THE RAND TABLET: A MAN-MACHINE GRAPHICAL
`COMMUNICATION DEVICE™
`M. R. Davis and T. O. Ellis
`The RAND Corporation
`Santa Monica, California
`
`Present-day user-computer interface mecha-
`nisms provide far from optimum communica-
`tion, considerably reducing the probability that
`full advantage is being taken of the capabil-
`ities of either the machine or of the user. A
`number of separate research projects are un-
`derway, aimed at
`investigating ways of im-
`proving the languages by which man communi-
`cates with the computer, and at developing
`more useful and more versatile communication
`channels, Several of these projects are. con-
`cerned with the desien of “two-dimensional” or
`“graphical”? man-computerlinks,
`
`Early in the development of man-machine
`studies at RAND, it was felt that exploration
`of man’s existent dexterity with a free, pen-
`like instrument on a horizontal surface,
`like
`a pad of paper, would be fruitful. The concept
`of generating hand-directed,
`two-dimensional
`information on a surface not coincident with
`the display device (versus a “light pen”) is not
`new and has been examined by others in the
`field. It is felt, however, that the stylus-tablet
`device developed at RAND (see Fig. 1)
`is a
`highly practical
`instrument, allowing further
`investigation of new freedoms of expression in
`direct communications with computers.
`
`|
`
`The RAND tablet device generates 10-bit
`x and 10-bit y stylus position information.
`It
`
`is connected to an input channel of a general-
`purpose computer and also to an oscilloscope
`display. The display control multiplexes the
`stylus position information with computer-
`generated information in such a way that the
`oscilloscope display contains a composite of the
`current pen position (represented as a dot) and
`the computer output. In addition, the computer
`may regenerate meaningful track history on
`the CRT, so that while the user is: writing, it
`appears that the pen has “ink.” The displayed
`“ink”is visualized from the oscilloscope display
`while hand-directing the stylus position on the
`tablet, as in Fig. 1. Users normally adjust
`within a few minutes to the conceptual super-
`position of the displayed ink and the actual
`off-screen pen movement. There is no apparent
`loss of ease or speed in writing, printing, con-
`structing arbitrary figures, or even in penning
`one’s signature.
`
`To maintain the “naturalness” of the pen
`device, a pressure-sensitive switch in the tip
`of the stylus indicates “stroke” or intended
`input information to the computer. This switch
`is actuated by approximately the same pres-
`sure normally used in writing with a pencil, so
`that strokes within described symbols are de-
`fined in a natural manner.
`
`* This research was supported by the Advanced Research Projects Agency under contraet No. SD-79. Any views
`or conclusions should not be interpreted as representing the official opinion or policy of ARPA or of the RAND
`Corporation.
`
`Valve Exhibit 1030
`Valve Exhibit 1030
`Valve v. Immersion
`Valve v. Immersion
`
`

`

`326
`
`PROCEEDINGS—FALL JOINT COMPUTER CONFERENCE, 1964
`
`
`
`Figure 1. Complete System in Operation.
`
`In addition to the many advantages of a “live
`pad of paper” for control and interpretive pur-
`poses, the user soon finds it very convenient
`to have no part of the “working” surface (the
`CRT) covered by the physical pen or the hand.
`
`The gross functioning of the RAND tablet
`system is best
`illustrated through a general
`description of the events that occur during a
`
`major cycle (220 ysec; see timing diagram,
`Fig, 2). Figure 3 is the system block diagram
`with the information flow paths indicated by
`the heavier lines. The clock sequencer furnishes
`a time sequence of 20 pulses to the blocking
`oscillators. During each of the 20 timing peri-
`ods, a blocking oscillator gives a coincident
`positive and negative pulse on two lines at-
`tached to the tablet.
`
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`30 psec
`
`Major cycle
`
`220 psec
`
`9
`
`2
`
`S psec
`
`5
`
`Figure 2. Timing Waveforms (nsec).
`
`

`

`THE RAND TABLET: A MAN-MACHINE COMMUNICATION DEVICE
`
`327
`
`
`20
`
`
`Clock
`Blocking
`
`
`
`Sequencer
`Oscillators
`
`
`&
`Conirol
`
`
`
`Pen Switch
`
`Filter &
`
`
`
`
`
`
`
`
` Output Register
`
`Low--------- naSteet Interface(UT| 4wne---ed
`
`20 Bits
`
`Figure 3, Graphic Input System Block Diagram.
`
`The pulses are encoded bythe tablet as serial
`(x,y) Gray-code position information which is
`sensed by the high-input-impedance, pen-like
`stylus from the:epoxy-coated tablet surface. The
`pen is of roughly the same size, weight, and
`appearance as a normal fountain pen. The pen
`information is strobed, converted from Gray
`to binary code, assembled in a shift register,
`and gated in parallel to an interface register.
`
`tablet, com-
`The printed-circuit, all digital
`plete with printed-circuit encoding,
`is a rela-
`tively new concept made possible economically
`by advances in the art of fine-line photoetching.
`The tablet is the hub of the graphic input sys-
`tem, and its physical construction and the
`equivalent circuit of the tablet
`itself will be
`considered before proceeding to the system
`detail.
`
`The basic building material for the tablet is
`0.5-mil-thick Mylar sheet clad on both sides
`with 14-ounce copper (approximately 0.6 mils
`thick). Both sides of the copper-clad Mylar
`sheets are coated with photo resist, exposed to
`artwork patterns, and etched using standard
`fine-line etching techniques. The result
`is a
`printed circuit on each side of the Mylar, each
`side in proper registration with the other.
`(Ac-
`curate registration is important only in the en-
`coder sections, as will be seen later.) Figure 4
`is a photo of the printed circuit before it has
`
`been packaged. The double-sided, printed screen
`is cemented to a smooth, rigid substrate and
`sprayed with a thin coat of epoxy to provide
`a good wear surface and to prevent electrical
`contact between the stylus and the printed cir-
`cuit. The writing area on the tablet is 10.24 X
`10.24 in. with resolution of 100 lines per inch.
`The entire tablet is mounted in a metal case
`with only the writing area exposed, as can be
`seen in Fig. 1.
`
`Although it would be very difficult to fully
`illustrate a 1024 X 1024-line system,
`it does
`seem necessary, for clarity, to present all the
`details of the system. Thus, an 8 X 8-line sys-
`tem will be used for the system description and
`
`ae BeHeal
`
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`ausana
`
`Figure 4. Unmounted Printed Circuit.
`
`

`

`
`
`3828 PROCEEDINGS—FALL JOINT COMPUTER CONFERENCE, 1964
`
`expansion of the concept to larger systems will
`be left to the reader.
`
`Figure 5 shows the detailed, printed circuit
`on each side of the 0.5-mil Mylar for an 8 X 8-
`line system. The top circuit contains the x posi-
`tion lines and the two y encoder sections, while
`the bottom circuit has the y position lines and
`the two x encoder sections. It should be noted
`that
`the position lines are connected at the
`ends to wide, code-coupling buses. These buses
`are made as wide as possible in order to obtain
`the maximum area, since the encoding scheme
`depends on capacitive coupling from the en-
`coder sections through the Mylar to these wide
`buses. It should be further noted that the posi-
`tion lines are alternately connected to wide
`buses on opposite ends. This gives symmetry
`to the tablet and minimizes the effect of regis-
`tration errors.
`
`With reference to Fig. 5, at time t, encoder
`pads p,+ are pulsed with a positive pulse and
`pads p,— are pulsed with a negative pulse.
`Pads p.i+ are capacitively coupled through the
`Mylar to y position lines ys, Ys, y:;, and ys, thus
`coupling a positive pulse to these lines. Pads
`Pi- are capacitively coupled to y position lines
`Yi; Yo, Ys, and y,, putting a negative pulse on
`these lines. At time t., encoder pads p.+ and
`p.— are pulsed plus and minus, respectively,
`putting positive pulses on y position lines y;,
`Ys, Ys, and y,, and negative pulses on y position
`
`¥;, and y;. At the end of timet:,
`lines y:, Y2,
`each y position line has been energized with a
`unique serial sequence of pulses.
`If positive
`pulses are considered as ones and negative
`pulses are zeroes, the Gray-pulse code appear-
`ing on the y position wires is as follows:
`
`Vi
`Vo
`Va
`Va
`Vs
`¥s
`y;
`Ys
`
`000
`001
`011
`010
`110
`111
`101
`100
`
`The x encoder pads are now sequentially pulsed
`at times t,, t;, and t., giving unique definitions
`to each x position line.
`
`If a pen-like stylus with high input imped-
`ance is placed anywhere on the tablet, it will
`pick up a time sequence of six pulses, indicating
`the (x,y) position of the stylus.
`It should be
`pointed out again that the stylus is electro-
`statically coupled to the (x,y) position lines
`through the thin, epoxy wearcoat.
`
`If the stylus is placed on the tablet surface
`at a point (x,,y;), the pulse stream appearing
`at the pen tip would be as indicated in Fig. 6.
`This detected pulse pattern will repeat itself
`every major cycle as long as the stylus is held
`in this position. If the stylus is moved,a differ-
`
`
`
`Figure 5. Double-sided Printed-circuit Layout for 8 x 8 System.
`
`

`

`THE RAND TABLET: A MAN-MACHINE COMMUNICATION DEVICE
`
`329
`
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`1 = Encoder pad coupling capacity ~ 5 pf
`Pulses at positionAS4AHF(Xgo ¥5)
`C2=Capacity to adjacent parallel wires in tablet ~ 10 pf
`C3= Capacity fo crossing fines in screen ~ 100 pf
`Ca = Stylus-to-tablet coupling capacity ~ .5 pf
`C5 = Stylus input shunt capacity ~ 5 pf
`R = Stylus input resistance ~ 200 KQ.
`Bere reedyJL_______
`Figure 7. Equivalent Cireuit of Encoder-Tablet-Stylus
`Coupling and Attenuating Elements.
`
`Figure 6. Timing Diagram and Pen Signals for the
`Example 8 x 8 System.
`
`ent pulse pattern is sensed, indicating a new
`(x,y) position.
`
`Since there are 1024 x position lines and 1024
`y position lines, 20 bits are required to define
`an (x,y) position. The actual timing used in
`the RAND system was shownin Fig. 2. Timing
`pulses tz, tes, and t., are additional pulses used
`for bookkeeping and data manipulation at the
`end of each major cycle.
`
`The position lines on the full-size tablet are
`3 mils wide with a 7-mil separation. The code-
`coupling pads are. 16 to 17 mils wide with a 3-
`to 4-mil separation. Figure 4 shows that the
`encoding pads which couple to the lower set of
`position lines (y position lines) are enlarged.
`This greater coupling area increases the signal
`on the lower lines to compensate for the loss
`caused by the shielding effect on the upper
`lines
`(since they lie between the lower lines
`and the stylus pick-up). The encoding pad for
`the two least-significant bits in both x and y
`was also enlarged to offset the effect of neigh-
`boring-line cancellations. With these compen-
`sations, all pulses received at the stylus tip are
`of approximately the same amplitude.
`
`Figure 7 is an illustration of the approximate
`equivalent circuit of the encoder-tablet-stylus
`system, along with typical system parameter
`values.
`It is clear that the values of C, vary
`with encoder-pad size, and the value C, varies
`according to whether top or bottom lines are
`being considered. The value of C, is also de-
`pendent on the stylus-tip geometry and wear-
`coat thickness of the tablet. The signals arriv-
`ing at the input to the stylus amplifier are ap-
`
`proximately 1/300 of the drive-line signals. The
`character of the signals at the stylus input is
`greatly dependent on the drive-pulse rise time.
`
`Figure 8 is an oscilloscope pattern of the
`amplified signals at the stylus output.+ These
`signals are amplified again and strobed into
`a Gray-code toggle. An x bit at t, and a y bit
`at ti; are smaller than the rest. This indicates
`that the stylus tip is somewhere between lines
`and these are thebits that are changing.
`
`Since the final stages of the amplification and
`the strobing circuit are dce-coupled, the system
`is vulnerable to shift in the de signal level. For
`this reason, an automatic level control (ALC)
`circuit has been provided to insure maximum
`recognizability of signals. During the first 180
`usec of a major cycle, the stylus is picking up
`bits from the tablet. During the last 40 usec,
`the tablet
`is quiet—i.e.,
`the stylus is at
`its
`quiescent
`level. During this 40-psec interval,
`the quiescent level of the pen is strobed into
`the ALC toggle. If the quiescent level is recog-
`nized as a zero,
`the ALC condenser changes
`slowly into the proper direction to change the
`recognition (via a bias circuit) to a one, and
`vice versa. For a perfectly balanced system, the
`ALC toggle would alternate between 1 and 0
`with each major cycle.
`
`A Gray code was selected so that only one
`bit would change value with each wire posi-
`tion, giving a complete and unambiguous deter-
`
`+ It will be noted in the oscilloscope pattern of Fig.
`8 that the pulsing sequence is x first and y last. This
`is mentioned only because it is the opposite order of
`that shown in the 8 x 8-line example system discussed
`above; otherwise, it is unimportant.
`
`

`

`330
`
`PROCEEDINGS—FALL JOINT COMPUTER CONFERENCE, 1964
`
`
`
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`
`
`
`
`
`Figure 8. Oscillogram of Pen Signal and Strobe.
`
`mination of the stylus position. Furthermore,
`a reflected Gray code facilitates serial conver-
`sion to binary. The conversion logic for an
`N-bit number, when N is the most significant
`bit, is:
`Binaryy = Grayy
`B; = (Bin A Gs) V (By A G))
`
`.jJ<N
`
`Time-wise, the bits are received from the stylus
`in the order N,...,j+1,j,...,1. When all 20
`bits have been assembled in the shift register,
`they are gated to the output register.
`
`As a new (x,y) value is being converted to
`binary and shifted into one end of the shift
`register, the old binary value is being shifted
`out the other end. This old binary information
`is serially reconverted to Gray and compared
`to the new, incoming Gray value, one bit at a
`time.
`If the old Gray number and incoming
`Gray number differ in more than one bit
`in
`either x or y, a “validity” toggle is set to indi-
`cate an error. If the two Gray-code series differ
`in more than one bit, this indicates that the pen
`has moved more than one line during the 220-
`usec interval. As this is not probable during
`normal usage, it is assumed that an error has
`occurred. If a set of data are determined as not
`valid, the output register is left with its previ-
`ous value, and an “old-value” toggle is flagged.
`
`The binary-to-Gray conversion logic is:
`
`Gy = By
`G; = (B;,; A B;) V (B;.; A B;) -jI<N
`
`the validity check rarely detects
`In practice,
`errors while the pen is in contact with the
`tablet. The pen validity check is used to sup-
`press the display of the pen position as the pen
`is lifted off the tablet.
`
`The logic and clock systems are made up prin-
`cipally with state-of-the-art NOR circuits and
`univibrators. The blocking-oscillator circuit
`shown in Fig. 9 was designed to drive the
`encoder pads. This use of transformer cou-
`pling was found to be important since well-
`matched positive and negative pulses were re-
`quired to obtain proper cancellation at
`the
`tablet surface. The stylus amplifier has a gain
`of approximately 30 db with an additional 30-db
`gain in the principal electronic package.
`
`The total electronic system is assembled in a
`5” X 5” x 19” printed-circuit card cage and
`contains some 400 transistors and about 220
`diodes; however, little attempt has been made
`to minimize the number of components. Also,
`the electronics could be shared with a number
`of tablets in a multiple-tablet system.
`01
`
`Out+
`
`Figure 9. Blocking Oscillator.
`
`

`

`THE RAND TABLET: A
`
`MAN-MACHINE COMMUNICATION DEVICE
`
`331
`
`Display
`scope
`
`DA circuits
`
`
`Tablet
`
`
`
` (20 lines)
`control
` Computer
`
`& buffer
`
`(20 line pairs}
`(20 lines)
`
`Figure 10. Information Paths in Graphic I/O System.
`
`4 Multiplexing
`o
`switch
`
`Figure 10 is a block diagram showing the
`graphic input-output system as used at RAND
`for the evaluation of hardware, human engi-
`neering studies, and investigation of program-
`ming implications. The computer used was the
`JOHNNIAG, a tube machine of the Princeton
`class.
`
`Preliminarystudies indicate that witha great
`amount of care in construction, a 200-line-per-
`inch tablet could be achieved. The resolution of
`this line density would not present a major
`problem; on the other hand, 100 lines per inch
`is adequate for all current intended applications.
`
`It is certainly within the state of the art to
`decrease the major cycle time; however,
`in
`usage at RAND, the 4.5-ke rate has been ade-
`quate. Whenthe stylus is swept rapidly across
`-the surface of the tablet,
`it has been found
`that an average of two or three complete sets
`of position data are obtained for each line. Set-
`ting the multiplexing switch (Fig. 10) to dis-
`play the stylus position on the scope every 10
`msec has proved adequate, and since only 50
`psec are required to display the point, 99.5 per
`cent of the display scope time is left for the
`computer.
`
`The tablet currently is in regular use at
`RAND in studies toward the development of
`on-line graphical programming languages and
`on-line interaction with problem parameters, In
`addition to its use at RAND, several copies of
`the tablet have been supplied to other research-
`ers in thefield.
`
`The tablet has been found to be particularly
`valuable in applications where excellent
`line-
`
`arity and accuracy are important. Normal-
`thickness C.G.S. maps have been placed over
`the tablet to digitize contours by manual trac-
`ing with the pen.
`
`Development of the stylus-tablet device has
`been carried to the point where, we feel,
`it
`represents a practical and economical tool for
`use in many applications. Additional applica-
`tion areas might be served by more development
`effort in directions such as providing for rear-
`projection of images onto the (translucent)
`fet, PT
`AOLL LOL
`Ol ITI
`tablet panel, provision for use of more than
`one sensing element, extension of the surface
`al
`+n
`UL1LITIIOLULIS, CLL,
`
`BIBLIOGRAPHY
`
`1. LicKLIper, J. C. R., and CLARK, W.E., “On-
`Line Man-Computer Communication,” Proc.
`1962 SJCC, 118.
`
`2. Loomis, H. H., Jr., Graphie Manipulation
`Techniques Using the Lincoln TX-2 Com-
`puter (Lincoin Laboratory, MIT, Cambridge,
`November 11, 1960), 516-0017 (U).
`
`3. MaRRILL, T., ef al., “Cyclops—1: A Second-
`Generation Recognition System,” Proc. 1963
`FJCC, 27.
`
`4. Stotz, R., “Man-Machine Console Facilities
`for Computer-Aided Design,” Proc. 1963
`SJCC, 323.
`
`5. SUTHERLAND, E. E., “Sketchpad: A Man-
`Machine Graphical Communication System,”
`Proc. 1968 SJCC, 329.
`
`6. TEAGER, H. R., Private Communication, MIT.
`
`

`

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