic discharge protection Ability to add a third contact set to the center position for future ground shield requirements Mechanical tolerances to allow compatibility between at least two full sets of multicavity injection molding tools including consistent tactile snap At least two fabrication sources for the contact system Capability of enduring at least 2 000 insertion withdrawal cy cles with no mechanical or electrical failures Plug retention to be great enough to allow normal HP IL syste
83. polysilicon pattern protects the active p channel de vice gate region from the implant creating self aligned gates The n channel device regions are defined by mask 5 ina very similar manner Fig 1h Phosphorus is implanted using the photoresist as an implant mask A short oxidation cycle at this point produces a thin but very defect free oxide layer over the p regions n re gions and polysilicon A phosphorus doped oxide film is deposited as the intermediate insulator By using an ele vated temperature this oxide is softened and flowed to ensure smooth steps for subsequent metal coverage Photoresist is applied and mask 6 is used to define the contact areas Contacts are chemically etched through the phosphorus doped oxide to the p diffusion n diffusion and n polysilicon regions Fig 1i A silicon aluminum alloy is sputtered onto the wafer and patterned using mask 7 and wet etching Fig 1j The wafer is then passivated by a layer of plasma deposited silicon nitride Finally openings to the bond pads are plasma etched through the nitride using mask 8 not shown Low Power Consumption A calculator such as the HP 11C Fig 2 may operate for about one year on a single set of batteries The calculator s standby current is so low that batteries may be replaced JANUARY 1983 HEWLETT PACKARD JOURNAL 23 Copr 1949 1998 Hewlett Packard Co SiaNs Thin Stress Rellet Oxide n Silicon Subst
84. present in the lab is often used alone to identity sample compo nents In this case the chromatographer uses whatever prior knowledge is available One seldom has to consider the entire universe of organic chemistry One does not expect for example to find streptomycin in a sample of floor polish And while it s true that retention time can never yield an exact identification it can Certainly eliminate a lot of possibilities Anything whose retention time on the same column under the same conditions is distinctly different from that of the unknown can be rejected Now we come to the crux of the matter Distinctly different is a variable criterion It depends on how precisely we can measure retention times and on how precisely we can distinguish between different retention times Modern integrators easily measure the times to a milliminute and can be pushed further if the need arises but time resolution is of little use unless the measurement can be repeated at will A good capillary column fused silica of course will separate two compounds whose retention times differ by only 0 14 minute at 30 minutes this is actually part of the checkout test for one HP perform a two point calibration 130 C and 330 C which adjusts both the absolute accuracy and the slope of the calibration curve The factory calibration can be restored by reentering the original parameters Valve Programs Many analyses require valve operations eit
85. ps most of it out through a vent while the remainder passes into the column Unwanted chemical activity in the column has been a problem from the beginning Packed columns were initially made of stain less steel tubing Glass although fragile was used when the samples interacted with the stainless steel The support material with its enormous surface area which was needed to spread the active material out for good contact with the gas could also interact with the sample Many deactivating treatments have been tried but no one has achieved a support that is truly inert to all sample types Capillary columns eliminate the support completely Only the wall activity remains Stainless steel nickel glass and more exotic materials have been used in the continuing search for inertness Fused silica columns introduced by HP in 1979 finally seem to give what the chromatographer has been looking for a Fig 1 Part of a chromatogram of a gasoline sample analyzed on an HP 5880A Gas Chromato graph using a fused silica capillary column The numbers are retention times in minutes 32 HEWLETT PACKARD JOURNAL JANUARY 1983 Copr 1949 1998 Hewlett Packard Co high resolution column in which the only chemical activity is wi the user chooses to incorporate Packed columns are still in use and wil undoubtedly continue to be used for reasons of tradition they do the job standard procedures and a few specialized
86. r to what the devices on the HP IB do but how they do it is very different The differences between the HP IL and the HP IB and the details of the design and operation of the HP IL are discussed on pages 3 through 22 of this issue Our cover photograph shows our art director s conception of an HP IL system in a briefcase A little artistic license has been taken while all of the devices shown can operate on the HP IL not all are battery powered and briefcase portable Another in our series of articles on processes used at HP to produce custom integrated circuits begins on page 23 This process is called CMOSC for complementary metal oxide semiconductor version C It s used by HP s Corvallis Oregon Division to produce ICs for HP Series 10 handheld calculators This issue also carries two articles on gas chromatographs from HP s analytical instruments division in Avondale Pennsylvania When a sample is injected into one of these instruments it is mixed with a stream of carrier gas and transported through a heated tube called a column To ensure accurate results the column temperature and the carrier gas flow rate and pressure all have to be accurately controlled The article on page 30 describes a new gas chromatograph Model 5790A that gives much better control of column temperature than previous instruments While the 5790A is designed for high volume industrial and clinical use the 5880A Gas Chromatograph is HP s top of the line research quality in
87. racterized by more than 35 million device operat ing hours at 70 C A continuing audit of CMOSC products at elevated temperatures insures against any change in device reliability Sixty monitors are used to help control the fabrication process These range from distortion and focus monitors of the projection aligners to etch rate tests and charge inclu sion measurements thp ee GRAPHICS Coed CRASS m ao wazne 11 A2 2 Gavusi ae up currentivoltage characteristic force the mA batteries at th tor system By combining a p well low resistance substrate and using con latched state architecture wit servative inputoutput circuit designs a value of I1 greater This level of latch up hardness is sufficient to protect a calculator system from an 500 mA was achieved see Fig 7 measurable electrical disturbances Electrostatic discharge ESD is anothe sat danger to handheld systems Fortunately ESD susceptibility and latch up hardness are linked High values of 11 usually mean low susceptibility to ESD damage If oxide integrity is poor this may not be the case The CMOSC input out capable of withstanding ESD transients This is well above any level the circuit put circuits are in excess of 4 kV will normally experience once placed into the calculator system Summary The first integrated circuit using the CMOSC process was produced in January 1981
88. rate _ a 9 Boron Implant High Energy Boron implant LILILIIIL RS RS ESS SRE R co Fig 1 Cross sectional views of ee the CMOSC process a Active areas are defined by plasma etch o ing a nitride layer mask 1 b Low Energy Boron Implant TILL Phosphorus Implant dlhiditiiiidiis Photoresist is used to mask p well implant mask 2 c Mask 2 is used again to mask the lateral channel stop implant to avoid subthreshold leakage current d Field oxide is grown by local oxida tion after the lateral channel stop implant e Nitride layer is stripped after field oxidation and polysilicon layer is deposited f Polysilicon definition mask 3 forms a self aligned gate and is used as mask for source drain im plantations for p channel devices and n channel devices g Photo resist mask 4 is used to define p source drain regions during pWell c h Oxide Pa J d 0 e 0 without fear of information loss during replacement CMOSC circuits have an extremely low standby leakage current of 5 to 10 nA To realize such a low leakage current the CMOSC process has some critical design rules For example the distance from the edge of the contact hole to the edge of the active region dimension a in Fig 3a is carefully controlled Leakage characteristics were op timized by improving several process techniques through characterization of the growth
89. s also the firmware s responsibility When a parallel poll enable command PPE is received the device s microprocessor must make sure that the device is an active listener If it is then the least significant bits of the PPE command are decoded and put into register 3 Now the interface IC is ready to respond to parallel poll messages identify IDY frames The actual response to the parallel poll that is entering the active state PPAS of the state diagram is an automatic function of the interface IC When an IDY frame is received the appropriate bit in the frame is modified according to the information stored in register 3 the parallel poll register The automatic retransmission of this frame by the interface IC represents the transition back to the standby state The move back to the idle state from the standby state is once again the responsibility of the device microprocessor s Send Next Command Ready or Identity Frame Error Message to User or Retry Fig 6 Simplified flowchart of the response of a system con troller on the HP IL 22 HEWLETT PACKARD JOURNAL JANUARY 1983 PPE s LACS ACDS Pons a PPU ACDS a PPD LACS ACDS Messages DY Identity PPE Parallel Poll Enable PPD Parallel Poll Disable PPU Parallel Poll Uncontigure b Interface States PPAS Parallel Poll Active State ACDS Acceptor Data State PPIS Parallel Poll idie State DTAS Driver Transter State PPSS Parallel Poll Standby State
90. s written to R2 W The interaction of the interface IC status the received frame and the interrupts is quite complex Table I is a complete summary Taken as a whole this appears rather formidable However when the microprocessor firmware designer starts to design code for the talker function for example it will be found that a relatively friendly subset emerges from the complexity of Table I The protocol used in the HP IL is based on the HP IB and so the mnemonics used in Table I are generally familiar to HP IB users Register 2 is the data register The eight data bits of the received message frame are loaded from the HP IL into the read only part of the register When the frame is transferred to the device s microprocessor another frame can be loaded from the input register into R2 R Also after the data bits of the frame to be sent by the talker or controller are placed in R2 W the interface IC transmits the frame over the loop The information to allow the device to respond automati cally to parallel poll is contained in register 3 A positive response is enabled only when both the parallel poll status bit PPST and the parallel poll enable bit PPEN are set If the parallel poll polarity bit PPPOL is set to one whena positive response is enabled the proper bit in the identify frame is set to one as the frame is retransmitted If PPPOL is zero a negative response PPST 0 PPEN 1 will set the bit in the identify frame This allows
91. strument The article on page 35 discusses the design of a precise new electronic flow and pressure controller for the 5880A On page 32 Fred Rowland gives us some basic information about gas chromatography R P Dolan ographe Arvid A Danielson e Illustrator Nancy S Vanderbloom e European Production Supervisor Henk Van Lammeren 2 HEWLETT PACKARD JOURNAL JANUARY 1983 Hewet Packard Company 1983 Printed in U S A Copr 1949 1998 Hewlett Packard Co HP IL A Low Cost Digital Interface for Portable Applications The Hewlett Packard Interface Loop is a bit serial interface bringing many capabilities formerly reserved for much larger computer systems to the growing repertoire of portable computers and handheld calculators by Roger D Quick and Steven L Harper gan to perceive the need for a low cost low power digital interface standard Progress in integrated cir cuit technology had allowed development of small low cost but fully functional instruments calculators and computers The small size of these products allowed them to be considered portable and many were capable of being battery operated The cost to add a standard interface to these devices could be small but only if the interface were compatible in physical size and power consumption The existing applicable interface standards in 1976 were the HP IB Hewlett Packard Interface Bus HP s implemen tation of IEEE Standard 488 and RS 232 C CC
92. t get involved but only for a temporary period to do a specified transfer Thus for many applications the HP IL can model the operation of a local area network with only a small amount of overhead time and software Interface Components Of course the HP IL will never accomplish its potential unless there are many different kinds of HP IL devices on the market It is unreasonable to think that Hewlett Packard Company would be either able or willing to supply all of them Therefore an important thrust of the HP IL program is to allow others to design the HP IL into their products By using the HP 82166A HP IL Converter a complete HP IL interface component manufacturers can design de vices for the loop with very little engineering effort The converter is a good solution for devices with relatively low sales volume and where small size low power and low cost are not major concerns When these factors are important however the converter is not the optimum solution Though it requires a much greater engineering invest ment primarily in the design of the device s microproces sor firmware a component level interface to the HP IL is necessary when the size power and cost factors are critical to the product There are three components needed for component level implementation the panel connector the pulse transformer set and the HP IL integrated circuit American St ard Code tor Information interchange Copr 1949
93. t the various interrupt conditions Each of these five bits has a corresponding enable bit in R1 W If the enable bit is set and the proper condition occurs to cause the corresponding interrupt bit in R1 R to be set then an interrupt will be generated on the interrupt request line to the device s microprocessor If the enable bit is not set the interrupt bit functions the same way except that no interrupt is transmitted to the microprocessor The interface clear received bit IFCR is set whenever an interface clear IFC command is received Service request received SRQR is set only in the active controller when a data or identify message frame comes in with the service request SRQ bit set This interrupt resets itself when a frame comes in without the SRQ bit set The frame available interrupt FRAV is generally used to indicate to the active listener that a data frame has been received though there are some other situations where this bit is used When the frame is read from R2 R the bit resets Frame received not as sent FRNS tells the active HP IL controller or talker that the frame that was sent returned incorrectly When this hap pens the bad frame is loaded into R2 R so the device s microprocessor can read it Like FRAV this bit resets when the frame is read Output register available ORAV indicates to the HP IL talker or controller that its frame has returned correctly and the next frame can be sent ORAV resets when the next frame i
94. t would use the new interface While most of the HP IL functional definition relied on the HP IB model two areas required further definition The first of these centered on the concept of friendliness which differs according to the type of user To a laboratory en gineer friendly typically means the ability to tailor the operation of an instrument or interface to the engineer s specific needs using as few commands as possible How ever if necessary the engineer wants access to the system s lowest control level to be able to twiddle bits to achieve a desired result Most HP IB implementations allow this level of control At the other end of the user spectrum is the average operator of the consumer calculator This user often does not want to learn anything about the operation of the system that is providing solutions Forcing this user to learn about address and control codes to achieve a desired result is a deterrent to the use of a system Added Interface Functions To allow this kind of friendly use some other interface functions which have no counterpart in the HP IB were added to the HP IL definition Portable systems are often battery powered and conserving that power is usually very important HP IL devices can implement a power down function if needed so that the HP IL controller can com mand a device to enter the powered down state and cause it to return to full power With a real time clock and a wakeup function added to
95. tarted as one operator and now is a three shift operation Before construction of the fabrication area began scale models were used to find optimum locations for the equip ment in the clean room Work flow safety particle con tamination and supervisory feedback were all considered The improvement in the efficiency of clean room space is demonstrated by Fig 6 Fewer individuals can perform more operations in less space and less time fora net savings compared to the older bulk CMOS process of roughly a factor of 5 Reliability At each step of CMOSC the acceptance criterion is no visible defects Requiring complete coverage of all contact holes by metal Fig 1j and locating passivation openings only above metal pads over field oxide removes several Copr 1949 1998 Hewlett Packard Co 104 Bulk 4 CMOS Process E cmosc Process 014 0 Work Area Labor Process Time per per per Wafer Out Water Out Wafer Out Special cleaning pathways for ionic contamination techniques at gate oxidation and polysilicon gate deposi tion help lower the defect density Oxide defects decrease reliability A special intermediate oxide layer traps Group I metal contaminants such as sodium before they can enter the sensitive gate oxide re gion Use of such a layer is not common in most CMOS processes giving CMOSC circuits an intrinsic reliability advantage The effects of using these process steps have been cha
96. ted to the success of this project and we can only name a few To those not mentioned we re grateful for your help Product manager Ann Lawrence headed the marketing effort assisted by Ralph Culver and Rod Hougentogler in product support Fred Rowland and Norm Frank wrote the manuals Karl Wagner did the mechanical design while Bernie Hedges was our right hand man during electronic de velopment Antoinette Brossman deserves special thanks for her printed circuit layout work Ed Warren did design 34 HEWLETT PACKARD JOURNAL JANUARY 1983 work on some of the detector systems Manufacturing en gineers were Dick Kruppa and Jeff Fromm who received his law degree during the project and is now with HP s Corpo rate Legal Department Dave Clouser and Dennis Havens provided test procedures and manufacturing documenta tion respectively Douglas H Smith Doug Smith is a section leader at HP s Avondale Division He first joined HP Laboratories in 1968 as a research en gineer He has authored papers on analytical instrument system design and low level signal processing is an inventor on the basic printer plotter pa tent for HP integrators and GC systems and has served as project leader for various analytical instruments for another firm Born in Los Angeles he received his BS and MS degrees in computer science from the University of 1 California at Berkeley in 1964 and 1967 Now living in West Grove Pennsyl vania Doug is married h
97. the HP IL controller to receive the logical AND or the logical OR of the responses of multi ple devices in a single bit in the identify frame The three low order bits in register 3 determine which bit will be modified in the identify frame Also in register 3 are two read only bits that indicate when the output register is empty ORE and when a re ceiver error has occurred RERR This is caused by the presence of a sync bit in the middle of a message frame Register 4 is the loop address register The five least significant bits contain the HP IL device s assigned loop address When an idle device receives a talk or listen com mand frame for example and the bits in the command frame match the bits in register 4 the device s HP IL inter face integrated circuit interrupts the device s microproces sor so that it can set the appropriate status bit TA or LA in this case If the bits do not match the command does not disturb the device s microprocessor The three high order bits of register 4 and all bits of registers 5 and 6 are scratchpad registers for the device s firmware designer to use for any purpose This data is preserved even when the master clear bit is set and the oscillator is shut off as long as power is continuously applied to the interface IC Register 7 contains the two input flag bits AUX6 and Howiott Packard Interface Bus HP s implementation ot IEEE Standard 488 1978 Interrupt Process Auto Address Fr
98. the state of switches for example The otherread only bits always return ones The write only part of register 7 has only one bit the oscillator disable bit OSCDIS After the master clear bit is set this bit turns the oscillator off or on The other bits are don t cares they can be written as one or zero with no effect on the interface IC Device Interaction with the Interface IC To understand fully the place of the interface IC in the HP IL portion of the microprocessor system of a device it is necessary to delve into the firmware and look at some specific situations A prospective designer will then be able to see how Table I reduces to something more manageable In the case of an idle device the possibilities are few Many types of message frames are automatically retransmit ted on the loop without disturbing the device s micro processor at all Some other frames do cause an interrupt 20 HEWLETT PACKARD JOURNAL JANUARY 1983 Don t Care Some combinations are explained in the text so the table does not necessarily represent all possible don t care states The bit is set high when the specified frame is received and the chip status is as shown but are simply retransmitted without any other response If an interface clear IFC is received the IFCR bit is set causing an interrupt Since the device is already in an idle state however nothing needs to be done to execute this command The device s microprocessor simply writ
99. ts that go into its products separately that is exactly what is happening because of the special need to make the HP IL available to other manufacturers Customers are able to buy not only the connector the trans former and the integrated circuit Fig 4 but also the HP 82166C HP IL Interface Kit complete with documentation and the HP IL Development Module for the HP 41C Pro grammable Calculator The components for the HP IL con verter are included in the kit Hand in hand with this pro gram of selling the HP IL components directly goes the development of alternate sources for these components listener does not retransmit the frame before it has been com pletely received any additional devices will add to the time and degrade the data rate somewhat An idle device using the present HP4L interface IC delays a data frame by 13 us so that three devices on the loop will reduce the speed to about 6 4 kilobytes per second four devices will only support 5 9 kilobytes per sec ond and five will run at 5 5 kilobytes per second As the analysis gets closer and closer to the real world software delays must also be accounted for With a reasonably fast micro Processor and time efficient not necessarily ROM efficient code an extra delay of no more than 50 us could probably be achieved in each active HP IL device At a little less than 250 us per frame the two device loop would have a speed of just over 4 kilobytes per second three de
100. ugh a pair of wires using a floating balanced differential voltage mode of operation This provides good noise immunity and re duces EMI electromagnetic interference Eliminating the need for a system ground avoids the problems often as sociated with ground loops and makes it easy for devices to float with respect to earth ground a feature especially con venient for devices like voltmeters The electronic design of the interface is discussed in the article on page 11 The design of the custom CMOS IC is described in the article on page 16 Functions While size and power considerations required new inter face electronics the functionality of a new interface was a separate question Experience with the HP IB standard has shown it to be flexible but complete Diverse products built to the HP IB standard are able to communicate without anomalies To perpetuate the HP IB functionality in a lower performance serial interface is obviously attractive and it was with this objective that the Hewlett Packard Interface Loop HP IL was created The functions within a device divide logically into two categories device functions and interface functions Fig 3 The device functions are special to each type of device The 4 HEWLETT PACKARD JOURNAL JANUARY 1983 designer can choose and implement these functions in any way considered appropriate Therefore the device func tions in a voltmeter for example will have little similarity to those
101. ure treatment is reful control of coating and drying conditions is necessary Posi tive photoresist acts unfavorably in an oven purged with pure nitrogen forming a tough outer skin which can sub sequently lift and redeposit in a different location during Deposited Intermediate Oxide Grown Oxide Substrate a Fig 2 The HP 11C A calculator representative of the type using the CMOSC process development Therefore clean processed air is used instead of pure nitrogen Development of an image to 0 4 um toler ance using a mask with 0 2 um tolerance requires continu ous control of the concentration and temperature of the developer and the time of development Developer titration and adjustment to 1 are performed frequently The de velopment is done in a batch proc ss an automatic opera tion that includes a nitrogen blanket and recirculating temperature control to better than 1 C Once the image is developed the critical geometries of the silicon nitride island before oxidation and the polys con gate pattern are plasma etched A single wafer parallel plate plasma reactor using SFe as an etchant gas provides reproducible control of the transistor width is land and length gate A typical cross section demonstrat JRNAL 25 JANUARY 1983 HEWLETT PACKARD Copr 1949 1998 Hewlett Packard Co Front Surface Mirror Front Surtace Mirrors Aperture Mask A0
102. ussion regarding idle devices and listeners illustrates this With talkers and con trollers however which are usually the sources of loop messages the emphasis shifts to the output register available interrupt ORAV This interrupt does not merely indicate that the message frame has been transmitted It is used to notify the device s microprocessor that the full loop handshake has been completed In the case of a data frame sent by a talker this means that the frame has been transmit ted has been received and retransmitted by the active lis teners so that they are all ready to receive another data frame has returned to the talker and has been error checked and found to be correct Only at the completion of this sequence does ORAV go true When an HP IL controller generates a command the frame is sent and in turn is automatically retransmitted by all devices each retains a copy of the command and begins executing it the com Process Command Frame Set SLADY lt gt Send Error Frame ETE Send Next Data Frame Fig 4 Simplified flowchart of the response of a listener on the HP IL mand returns to the controller where it is error checked the controller s interface IC automatically sends the ready for command frame which is retransmitted by each device when it finishes executing the previous command and the RFC returns to the controller s interface IC which then sets ORAV When a frame is garbl
103. vices would operate at 3 8 kilo bytes per second four at 3 6 and five at 3 5 Probably the easiest way to determine the data rate of a real system is simply to total the delay times of the individual devices involved These times must be measured from the end of the received frame to the end of the frame transmitted through the device Naturally this value will vary somewhat depending on whether the device is acting as a talker or a listener and what type of data is being transmitted but an average value is still useful For the HP IL interface integrated circuit without extra software delays the delay is around 70 us When the assumed software delay is added the number goes to 120 us An HP 85 Personal Computer with the I O ROM and HP IL interface can achieve a frame delay of roughly 300 us The HP 82161A Digital Cassette Drive takes 600 us per frame for a transfer of less than one 256 byte record but increases to an average of 2600 us per frame for very large blocks of data because of the record gaps on the tape The slowest device is the HP 41C Programmable Cal culator with its bit serial microprocessor at about 5000 us delay per frame A little computation then indicates that the combination of the HP 41C and the cassette drive can achieve a data rate of 175 bytes per second for short transfers and about 130 bytes per second for longer blocks of data An HP 41C talking to an HP 85 can run at a little less than 190 bytes per second If a
104. wo ground metal plates witha nominal air gap of 0 045 mm and a capacitance of 28 to 45 pF at 0 kPag The moving plate approaches the fixed plate as the pressure is increased to achieve a minimum gap of 0 025 mm at 700 kPag The fixed plate is ground flat within 0 0005 mm while the moving plate is flat within 0 005 mm Electronic Design Because of the digital nature of the 5880A GC it was decided that the sensor outputs would be frequencies which can easily be converted to digital form A modified Colpitts oscillator also known as a Clapp oscillator was chosen because of its good frequency stability over the large operating range A schematic drawing of the oscillator is shown in Fig 7 The frequency of oscillation is 38 HEWLETT PACKARD JOURNAL JANUARY 1983 However the heart of the electronic flow controller is the pres sure transducer The design is based on a parallel plate capacitor with a small gap that varies with pressure Fig 1 The fabrication process must assure that the transducer responds linearly with pressure The most important component in the transducer is the dia phragm which provides the link between the pneumatic input and the capacitive output see Fig 2 The diaphragm has to approxi mate an ideal circular plate so that its motion is within calibratable limits To ensure that those limits could be met on a routine basis existing processes had to be modified and statistically charac terized Statisticall
105. xtension for the HP IL will be the design of implementations with substantially higher transfer rates yet compatible with current designs Future implementations will also become even more friendly in both the low level control and the transparent operation senses Today even the smaller computers require the user to plan activities taking into account the computer and its transportability Future computers and computer exten as casually as today s calculators People not because thi Acknowledgments The HP IL interface program was a joint venture of two pr tgr lett Packard the Instrument Group and the Personal Computer Group This program was a good example of two groups cooperating effectively to pro duce an outstanding new product The HP IL standard is a credit to all who worked on it and special thanks go to Bill Kay Roy Barker and Chung Tung for perceiving the need for the HP IL and for supporting the joint venture at the Steven L Harper 1 Steve Harper is a graduate of Brigham Young University He received the BSEE degree in 1971 and the MSEE degree in 1972 then joined HP His n contributions have included work on in es sirument calibration software and q rmware for the HP 01 Calculator A Watch and serving as a project man i ager for the HP IL Steve is co author of abook The HP IL System An Introduc tory Guide to the Hewlett Packard Inter face Loop and is named co inventoron y
106. y Stanford California November 1980 n Substrate Fig 1 Cross section of CMOS inverter structure What Is Latch Up Fig 2 Equivalent circuit for CMOS inverter 4 Latch Up Current l3 o Voo Vss vi Fig 3 V characteristic for circuit in Fig 2 segment liquid crystal display driver a clock and an analog low battery detector circuit Acknowledgments Successful development of the CMOSC process would not have been possible without the dedicated efforts of the employees of HP s Corvallis Division and discussions with people at other HP divisions The CMOSC production staff headed by Jim McMahon and the process engineering group under Gary Castleman are responsible for the dramat ic increases in efficiency offered by CMOSC Susan Swehosky extracted logical meaningful phrases from our very rough draft Without the rapid aid of Ellen Tappon and her associates in HP s Corvallis Components Operation Physical Analysis Lab problems such as the contact etch effect discussed in the text would never have been solved as quickly and effectively Rapid effective maintenance was brought into the CMOSC area by Hugh Van der Huel and his staff The quality assurance staff helped by performing long term failure tests and are continuing to do a quality audit on the CMOSC process 28 HEWLETT PACKARD JOURNAL JANUARY 1983 References 1 R Hershel et al Registration Monitor for 1 1 Aligners K
107. y addresses or input output ports to the device s microprocessor A WRITE or READ input gates the contents of the data bus into or out of the interface IC An INTERRUPT REQUEST line indicates to the microprocessor that the HP IL interface circuit needs Copr 1949 1998 Hewlett Packard Co Fig 1 Block diagram of HP IL interface CMOS integrated circuit This IC has an eight bit bidirectional data bus for easy connection to most common microprocessors attention Beyond those connections that interface to the device s microprocessor are a number of pins necessary to support the HP IL interface IC The power and ground lines need a standard 5V supply There are two loop data inputs and two loop data outputs which connect to the pulse transformers and other discrete components that adapt the logic level signals to what is required on the loop There are also two connections for a parallel LC circuit to control the fre quency of the on board oscillator at 2 MHz Two general purpose flag inputs are provided along with a special flag that is sampled only when power is applied and indicates to the integrated circuit that it either is or is not incharge of the entire HP IL system SYSTEM CONTROLLER The last pin on the integrated circuit s 28 pin dual in line plastic package is an external oscillator input primarily used for testing purposes Various parts of the eight registers that are the main mea
108. y significant numbers of parts were fabricated so that defects in the design and the process could be uncovered The final fabrication process is a combination of machining lap ping electric discharge machining and special polishing The finished parts are specially packaged to keep them clean and Protect them from damage Diaphragm 47 SAP 0 0005 in to Fig 2 Details of diaphragm where Lo Co Cg and C are components defined in Fig 7 The inductance portion of the tank circuit is a high Q low temperature coefficient 0 65 H inductor It plays a very important part in assuring frequency stability with time and temperature The output stage of the transducer electronics is a cas code amplifier which uses two RF transistors to minimize reverse gain This type of amplifier prevents extraneous signals at the output from feeding back to the oscillator and affecting its operation It is important to have a constant load on the oscillator so that impedance changes whichcan cause frequency variations are not seen by the circuit Typ ical frequency noise at the output is at most 100 Hz regard Sensor Co Lo Ce Fig 7 Oscillator used in the capacitive pressure sensor Copr 1949 1998 Hewlett Packard Co Sensor Oscillator Output Signal fm Frequency Duty Cycle Fig 8 Digital processing system of the electronic flow controller less of cable orientation or cable vibrations The controller

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