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Message preparation timing apparatus4286112
Abstract
An apparatus is disclosed for use with teletypewriter consoles in teleprinter communication networks for providing transmission time information during message preparation; namely, the number of whole minutes of message time plus either the number of characters remaining to the next full minute, or tenths of minutes of additional message time used. Such information enables the user to anticipate and thus optimize message time for which he is charged in a rounding-up charge procedure commonly used in such teleprinter communication networks. A preferred embodiment consists of a microprocessor-based computer for converting each character on a perforated tape to a sub-unit of time corresponding to the appropriate transmission rate of either TELEX or TWX network services. A 6-digit display permits the user to observe the actual number of whole minutes and either number of characters to the next whole minute or number of tenths of minutes already used in addition to whole minutes as he is preparing a perforated tape containing the message to be transmitted at a subsequent time. By merely checking the display, the operator may be continuously apprised of the time in minutes and tenths of minutes, or time in whole minutes plus the number of characters remaining until the next whole minute of message time, based on the characters already punched onto the perforated tape. In addition, in the preferred embodiment the user may preset a minimum on-line time to account for time lost during answer-back and signing-off which does not ordinarily constitute actual message time but which is still charged to the user. A keyboard is provided for selecting the appropriate message rate for either TELEX or TWX and for entering the appropriate sign-on and sign-off additional time for which he is charged. A particularly novel feature of the invention, which precludes the need for modifying a teletypewriter console device with which the present invention is to be used, is a photosensor circuit through which perforated tape passes as it emanates from the tape perforating device connected to the teletypewriter console.
Claims
I claim:
1. An apparatus for use with teletypewriter consoles in teleprinter communication networks for providing transmission time information during message preparation by determining and displaying such information, the apparatus comprising:
means for continuously detecting the number of characters in a teletypewriter message as it is being prepared for subsequent transmission;
means for selecting a message transmission rate index corresponding to the transmission rate to be utilized by said communication network;
means for selecting a pre-set time period corresponding to sign-on and sign-off times for message transmission; and
means responsive to said detecting means, to said index selecting means, and to said time period selecting means for determining and displaying the period of time required to transmit said number of characters.
2. The apparatus defined in claim 1 wherein said means for continuously detecting comprises:
a photoelectric sensing circuit having means for receiving a pulse of incident light upon occurrence of a character generated by said teletypewriter and further having means for generating a pulse signal in response thereto.
3. An apparatus as defined in claim 2 wherein said means for selecting a message rate index comprises:
at least one key on a keyboard comprising a plurality of keys, said key being electrically linked to a digital computer having a memory device for storing, in table format, a plurality of data signals representing message transmission time corresponding to each of a plurality of numbers of characters and for at least one rate of transmission.
4. An apparatus as defined in claim 3 wherein said means for selecting a pre-set time period comprises:
a plurality of numerically valued keys on a keyboard each electrically linked to said digital computer, said digital computer having an additional memory device to store data signals representing numerical time periods.
5. An apparatus as defined in claim 4 wherein said responsive means comprises:
a register for accumulating a count corresponding to the number of pulse signals generated by said sensing circuit;
means in said digital computer for fetching rate data signals from said stored table of data in correspondence to said count in said register and for fetching time data signals from said memory in correspondence to said time period selection;
means in said digital computer for additively combining said rate data signals and said time data signals for generating information data signals corresponding to the period of charge time required to transmit the number of message characters corresponding to said count at said transmission rate, and
a display responsive to said information data signals for continually indicating said period of charge time.
6. An apparatus for use in conjunction with teletypewriter consoles for providing information regarding time of transmission of messages in preparation for subsequent transmission over teleprinter communication networks, the apparatus comprising:
a keyboard having means for selecting one of a plurality of transmission rates each of which corresponds to a known period of time for transmitting a message character;
a message character sensing device for detecting the occurrence of each character being generated and having means for producing a corresponding electrical signal representative of each such occurrence;
a microcomputer connected to said keyboard and to said sensing device, having a register for accumulating a count corresponding to the number of character occurrence signals produced by said sensing device, and having a memory device pre-programmed to store therein tables of message transmission times including at least one table for each transmission rate in said plurality, each such table having a plurality of signal codes representative of said transmission times and arranged in known correspondence to said register count;
said microcomputer being responsive to said rate selecting means of said keyboard and to said accumulating count of said register to fetch from said memory device the particular signal code that is indicative of the time required to transmit the number of characters represented by said character count at the selected transmission rate; and
a digital display device connected to said microcomputer for receiving said fetched signal code and for displaying said transmission time.
7. The apparatus defined in claim 6 wherein said message character sensing device comprises:
a photoelectric sensing circuit having means for receiving a pulse of incident light upon occurrence of a character generated by said teletypewriter and further having means for generating a pulse signal in response thereto.
8. The apparatus as defined in claim 6 further comprising:
means in said microcomputer for generating said signal code in a selected one of a plurality of selectable formats for display in said digital display device, said formats including a first format corresponding to the number of whole minutes and fractional minutes for the required transmission time, and a second format corresponding to the number of whole minutes of transmission time plus the number of characters available before the next whole minute of said message time is achieved.
9. The apparatus as defined in claim 8 wherein said keyboard further comprises means for selecting one of said formats.
10. The apparatus as defined in claim 6 further comprising:
means on said keyboard for selecting numerical value codes corresponding to a pre-set time period which represents the sum of the sign-on and sign-off times for message transmission, and
means in said microcomputer for adding said pre-set time period code to said signal code whereby the sum is displayed by said digital display device.
11. The apparatus as defined in claim 8 further comprising:
means in said microcomputer for generating a real time signal code for display in said digital display device when neither of said first or second formats is selected.
12. In a teleprinter communications network of the type having teletypewriter consoles for transmitting and receiving messages over such a network, and wherein a plurality of consoles each include a tape perforating and reading device for preparing messages for being transmitted, the improvement comprising:
an apparatus for use with said teleprinter consoles that include said tape perforating and reading device, the apparatus having means adapted to continually sense the occurrence of message characters on a perforated tape being generated by said device while a message is being prepared for subsequent transmission and to generate an electrical signal representative of each such occurrence, the apparatus further comprising:
a keyboard having means for selecting one of a plurality of transmission rates each of which corresponds to a known period of time for transmitting a message character;
a microcomputer connected to said keyboard and to said sensing means and having a register for accumulating a count corresponding to the number of character occurrence signals produced by said sensing means, and having a memory device pre-programmed to store therein tables of message transmission times including at least one table for each transmission rate in said plurality, each such table having a plurality of signal codes representative of said transmission times and arranged in known correspondence to said register count;
said microcomputer being responsive to said rate selecting means of said keyboard and to said accumulating count of said register to fetch from said memory device the particular signal code that is indicative of the time required to transmit the number of characters represented by said character count at the selected transmission rate; and
a digital display device connected to said microcomputer for receiving said fetched signal code for displaying said transmission time.
13. The improvement recited in claim 12 wherein said sensing means comprises:
light emitting means producing a beam of light of cross section having dimensions substantially equal to the perforations in said tape;
light sensitive means producing an electrical signal having a parameter dependent upon whether a light is incident thereon; and
structural means supporting said light emitting means and said light sensitive means in spaced alignment and forming a passageway therebetween that is adapted to receive said perforated tape whereby said tape blocks said beam of light except when a tape perforation corresponding to a message character passes through said beam of light.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to apparatus for use with communications-related equipment and more specifically to a calculation device to aid in the preparation of wire service messages which minimizes cost per word to the user.
The preferred embodiment of the present invention is intended primarily for use with circuit-switched public teleprinter networks and more specifically with the teletypewriters that are commonly used for transmitting messages over such networks. It is generally well known that there are two circuit-switched public teleprinter networks available, both of which are operated by the Western Union Company in the United States. These two networks, commonly referred to as TWX and TELEX, both provide means for utilizing teletypewriters to transmit written messages using common phone lines. TELEX and TWX teletypewriters are usually operated in conjunction with punched tape devices that use perforated paper tape to provide the opportunity to prepare and proofread messages before they are transmitted. The teletypewriter and accompanying tape perforater device are typically provided by the system operator on a rental or lease-purchase basis.
TELEX typewriters use a five channel paper tape as the input for automatic sending of messages. The tape code language is called BAUDOT and the transmission rate for TELEX machines is 66 words per minute when automatic equipment utilizes paper tape to send messages. TWX teletypewriters operate at 100 words per minute and utilize an eight channel paper tape that employs a code language commonly referred to as ASCII. The term ASCII stands for American Standard Code for Information Interchange.
In addition to the rental fees charged users for rental of the teletypewriter equipment, the service operators, such as Western Union, ITT, and RCA, charge their user customers on the basis of the amount of time required to transmit the message. In at least one instance, namely, the transmission of TWX system messages, the charge is made in full minute increments by rounding up to the next whole minute the actual time from the moment the receiving party's answer back is recorded to the moment the sender terminates the message. For example, if the total transmission time is 1.1 minutes, the time charged for sending the TWX message will be 2.0 minutes. Clearly, such rounding up to the next whole minute can result in significant additional costs to the user. By way of example, if the user were to send one international TWX or TELEX message per day, this "rounding up" procedure would add about $300.00 per year to the user's bill, assuming 260 working days, a $2.80 per minute billing rate, and a 0.45 probability factor that the message length is randomly distributed between X.1 minutes and X.9 minutes where X is any integer. This figure of $300.00 per year represents the minimum additional expense for time charges resulting from the rounding up procedure but not for time actually used for transmission of a TWX or TELEX message.
2. Prior Art
Although there are patents in the prior art which disclose devices for measuring the time required for sending a message and for measuring the length of the message to be transmitted, none of such prior art devices known to the applicant provides a suitable solution to the above-indicated problem without substantial modification and/or costly interfacing to the existing teletypewriter devices. By way of example, U.S. Pat. No. 2,150,240 to Nichols discloses a complex mechanism for the measurement of time required for the transmission of messages in a printing telegraph system. In addition, U.S. Pat. No. 2,191,798 to McCann, U.S. Pat. No. 2,481,112 to Hanley, U.S. Pat. No. 3,035,765 to Zenner et al, disclose devices relating to the broad concept of counting the time of message transmission and for displaying such time. However, no prior art devices known to the applicant discloses a portable, low-cost, microprocessor-controlled device that can accomodate both TELEX and TWX teletypewriter message systems and which can be added to such teletypewriter systems to help the operator anticipate his on-line time and avoid the aforementioned rounding up charge penalties, but without requiring significant modification to the teletypewriter.
SUMMARY OF THE INVENTION
The present invention substantially overcomes the aforementioned problem by providing the teletypewriter user with message-related information such as a continuous display of the projected "on line" time of the message as it is being prepared, that is, as it is being transformed to punched tape at the teletypewriter. With such continuous feedback of information, it is possible for the user to abbreviate, modify message structure, make format changes, eliminate answer-back operation, or send additional information to take advantage of additional "free" on line time up to the next whole minute of message time. In this way the user can avoid paying for any significant amount of unused rounded up time which would otherwise constitute message time in which no message information is sent, but for which a charge is incurred.
A preferred embodiment of the present invention consists of a microprocessor-based computer for converting each "pulse" corresponding to a character (a single column of perforation code) on the perforated tape to a sub-unit of time corresponding to the appropriate transmission rate of either TELEX or TWX. Thus, by merely checking the accompanying display, the operator may be continuously apprised of the time, in minutes and tenths of a minute, corresponding to the number of characters already punched onto the perforated tape. A keyboard provided in the preferred embodiment also provides for selection of a character mode in which the user can chose to continuously display the number of whole minutes of transmission time already exceeded by the number of characters, as well as the number of characters available to be punched on the tape prior to the next whole minute of transmission time. In addition, in the preferred embodiment to be disclosed herein, the user may preset a minimum on-line time to account for time lost during answer back and signing off which does not ordinarily constitute actual message time, but which is charged to the user. Keyboard means are also provided for selecting the appropriate message rate for either TELEX or TWX depending upon the type of system being utilized for message transmission. In the preferred embodiment herein disclosed, the invention is coupled to the teletypewriter mechamisn by means of a photosensor through which the perforated tape passes as it emanates from the tape perforating device connected to the teletypewriter. Although other coupling schemes that include a device for sensing the number of characters generated on the tape as the message preparation proceeds, would be suitable for use with the present invention the photosensing element of the preferred embodiment illustrates one manner in which the character-sensing signal input to the invention may be provided without requiring modification to the teletypewriter per se.
In addition to the above-indicated novel features of the present invention, the preferred embodiment described below also operates in a clock mode in which the display provides a standard real-time clock readout which may be used to provide useful information when message preparation feedback information is not desired.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide a tape preparation feedback device which calculates and displays the transmission time that will be required to send a message while it is being prepared for later transmission by teletypewriter exchange services such as TELEX, TWX, and the like.
It is an additional object of the present invention to provide means for the user of a teletypewriter exchange service, such as TELEX, TWX, and the like, to more efficiently utilize charged transmission time that would otherwise not be utilized for actual transmission of message information because of a whole minute round-up charge procedure.
It is still an additional object of the present invention to provide a portable low-cost message preparation timing system for operation with a teletypewriter exchange message service and that provides information for maximizing the cost efficiency of later message transmission, but without requiring modification to the teletypewriter per se.
It is still an additional object of the present invention to provide a device for displaying data related to the message time required for the transmission of teletypewriter exchange service information, and which is compatible with both TELEX and TWX paper tape code language formats and with both TELEX and TWX message data rates.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned objects and advantages of the present invention, as well as additional objects and advantages, will be more fully understood hereinafter as a result of the detailed description of a preferred embodiment of the invention taken in conjunction with the accompanying drawings in which:
FIG. 1 is an illustration of the present invention shown in use with a teletypewriter;
FIG. 2 is an enlarged three-dimensional view of a preferred embodiment of the invention;
FIG. 3 is a block diagram illustration of the preferred embodiment of the invention;
FIG. 4 is a schematic diagram of a tape perforation reader used in the preferred embodiment;
FIG. 5 is a schematic diagram of the preferred embodiment of the invention; and
FIGS. 6 and 7 provide a flow chart representation of the computer program routine used in the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIG. 1 there is shown therein a preferred embodiment of the message preparation timing apparatus 10 of the present invention in use with a teletypewriter apparatus of the type previously described. More specifically, there is shown in FIG. 1 a teletypewriter 1 having a keyboard 2 and a tape perforating device 3 from which a tape is shown emanating. In addition to the perforation code previously alluded to, the tape 4 also includes sprocket holes 5. One such hole is aligned with each aligned set of perforations corresponding to a single character of the message to be transmitted by TELEX or TWX phone line service. Tape perforations 5 are especially suitable for use by the present invention because one such perforation occurs irrespective of the nature of the character to which it corresponds. Thus, for example, when a space is typed, which space has no message or code perforations, a tape sprocket perforation will still occur and be counted as a character for purposes of the present invention. This, of course, is appropriate because even spaces take a character time period to be transmitted and thus enter into the calculation of the transmission time charge as previously discussed.
As shown further in FIG. 1, message preparation timing apparatus 10 is adapted to respond to perforations 5 by means of a reader 70 through which the tape 4 passes as it emanates from perforater 3. Reader 70 is connected to the main housing or chassis of the invention by means of a suitable cable 71. Although the invention may be adapted to operate on battery supplied power, the preferred embodiment utilizes an AC to DC converting device 90 which in turn is adapted to be plugged into a suitable AC outlet and to generate the appropriate 5 volts DC for the described embodiment which is made available to the circuits within apparatus 10 by means of a suitable cable 91.
Aside from the reader 70 and power supply 90 and their corresponding connector cables 71 and 91 respectively, the entire invention 10 may be housed within a calculator-like assembly or housing 11 which is shown in enlarged view in FIG. 2. As shown in FIG. 2 the exterior of housing 11 provides the user with a six-digit display 40, a specially adapted keyboard 50, and a light emitting diode array 60. Display 40 includes six eight-segment digits identified from left to right in FIG. 2 as 41, 42, 43, 44, 46, and 47, respectively. The display 40 provides the user with useful information in all three modes of operation of the invention, namely, the character mode, the timing mode, and the clock mode. In the character mode the left three digits, namely, digits 41, 42, and 43 display the number of whole minutes already equal to or exceeded by the corresponding total number of characters sensed by reader 70; and the right-most three digits, namely, digits 44, 46, and 47 display the number of characters remaining to be added to the perforated tape before reaching the next whole minute of message time as calculated by the microcomputer of the present invention and based upon the standard rates for TWX and TELEX messages in which one minute of transmission time corresponds to 660 characters and 300 characters, respectively.
In the timing mode, the display provides a running indication of elapsed corresponding transmission time for the number of perforations of characters sensed by reader 70 and is displayed in minutes and tenths of minutes. The number of minutes are displayed in the three digits 41, 42, and 43 and the number of tenths of minutes are displayed in digit 47. Digit 46 displays a constant decimal point and digit 44 is left blank to provide the spacing between the two sets of numbers. Thus it is seen that the character and timing modes of the present invention provide two distinct means for informing the user, that is the tape preparer, with information necessary to determine, during the preparation of the perforated tape, precisely how much message time he will be charged for in either the TELEX or TWX mode of transmission.
A third mode of operation, namely, the clock mode, provides a conventional clock readout in display 40 which may be selected whenever the message preparation timing function of the present invention is not required.
Keyboard 50 provides numerical value keys 0 through 9 similar to numericl value keys provided in conventional calculator devices. However, a number of additional keys unique to the present invention are also provided; namely, three keys corresponding to the three previously described modes of operation, namely, a clock timing and character mode key; two keys for selecting the transmission rate, namely, a TWX key and a TELEX key; and three additional function keys, namely, a START key, a STOP key, and an ENTER key.
LED display 60 includes a plurality of light emitting diodes each assigned to a particular function indication providing the user with additional information regarding the status of the invention; namely, indications of clock, timing, and character mode selection; TWX and TELEX transmission rates and the functions ENTER and STOP as well as an additional indication of whether an error has been generated by some false or unacceptable entry at the keyboard. The particular purpose and function of each key of keyboard 50 and of each LED of array 60 will be more fully understood hereinafter in conjunction with the detailed description of the structure and operation of the invention.
The detailed structure of the present invention may be more fully understood by reference to FIGS. 3 through 5 of which FIG. 3 is a block diagram in which it may be seen that the present invention is a microcomputer or microprocessor-based system comprising an encoder 20, a microcomputer 30, a display 40, a display buffer 45, a keyboard 50, an LED array 60, a tape reader 70, a signal conditioner 80, and a suitable power supply 90. In a preferred embodiment of the present invention, microcomputer 30 is a complete 8-bit microcomputer on a single MOS integrated circuit chip which provides 2048 bytes of read only memory (ROM), 64 bytes of scratch pad random access memory (RAM), a programmable binary timer, 32 bits of input/output, and a single +5 volt DC power supply requirement. In the preferred embodiment of the present invention it has been found preferable to utilize the MK3870 microcomputer.
Keyboard 50 is connected to the microcomputer 30 by means of an encoder 20 such as a National Semiconductor model MM74C923 20-key encoder which provides an internal register which in effect remembers the last key pressed even after the key is released.
Another input to the microcomputer 30 is a signal derived from tape reader 70, which signal passes through signal conditioner 80 to provide the microcomputer with a character signal each time a sprocket perforation 5 is sensed by the tape reader. Microcomputer 30 provides output signals to a display buffer 45 which is in turn connected to both LED array 60 and display 40 for strobe operation of those indicating devices in a manner to be more fully understood from the detailed schematic diagram of FIG. 5 which will be described below. One additional block in FIG. 3 is power supply 90 which provides DC voltage power to all of the circuits of the invention. In addition, a 60 Hz. timing signal derived from the AC line source is supplied by the power supply 90 to the microcomputer 30 to provide the time base for the clock mode of operation which will also be more fully described below.
The remaining detail structural features of the present invention will now be described in conjunction with the circuit diagrams of FIGS. 4 and 5.
Referring now to FIG. 4 it will be observed that a reader circuit 70 of a preferred embodiment of the invention consists of a light emitting diode 71 in series with a resistor 72, both of which are in parallel with a photosensor 73 which is, in turn, in series with a resistor 74. When the light emitting diode 71, acting as a light transmitter, is activated by current flowing through bias resistor 72, an infrared light beam is emitted. If any object is located between LED 71 and photosensor 73, such as semi-opaque paper tape 4, the beam power incident at photosensor 73 is substantially attenuated or entirely eliminated. In this mode photosensor 73 is in an off state and the signal at the output terminal is at a voltage level substantially equal to +5 volts DC. However, as a perforation 5 on paper tape 4 passes in front of the beam emitted by LED 71, the beam reaches photosensor 73 without attenuation causing photosensor 73 to turn on thereby pulling the output signal voltage available at the output terminal toward ground potential.
It will of course be recognized that the passage of perforated tape 4 through the beam emitted by LED 71 is relatively slow in an electrical period sense. Accordingly, the variation in output voltage at the output terminal of reader 70 consists of a series of pulses of relatively slow rise and fall times that may vary significantly with the mechanical action of the tape perforater 3 in advancing tape 4 as it emanates from the perforater. For this reason, the output signal from the tape reader 70 is modified by signal conditioner 80 which, as will be hereinafter more fully understood in conjunction with FIG. 5, acts on the output pulses provided at the output terminal of reader 70 to provide cleaner pulses of relatively short rise and fall times. One such clean pulse is generated for each tape perforation 5 sensed by reader 70.
Referring now to FIG. 5 which is a detailed schematic of the invention, it will be seen at the top-most portion thereof that the output terminal of reader 70 is connected to the negative input terminal of a comparator 81 which forms part of the signal conditioner 80. The positive input terminal of comparator 81 receives a positive voltage derived from the voltage dividing resistor network consisting of resistors 82 and 83 which are connected in series between +5 volts DC and ground potential. This positive voltage is adjusted so that it is equal to the output voltage of the reader when no perforation is being sensed so that the output signal at terminal 84 of comparator 81 is substantially zero volts DC. However, when the reader output potential is reduced to substantially zero volts DC, which occurs when a perforation 5 passes through the beam of light transmitted by LED 71 of FIG. 4, the output voltage at the negative input terminal of comparator 81 suddenly drops to close to zero volts DC and the voltage difference between positive and negative terminals input to comparator 81 produces a positive going output signal at terminal 84.
As shown in FIG. 5, the output terminal 84 of comparator 81 is connected to the clock terminal of a D-type positive edge triggered flip flop 85 of which the preset and data terminals are electrically connected to +5 volts DC through a suitably valued voltage drop resistor 86. Those familiar with the electronics art and more specifically with logic circuits will recognize that with the preset and data terminals tied permanently to a high voltage level, the positive going edge of the signal applied to the clock terminal of flip flop 85 causes the Q output to generate a high or positive voltage level whenever the clear terminal is also high. In effect, therefore, flip flop 85 constitutes a single bit register which stores the reader pulse conditioned by signal conditioner 80 for presentation to microcomputer 30 to indicate that a sprocket hole 5 on tape 4 has passed through the beam in the reader 70, at a suitable point in the cycle of operation of microcomputer 30.
Still referring to the top-most portion of FIG. 5 it will be seen that keyboard 50 is electrically connected to encoder 20. Each key thereof is schematically represented by the intersection of an electrical row, coded Y1 through Y5, and an electrical column, coded X1 through X4, respectively. Each such intersection, is, in addition, numbered on the keyboard schematically wherein numbers 0 through 19 represent the twenty keyboard contacts of keyboard 50. Encoder 20 is adapted to produce a binary representation at its output terminals, A through E, corresponding to the appropriate combination of row (Y) and column (X) intersection for the particular key that has been depressed. At the data available terminal DV on the left side of encoder 20, a data available output voltage goes to a high level when a valid keyboard entry has been made. The data available output voltage returns to a low level when the entered key is released even if another key is depressed. The data available output signal will return high to indicate acceptance of the depressed key after a normal debounce period. The signal at the data available terminal DV is transferred to the clock terminal of a second positive edge triggered flip flop 25 of which the preset and data terminals are also connected to +5 volts DC through resistor 86.
Thus, flip flop 25 also acts as a single bit register which stores the data available signal and provides a high level at the Q output terminal available to the microcomputer 30 whenever the clear terminal of the flip flop 25 receives a high voltage signal generated at the strobe output terminal of microcomputer 30 as shown in FIG. 5. A high output voltage, available at output terminal Q of flip flop 25, informs microcomputer 30 that a new key has been depressed for which a corresponding binary code is available at output terminals A through E of encoder 20, which code is presented to the microcomputer at terminals 0, 1, 2, 3, and 4 of port P4. In a preferred embodiment of the invention, flip flops 25 and 85 are provided on a single dual D-type positive edge triggered flip flop chip such as a Texas Instruments Model 74LS74.
Thus, it is seen that the keyboard 50 and reader 70 combined with suitable encoder and conditioning circuits, respectively, provide the primary data inputs to microcomputer 30. Additional inputs to the microcomputer include a timing signal derived from the alternating current line frequency which is applied to the EXT/INT terminal, the +5 volts DC voltage level applied to the VCC terminal, and ground potential applied to the GND and TEST terminals. In addition, a crystal of suitable characteristics and associated capacitor circuit are connected to terminals XTL1 and XTL2 to provide suitable timing control (1 MHz.) for microcomputer operations. The line frequency signal derived from the AC source provides a 60 cycle per second reference pulse for the clock operation of the invention and is input at the EXT/INT (External Interrupt) terminal of microcomputer 30.
The output signals derived from microcomputer 30 from ports P1 and P5 are indicated in the lower portion of FIG. 5 and are applied to display 40 and LED array 60 as described below. It will be recognized by those familiar with the art to which the present invention pertains that the individual LEDs of LED array 60 are electrically interconnected as a seventh digit of display 50 and that the entire assembly is activated for appropriate display by means of a combination of segment signals derived from microcomputer port P5 and strobe signals derived from microcomputer port P1. This combined segment and strobe activation of the 6 digits of display 40 and the equivalent seventh digit comprising the LEDs of array 60, is performed in a well known manner which need not be described in detail herein except to point out that the segment and strobe signals are amplified by means of circuits within display buffer 45. Buffer 45 includes a plurality of non-inverting buffer drivers 61 embodied within a pair of TTL circuit chips such as Texas Instruments Model 7407 hex buffer drivers. In addition, display buffer 45 includes a plurality of inverter buffer drivers 62 connected in series with resistors within resistor network 63 through which the segment signals pass to the digits of display 40 and the LEDs of array 60. The plurality of inverter buffer drivers 62 may be embodied within a pair of hex inverter buffer driver TTL circuit chips such as Texas Instruments Model 7406.
The structural configuration of the invention will now be fully understood as a result of the above description of FIGS. 1 through 5. However, the manner in which the invention operates upon the input and output data signals described above, depends upon the binary data contained within the 16 Kbits of memory within microcomputer 30 which constitute the program contained therein. The program is disclosed herein in full by means of a combination of a detail listing in Table I as well as a representative flow chart thereof comprising FIGS. 6 and 7. A detailed description of the instructions employed in the program, as well as of the operation and implementation of a suitable microcomputer 30, may be found in the book entitled "MOSTEK 1979 Microcomputer Data Book" by Mostek Corporation, June 1979; and more specifically at pages 327-432 thereof.
TABLE I
__________________________________________________________________________
PROGRAM LISTING
ROM ROM INSTRUCTION
ADDRESS
CODE
IDENTIFICATION
CODE OPERAND
COMMENTS
__________________________________________________________________________
0000 1A A0 DI
0001 70 CLR CLEAR I/O PORTS
0002 B0 OUTS P0
0003 79 LIS 9 CLEAR D-F/F AND DISPLAY
0004 B0 OUTS P1
0005 70 CLR CLEAR SCRATCH-PAD
0006 0B A1 LR IS, A
0007 70 CLR
0008 5C LR S, A
0009 0A LR A, IS
000A 24C1 AI H'C1'
000C 94F9 BNZ A1
000E 71 LIS 1 SET SEC. FLAG
000F 53 LR SEC, A
0010 54 LR DL1, A SET DELAYS 1 AND 2
0011 55 LR DL2, A
0012 56 LR S1, A SET S1 AND S2
0013 2066 LI H'66'
0015 57 LR S2, A
0016 2041 LI H'41' SET INTERRUPT ADDRESS
0018 BC OUTS PC
0019 20A0 LI H'A0'
001B BD OUTS PD
001C 70 LIS 0
001D BE OUTS PE
001E 1B EI
0020 72 B0 LIS 2 GET CTRL
0021 B0 OUTS P0
0022 2B NOP
0023 A1 INS P1
0024 18 COM
0025 50 LR P, A
0026 70 CLR
0027 B0 OUTS P0
0028 A0 INS P0
0029 13 SL 1
002A 9171 BM C0 -, CLOCK SET
002C 63 LISU CT1
002D 13 SL 1
002E 8107 BP B1 +, COUNT-OFF
0030 41 LR A, FL ENABLE COUNTER
0031 2202 OI 2
0033 51 LR FL, A
0034 906B BR D0
0036 72 B1 LIS DISABLE COUNTER
0037 F1 NS FL
0038 51 LR FL, A
0039 6F LISL F
003A 70 CLR
003B E0 XS P
003C 9120 BM B4 -, RESET
003E 73 LIS 3
003F F0 NS P
0040 8418 BZ B3 0, SLOW/FAST NOT SET
0042 34 DS DL1
0043 945C BNZ D0 -0, DELAY 1 NOT OVER
0045 2080 LI H'80' RESET DELAY 1
0047 54 LR DL 1, A
0048 35 DS DL2
0049 9456 BNZ D0 -0, DELAY 2 NOT OVER
004B 71 LIS 1 RESET DELAY 2
004C F0 NS P
004D 71 LIS 1
004E 9402 BNZ B2 -0, FAST
0050 74 LIS 4 SLOW
0051 55 B2 LR DL2, A
0052 41 LR A, FL SET F/S FLAG
0053 2201 OI 1
0055 51 LR FL, A
0056 29016C JMP F1
0059 78 B3 LIS 8
005A F0 NS P
005B 8444 BZ D0 0, LOAD NOT SET
005D 40 B4 LR A, P SET BAUD RATE
005E 12 SR 1
005F 15 SL 4
0060 47 LR A, S2
0061 9103 BM B5 -, BAUD OF 110
0063 73 LIS 3 BAUD OF 50
0064 15 SL 4
0065 58 B5 LR BD, A
0066 15 SL 4 RESET DISPLAY
0067 5E LR D, A
0068 48 LR A, BD
0069 14 SR 4
006A 5E LR D, A
006B 70 CLR
006C 5C LR S, A
006D 6F LISL F SET BAUD RATE DISPLAY
006E 48 LR A, BD
006F 15 SL 4
0070 75 LIS 5
0071 9402 BNZ B6
0073 74 LIS 4
0074 18 B6 COM
0075 64 LISU CT2
0076 5E LR D, A
0077 63 LISU CT1
0078 15 SL 4
0079 EC XS S
007A 5D LR I, A
007B 78 LIS 8
007C F0 NS P
007D 8422 BZ D0 0, LOAD NOT SET
007F 74 LIS 4 GET LOAD NUMBER
0080 B0 OUTS P0
0081 2B NOP
0082 A1 INS P1
0083 18 COM
0084 840F BZ B8 0, LOAD NUMBER ZERO
0086 5A LR HU, A
0087 18 COM
0088 1F INC
0089 CC AS S
008A 8203 BC B7
008C 6E LISL E
008D 3D DS I
008E 4A B7 LR A, HU
008F 18 COM
0090 DC ASD S
0091 C7 AS S2
0092 D6 ASD S1
0093 5C LR S, A
0094 70 B8 CLR
0095 B0 OUTS P0
0096 9009
B9 BR D0
0098
009C 9043 BR C0
00A0 74 D0 LIS 4
00A1 F0 NS P
00A2 842A BZ D4 0, COUNT 2 SET
00A4 6F LISL F
00A5 4E LR A, D
00A6 12 SR 1
00A7 5B LR HL, A
00A8 7F LIS H'OF'
00A9 FC NS S
00AA 12 SR 1
00AB 5A LR HH, A
00AC 71 LIS 1
00AD FE NS D
00AE 8405 BZ D1
00B0 4B LR A, HL
00B1 2280 OI H'80'
00B3 5B LR HL, A
00B4 48 D1 LR A, BD SET DATA COUNTER ADDRESS
00B5 15 SL 4
00B6 4A LR A, HU
00B7 8403 BZ D2
00B9 2402 AI H'02'
00BB 2442
D2 AI H'42'
00BD 5A LR HU, A
00BE 10 LR DC, A
00BF 4C LR A, S
00C0 64 LISU CT
00C1 5D LR I, A
00C2 16 LM
00C3 25FF CI H'FF'
00C5 9406 BNZ D3
00C7 70 CLR
00C8 5E LR A, D
00C9 71 LIS 1
00CA C7 AS S2
00CB DC ASD S
00CC 5C D3 LR S, A
00CD 9062
D4 BR E0
00CF
00E0 62 C0 LISU CK
00E1 13 SL 1
00E2 13 SL 1
00E3 8105 BP C1 +, STOP CLOCK
00E5 71 LIS 1 ENABLE CLOCK
00E6 BE OUTS PE
00E7 9048 BR E0
00E9 70 C1 CLR DISABLE CLOCK
00EA BE OUTS PE
00EB 203C LI H' RESET SEC
00ED 53 LR SEC, A
00EE 6F LISL F
00EF 40 LR A, P
00F0 13 SL 1
00F1 8107 BP C2 +, RESET NOT SET
00F3 70 CLR RESET CLOCK DISPLAY
00F4 5E LR D, A
00F5 5E LR D, A
00F6 5C LR S, A
00F7 9038 BR E0
00F9 73 C2 LIS 3
00FA F0 NS P
00FB 8434 BZ E0 0, SLOW/FAST NOT SET
00FD 34 DS DL1
00FE 9431 BNZ E0 -0, DELAY NOT OVER
0100 71 LIS 1 RESET DELAY 2
0101 F0 NS P
0102 71 LIS 1
0103 9403 BNZ C3 -0, FAST
0105 20FF LI H'FF' SLOW
0107 54 C3 LR DL2, A
0108 0A LR A, IS
0109 07 LR QV, A
010A 1A DI
010B 09 LR P, A
010C 290130 JMP E0
1008 71 LIS 1
1009 C7 AS S2
100A DC ASD S
100B 2560 CI H'60'
100D 9414 BNZ C4
100F 70 CLR
1010 5E LR D, S
1011 71 LIS 1
1012 C7 AS S2
1013 DC ASD S
1014 2560 CI H'60'
1016 940B BNZ C4
1018 70 CLR
1019 5E LR D, S
101A 71 LIS 1
101B C7 AS S2
101C DC ASD S
101D 2513 CI H'13'
101F 9402 BNZ C4
1021 71 LIS 1
1022 5C C4 LR S, A
1023 900C BR E0
1030 42 E0 LR A, DR SET ISAR
1031 12 SR 1
1032 9404 BNZ E1
1034 6F LISL F
1035 9008 BR E3
1037 12 E1 SR 1
1038 9404 BNZ E2
103A 6E LISL E
103B 9002 BR E3
103D 6D E2 LISL D
103E 71 E3 LIS 1
103F F2 NS DR
1040 4C LR A, S
1041 8402 BZ E4 0, RIGHT CHAR
1043 14 SR 4 LEFT CHAR
1044 15 E4 SL 4 OUTPUT NUMBER
1045 E2 XS DR
1046 B1 OUTS P1
1047 71 LIS 1 ENABLE LATCH
1048 B0 OUTS P0
1049 70 CLR
104A B0 OUTS P0
104B B1 OUTS P1
104C EI (nop)
104D 32 DS DR DECR DISPLAY ROW FLAG
104E 8112 BP F0
1050 75 LIS 5 RESET DISPLAY ROW FLAG
1051 52 LR DS, A
1052 900E BR F0
1060 A0 F0 INS P0
1061 8134 BP F4 +, NO RDR SIGNAL
1063 78 LIS 8 CLEAR RDR LATCH
1064 B0 OUTS P0
1065 70 CLR
1066 B0 OUTS P0
1067 72 LIS 2
1068 F1 NS FL
1069 842C BZ F4 0, COUNT DISABLED
106B 63 LISU CT1
106C 6F F1 LISL F
106D 71 LIS 1
106E 18 COM
106F DC ASD S
1070 C7 AS S2
1071 D6 ASD S1
1072 5E LR D, A
1073 2599 CI H'99'
1075 9404 BNZ F2
1077 3C DS S
1078 9014 BR F3
107A 2500
F2 CI H'00'
107C 9410 BNZ F3
107E 7F LIS H'0F'
107F FD NS I
1080 940C BNZ F3
1082 48 LR A, BD
1083 15 SL 4
1084 5E LR D, A
1085 48 LR A, BD
1086 14 SR 4
1087 EC XS C
1088 5E LR D, A
1089 71 LIS 1
108A C7 AS S2
108B DC ASD S
108C 5C LR S, A
108D 71 F3 LIS 1
108E F4 NS FL
108F 8406 BZ F4
1091 E1 XS FL
1092 51 LR FL, A
1093 2940A0 JMP D0
1096 294020
F4 JMP B0
10A0 1E I0 LR J, W
10A1 06 LR QV, A
10A2 33 DS SEC
10A3 9425 BNZ I4
10A5 203C LI H'3C'
10A7 53 LR SEC, A
10A8 0A LR A, IS
10A9 07 LR QL, A
10AA 62 LISU CK
10AB 6F I1 LISL F
10AC 71 LIS 1 SEC
10AD C7 AS S2
10AE DC ASD S
10AF 2560 CI H'60'
10B1 9414 BNZ I3
10B3 70 CLR MIN
10B4 5E LR D, A
10B5 71 LIS 1
10B6 C7 AS S2
10B7 DC ASD S
10B8 2560 CI H'60'
10BA 940B BNZ I3
10BC 70 CLR HR
10BD 5E LR D, A
10BE 71 LIS 1
10BF C7 AS S2
10C0 DC ASD S
10C1 2513 CI H'13'
10C3 9402 BNZ I3
10C5 71 LIS 1
10C6 5C I3 LR S, A
10C7 03 LR A, QL
10C8 0B LR IS, A
10C9 02 I4 LR A, QU
10CA ID LR W, J
10CB 1B EI
10CC 1C POP
__________________________________________________________________________
Referring now to FIGS. 6 and 7 which together comprise a flow chart representation of the program carried out by the present invention, it will be seen that when the power is applied to the invention by way of power supply 90 the first program step carried out by microcomputer 30 is to determine whether or not a key has been depressed at keyboard 50. If no key has been depressed the program branches to the display and read sub-routine at junction "DIS" in FIG. 7. In the display and read sub-routine, hereafter referred to as the DIS routine, the contents of the count, time, or clock registers are first displayed and the program then checks to determine whether a time flag or count flag has been set and whether a tape reader signal has been received before returning to the key depression test. If a time flag or count flag has been set and a tape reader signal has been received, the program increments the time/count register before returning to the key test step in the program.
If, during the key test, encoder 20 indicates to microcomputer 30 that a key has been depressed, the next step in the program is to determine whether the key that has been depressed is either the clock, time, or count keys that pertain to the three possible modes of operation as previously described. If one of these three mode keys has been depressed the program then determines whether or not the load flag has been set which setting will occur when the enter key has also been depressed. If the enter key has been depressed and, as a result, the load flag has been previously set, the program again branches to the DIS routine as previously described. On the other hand, if the load flag set test indicates that the enter key has not yet been depressed, the program then performs the step of determining which of the mode keys have been depressed, the clock, time, or count key and sets the appropriate flag corresponding to that mode key before the program branches to the DIS routine.
If the test to determine whether or not the last key depressed is the count, time, or clock key yields a negative result, path "A" is followed and the routine next performs a test to determine whether the clock flag has been set. If the clock flag has not been set this indicates that the mode in which the invention is about to operate will be either the time mode or count mode as previously described. Accordingly, the program proceeds along path "B" to determine which mode (time or count) is to be put into effect and what is the current status with respect to operating in either of those two modes. As shown at the top-most portion of FIG. 7 at path "B", this begins with a test to determine whether the key START has been depressed. If the START key has been depressed, the program proceeds along the path labeled "C" to determine whether or not the T/C-ON flag (time or count on flag) has been set. If the time or count flag has been set, the program then sets the time or count on flag and proceeds to the the DIS routine as described above. If the TC-ON flag has not been set, the program then determines whether or not the load flag has been set. If the load flag has not been set, the time or count on flag is set and the program performs the DIS routine. If the load flag has been set, the program determines whether the contents of the time or count register are legal. The contents of the time or count register are illegal if the time register contains 60 seconds or more or if the count register contains a number equal to or larger than the total number of characters in one whole minute of transmission for the transmission rate selected, namely, TELEX or TWX. If the contents of both registers are legal, the time or count on flag is set and the program proceeds to the DIS routine. If the register contents are illegal, the program proceeds to the set error flag operation before proceeding to the DIS routine whereby the error indicating LED ERR is illuminated to inform the user of the error status.
If during the START key set test (at the top of FIG. 7) it is determined that the START key has not been depressed, instead of following the path labeled "C", the program proceeds to determine whether the STOP key has been set. If the STOP key has been set the program clears the time or count on flag and proceeds to the DIS routine. If the STOP key has not been set the program determines whether or not the T/C-ON flag has been set. If the T/C-ON flag has been set, an error condition is indicated and the error flag is set. If, however, this flag has not been set, the program then determines whether the LOAD key has been depressed. If the LOAD key has been depressed, the program sets the load flag and returns to the DIS routine. If the LOAD key has not been depressed, the load flag is tested and the error flag is set if the load flag has not been previously set. However, if the load flag has been set indicating that the LOAD key was previously set, the program then determines which of the two keys, TWX or TELEX, has been depressed and sets the appropriate flag according to which one has been depressed before returning to the display and read sub-routine. If neither transmission rate key has been depressed, the key number selected is loaded into the T/C register before the program returns to the DIS routine.
Returning to the clock flag test (FIG. 6), if the clock flag has been set indicating that the user has selected the clock mode, the program determines whether the START key has been depressed. If it has, as indicated by path "D" in FIG. 6, the clock register contents are tested to determine whether they are legal, that is, whether the contents of the clock register represent a corresponding time. If they do not, the clock register contents are illegal and the error flag is set before the program returns to the DIS routine. However, if the contents of the clock register are legal, the clock-on flag is set before the program returns to the DIS routine. If the START key test indicates that the START key has not been depressed, the program then tests the status of the STOP key. If the STOP key has been depressed, the clock-on flag is cleared and the program returns to the DIS routine. If the STOP key has not been depressed, the program then tests the status of the clock-on flag. If this flag has been set an error condition exists and the error flag is set before the program returns to the DIS routine. However, if the clock-on flag has not been set, the program tests the LOAD key status. If the LOAD key has been depressed, the clock register is cleared and the program returns to the DIS routine. However, if the LOAD key has not been depressed, the program tests whether any of the numerical value keys has been set. If none of those keys has been set, an error exists, the error flag is set and the program returns to the DIS routine. However, if one of the numerical value keys has been set, the program loads the key number into the clock register before returning to the DIS routine.
As previously indicated in the discussion of FIG. 5, a 60 Hz. signal is derived from the AC power supply and input to the microcomputer for purposes of providing a time base for clock counting operation. This 60 Hz. signal is handled as an external interrupt in the program as indicated in the lower right-hand portion of FIG. 6. As shown therein, the 60 Hz. signal generates a clock interrupt signal which results in the program decrementing the seconds count register. After this register is decremented it is tested to determine whether or not the count has reached zero. If it has not reached zero, the interrupt sequence is exited and the program returns to the step in the primary routine in progress when the interrupt was received. However, if the count has reached zero indicating that the 60th pulse in a 60 cycle signal has been received, which is equivalent to the time passage of one full second, the count register is reset and the clock register is incremented to reflect the passage of one second of time. After the clock register is incremented, the register contents are tested to determine whether the time indicated therein exceeds twelve hours, fifty nine minutes and fifty nine seconds. If this time is exceeded, the clock register is reset to zero, otherwise the clock sub-routine is exited.
From the above description of the structure of the invention and of the program contained within microcomputer 30, it will now be clear that the operation of the invention may be carried out as follows:
After the primary power is applied to the apparatus by connecting power supply 90 to a suitable AC source, the user selects which one of the three possible modes of operation is to be utilized.
When the invention is first activated, microcomputer 30 automatically selects the clock mode of operation and initiates a display of 00:00:00 and then continues to increment the display in one second intervals. The clock light CLK of LED array 60 is also illuminated to indicate the status of the program. The user may then select a different time to be displayed by depressing the STOP key on keyboard 50 and by then depressing appropriate numerical value keys for the selected time. As these keys are depressed, display 40 simultaneously displays the changes being made. After the start time is selected, the clock cycle is started by depressing the START key on keyboard 50 after which microcomputer 30 calculates the real time by using the 60 Hz. signal time base input from the line signal. If an illegal time has been entered, by way of example, 15 hours, 79 minutes and 83 seconds, microcomputer 30 recognizes the illegality of this entry and terminates changes in display 40 while illuminating error light ERR in LED array 60. In order to correct the illegal entry, the STOP key must be depressed and a legal time number entered by means of the numerical keys. On the other hand, if display 40 is to be started from zero time, only the ENTER key need be depressed and microcomputer 30 will automatically detect that condition and upon that entry will reset the time to 00:00:00 after the STOP key has been depressed and while it awaits depression of the next start command. Microcomputer 30 continues to track the real time which continues to run internally even if the time or count mode is selected. To recall real time it is only necessary to depress the CLOCK key on keyboard 50 for display 40 to revert to a real time display.
To activate the count mode, the user depresses the CNT key on keyboard 50 and then depresses the STOP key which results in constant information being displayed by display 40, and illumination of the LED count light CNT. The remaining sequences and operations of the count mode are similar to the below described sequences and operations of the time mode, except that display 40 displays the elapsed minutes and number of characters remaining before the next whole minute of message time is reached. Keyboard entry is also slightly different in that the user can pre-program the number of characters and time corresponding to sign-on and sign-off periods if he so desires. In both the time mode and count mode, after the LOAD key is depressed, the user can pre-program the approximate sign-on and sign-off times before selecting either the TELEX or TWX transmission rates.
If the time mode is desired, the time key on keyboard 50 is depressed resulting in the transfer of the corresponding key code by encoder 20 to microcomputer 30. Then the STOP key is depressed on keyboard 50 so that any information displayed in display 40 is stopped and at the same time LED, TIM, of array 60 is activated to indicate that the unit is in a time mode. The ENTER key is then depressed. This results in a status check by the microcomputer of the last number previously stored in scratch pad memory at the location corresponding to the displayed time. Such number is recalled from memory and again displayed. If zeros were previously stored in that location, the display indicated when the STOP key is depressed will remain unchanged. The user then depresses either the TELEX or TWX key on keyboard 50, depending upon the type of service being utilized. A new elapsed time can then be entered by the user by depressing appropriate keys of the numerical keys 0 through 9 on keyboard 50. Then the START key is depressed to enable microcomputer 30 to begin calculating the message time in minutes and tenths of minutes based upon the number of pulses received from the signal conditioner 80 input from tape reader 70. If the preset, elapsed running time is invalid, the error light ERR on the LED display 60 is illuminated and the display freezes. The user can then reset the error light and re-enter appropriate time data by first entering a legal time into the system by means of keyboard 50 and by then again depressing the START key.
SUMMARY
It will now be understood that what has been disclosed herein is a tape perforation feed-back device which calculates and displays the transmission time that will be required to send a message while it is being prepared for later transmission by teletypewriter exchange services such as TELEX, TWX, and the like. As a result of the present invention, users of teletypewriters exchange services can prepare their messages while anticipating the actual transmission charges. One important advantage resulting from such anticipation is that users can more efficiently utilize charge transmission time that would otherwise not be utilized for actual transmission of message information because of a whole minute round-up charge procedure. Thus the present invention provides a device for displaying data related to the message time required for the transmission of teletypewriter exchange service information which is compatible with both TELEX and TWX paper tape code language formats and with both TELEX and TWX message data rates and provides a portable low-cost message preparation timing system that does not require modification to the teletypewriter console per se.
Although a particular embodiment for carrying out the best mode of operation contemplated by the applicant has been disclosed herein, in which particular components of structural and programmable characteristics have been described, it will now be apparent to those having skill in the relevant art and with the benefit of applicant's teaching herein disclosed that many modifications may be made to the present invention. By way of example, other ways of coupling the invention to a teletypewriter console may be contemplated as well as additional modes of operation, keys, and display features which are modifications of the preferred embodiment disclosed. However, all such modifications are contemplated to be within the scope of the present invention which is to be limited only by the appended claims.
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- Inventors
Weiss, Gary A.;
- Assignee
Pacesetter Management Corp. (Los Angeles, CA)
- Published
Aug-25-1981
- Current US Classes:
178/17B
178/23R
346/94
377/20
377/26
705/418
- Application #
148107
- International Classes
G07C 001/10; H04L 015/24; H04M 015/18
- Field of Search
178/23 179/6.31 179/7.1 364/467 235/92 346/94 400/62 400/78
- Examiner
Robinson; Thomas A.
- Agent
Fischer and Tachner
- US Patent References:
4041291
4065663
4195220
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