Remote control security system

Abstract

A remote control keyless security system for remotely controlling the locking and unlocking control functions of a lock mounted on a vehicle or the like. A receiver is mounted on a vehicle proximate to the lock to be controlled. A transmitter is located remote from the receiver and includes a plurality of selectively actuatable switches each representative of a control function to be performed by the lock and circuitry responsive to actuation of one of the switches for transmitting a digital signal including a first portion having a multi-bit security code uniquely identifying the transmitter from that of a plurality of similar transmitters, a multi-bit sequence control code adapted to be sequentially changed in response to each actuation of a switch and a multi-bit function code identifying one of a plurality of control functions to be performed by the lock. The transmitter changes the sequence control code after each operation with the change being dependent upon information contained in the security code identifying the transmitter. The receiver stores a multi-bit receiver security code identifying a specific transmitter from which the receiver may validly receive a digital signal. The received security code is compared with the stored receiver security code to determine whether the security codes match. The receiver also stores a multi-bit sequence control code.

Claims

Having described the invention, the following is claimed:

1. A method of operating a portable transmitter to remotely control at least one function on a vehicle in a secure manner, comprising the steps of:

providing a manually operable switch on said transmitter for use in manually signalling that a function on the vehicle is to be operated;

generating a message for transmission to the vehicle for controlling a function on the vehicle in response to operation of the manually operable switch;

generating an error detecting code based upon said message for use in detecting errors in transmission of said message;

scrambling said message in dependence upon the generated error detecting code and one of a fixed plurality of scrambling algorithms and wherein said error detecting code is generated for a primary purpose unrelated to any of said scrambling algorithms but wherein a secondary purpose is to describe said one of a fixed plurality of scrambling algorithms for selection in accordance with said error detecting code; and

transmitting the scrambled message and the unscrambled error detecting code to said vehicle.

2. A portable transmitter for remotely controlling at least one function on a vehicle in a secure manner, comprising:

a small, hollow transmitter housing adapted for easy transportation in a person's pocket;

a manually operable switch mounted in said housing and manually operable from the outside of said housing to control operation of the function;

electronic means contained within said housing and responsive to said switch for (a) generating a message for transmission to the vehicle for controlling a function on the vehicle, (b) generating an error detecting code based upon said message for use in detecting errors in transmission of said message, (c) scrambling said message in dependence upon the generated error detecting code and one of a fixed plurality of scrambling algorithms and wherein said error detecting code is generated for a primary purpose unrelated to any of said scrambling algorithms but wherein a secondary purpose is to describe said one of a fixed plurality of scrambling algorithms for selection in accordance with said error detecting code and (d) transmitting the scrambled message and the unscrambled error detecting code to said vehicle; and

portable power source means contained within said housing for powering said electronic means.

3. A portable transmitter for remotely controlling at least one function on a vehicle in a secure manner, comprising:

a small, hollow transmitter housing adapted for easy transportation in a person's pocket;

a manually operable switch mounted in said housing and manually operable from the outside of said housing to control operation of the function;

electronic means contained within said housing and responsive to said switch for (a) generating a message for transmission to said vehicle, said message containing a control code indicative of the desired operation and a security code uniquely identifying said transmitter, (b) generating an error detecting code based upon said message for use in detecting errors in transmission of said message, (c) scrambling said message in dependence upon the generated said error detecting code and one of a fixed plurality of scrambling algorithms and wherein said error detecting code is generated for a primary purpose unrelated to any of said scrambling algorithms but wherein a secondary purpose is to describe said one of a fixed plurality of scrambling algorithms for selection in accordance with said error detecting code, and (d) transmitting the scrambled message and the unscrambled error detecting code to said vehicle; and

portable power source means contained within said housing for powering said electronic means.

Description

FIELD OF THE INVENTION

The present invention relates to the art of remote control of security systems and, more particularly, to controlling the locking and unlocking functions of a lock, such as on a motor vehicle's door or trunk lid or the like.

DESCRIPTION OF THE PRIOR ART

Remote control security systems are known in the art for controlling the locking and unlocking functions of a lock mounted on a motor vehicle and such systems typically comprise a receiver mounted on the vehicle proximate to the lock to be controlled and a portable handheld transmitter located remote from the receiver. A system such as that described above is disclosed in my U.S. Pat. No. 4,881,148, the disclosure of which is incorporated herein by reference. That patent discloses a system wherein a receiver has a memory which stores one or more security codes, each of which identifies a transmitter from which the receiver will validly receive a transmitted signal. Each transmitter is provided with a plurality of actuatable switches, each representative of a control function to be performed by the lock, such as an unlock function, or a lock function, or an unlock a truck lid function. Also, each transmitter includes circuitry that responds to the actuation of one of the switches to transmit a digital signal which includes a security code which uniquely identifies the transmitter from that of a plurality of similar transmitters, along with a function code representative of the particular control function to be performed by the lock. When a receiver receives such a digital signal it compares the received security code with each stored security code to determine if a match exists indicative that the receiver may validly receive the digital signal and respond thereto. If a match takes place, then the receiver responds to the function code for performing the control function requested, such as lock or unlock a vehicle door.

A concern with respect to such a system is that a would-be thief desiring entry into a locked vehicle may record the transmitted digital signal with appropriate radio frequency receiving equipment. Such recorded information may then be employed by such a thief for purposes of gaining access into such a locked vehicle.

In an effort to thwart the activities of a thief, systems have been devised which change the security code of the transmitter each time such a digital signal is transmitted and a corresponding change is made to the security code stored at the receiver. Thus, both the transmitter and the receiver may be provided with code generators which generate a succession of differently coded signals such that the security code is updated in the same manner at both the transmitter and the receiver after each operation. A system of this type is disclosed in the Bongard et al. U.S. Pat. No. 4,596,985.

The prior art noted above requires that the security code, sometimes referred to as access code or identity code, be changed after each operation. This may present a difficulty in that by making changes to the security code, then the security code transmitted by a transmitter may inadvertently be changed to a code that permits unwanted access to a receiver having the same security code.

The prior art noted above does not provide that the security code remain fixed and that the transmitted digital signal include an additional code which changes after each transmission such that the change is dependent upon information contained in the security code. Moreover, there is no teaching in the prior art that the additional code, sometimes referred to herein as a sequence control code, be received at the receiver for comparison with a similar sequence control code and which, after each operation, is updated by changing its digital value dependent upon information contained in the security code stored at the receiver.

In addition to the foregoing, the prior art noted above does not provide a teaching wherein the transmitted codes are scrambled or that the order of transmission of the codes be varied.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, apparatus and method are provided whereby a transmitter remotely controls the locking and unlocking functions of a lock mounted on a vehicle or the like wherein the transmitter includes a plurality of selectively actuatable switches each representative of a function to be performed by the lock, such as lock or unlock a vehicle door or unlock a trunk lid. In response to actuation of one of the switches, a digital signal is transmitted by the transmitter with the digital signal including a first portion having a multi-bit security code uniquely identifying the transmitter from that of similar transmitters, a multi-bit sequence control code that is sequentially changed in response to each actuation of one of the switches and a multi-bit function code identifying one of a plurality of the control functions to be performed by the lock. The transmitter responds to each actuation of one of the switches for sequentially changing the digital value of the sequence control code with each change being dependent upon information contained in the security code that identifies the transmitter.

In accordance with another aspect of the present invention, a receiver is provided for use in receiving a digital signal as described above and wherein the receiver includes a memory that stores a multi-bit receiver security code which identifies a specific transmitter from which the receiver may validly receive a transmitted digital signal together with circuitry for comparing the received security code with the stored security code to determine if the codes match. A multi-bit sequence control code is also stored in memory in the receiver and circuitry is provided which responds to each occurrence of a match between the security codes for reading the stored sequence control code and changing its digital value to define an updated sequence control code having a digital value dependent upon information contained in the stored receiver security code. The updated sequence control code and the stored sequence control word are compared to determine whether a match exists and, if so, the lock is controlled to perform the function defined by the received function control code.

Still further in accordance with the present invention, a remote control security system is provided including a receiver as described hereinabove along with at least one transmitter as described hereinabove.

Still further in accordance with another aspect of the present invention, the transmitted digital signal includes a second portion having a multi-bit second code and wherein the codes in the first portion of the transmitted digital signal are scrambled in accordance with one of a plurality of scrambling algorithms and wherein the second code in the second portion of the transmitted digital signal includes information as to which one of the plurality of scrambling algorithms is employed.

Still further in accordance with another aspect of the present invention, the receiver de-scrambles the codes in the first portion of the received digital signal in dependence upon information contained in the received second code.

Still further in accordance with another aspect of the present invention, the codes in the first portion of the transmitted digital signal are arranged in order for transmission in accordance with one of a plurality of transmission order algorithms and that the second code includes information as to which one of the transmission order algorithms was employed for arranging the order of the codes.

Still further in accordance with another aspect of the present invention, the receiver rearranges the order of the codes in the first portion of the received digital signal based upon information contained in the received second code.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects of the invention will become more readily apparent from the following description of the preferred embodiment of the invention as taken in conjunction with the accompanying drawings which are a part hereof and wherein:

FIG. 1 is a schematic block diagram including FIGS. 1A and 1B respectively illustrating a transmitting unit and a receiving unit of a remote control security system employing the present invention;

FIG. 1C is a perspective pictorial view of the transmitting unit in the form of a keyholder;

FIG. 2 is an illustration of voltage with respect to time illustrating the waveform of a transmitted digital signal provided by the transmitting unit herein and which illustration is useful in describing the invention herein;

FIG. 3 is a flow diagram illustrating the operation of the programmed microcomputer employed in the transmitter of FIG. 1; and

FIG. 4 is the flow diagram including FIGS. 4A and 4B together illustrating the programmed operation of the microcomputer employed in the receiver of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT

Reference is now made to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting same. FIG. 1 shows a remote control A for selectively operating a door lock mechanism B, door unlock mechanism C or trunk solenoid D to release the trunk of a motor vehicle. System A includes a transmitting unit T for creating a coded digital signal S to be transmitted to receiver unit R, whereby the doors of the vehicle can be locked or unlocked or the trunk can be released at will from a distance of at least 20-50 feet. Transmitting unit T includes a microcomputer having appropriate internal PROMs, EEPROMs and RAMs programmed to perform the functions of the system, as hereinafter described, and having sufficient I/O terminals controlled by selector means or switches 12, 14, and 16. In accordance with the illustrated embodiment, switch 12 is depressed when system A is to lock the doors of the vehicle by operating door lock mechanism B. In a like manner, switch 14 is manually operated to unlock the vehicle doors by actuating door unlock mechanism C. The trunk solenoid D or mechanism for unlatching the vehicle trunk lock is actuated by depressing manual switch 16. Upon depressing one of these switches 12-16, a power up circuit 20 is actuated to direct power to the microcomputer 10 and actuate oscillators 30 and 32. In the preferred embodiment switches 12, 14, and 16 power system A and cause a single transmission of a coded signal. Thereafter, circuit 20 is deactivated to await a new requested function.

Oscillator 30 has a nominal frequency of 315 MHz, in the preferred embodiment, which frequency is essentially the same frequency employed for common garage door operators. Whereas the invention is described herein with reference to an RF system, it may also be practiced with an IR system. Clock oscillator 32 is unregulated in that it does not have a crystal control and may vary as to its frequency with temperature changes and manufacturing tolerances. The output of oscillator 32 is used to time the function of microcomputer 10 to shift output line 38 to a logic 1 whenever a binary 1 is to be transmitted by antenna 36. Microcomputer output line 38 is one input of AND gate 39 having a second input controlled by the output of oscillator 30. The signal in output line 37 of gate 39 is a series of binary conditions (logic 0 and logic 1) superimposed on a 315 MHz carrier. Consequently, transmitted signal S, when microcomputer 10 is powered by circuit 20, will be a series of pulses having a length or duration controlled by the logic in line 38. Lines P are power lines actuated upon command of circuit 20.

As will be described later, the code in signal S is binary, with a binary 1 and a binary 0 being distinguished from each other by having a difference in length or duration. This pulse length is controlled by the frequency of oscillator 32 which is not a high priced oscillator with quartz control; therefore, the relationship between a binary 0 and a binary 1 for the identification code in transmitted signal S is the relative pulse lengths of a logic 1 and a logic 0. These lengths vary according to the particular frequency of oscillator 32 but maintain their numerical relationship since they are based upon counts of the clock in line 34. In this manner, oscillator 32 can be relatively inexpensive but the frequency or clock in line 34 will not be identical from one transmitter T to another transmitter. Indeed, during different operating conditions in a particular transmitting unit the clock in line 34 can drift in frequency.

By employing the power up concept, power at lines P is not applied to the oscillators and the microprocessor until there is a selection by depressing one of the switches 12-16. When this occurs, power up circuit 20, which includes a battery (normal 5.0 volts), directs power to the microcomputer for a time which is controlled by the microcomputer. The length of the time the microcomputer maintains power is sufficient to transmit one control signal. This signal includes, in practice, a wake up signal, at least one initiation bit, thirty-two bits of security code, twenty-four bits of sequence control code, eight bits of checksum code and eight bits of function code to indicate which switch 12-16 has been closed.

As illustrated in FIG. 1C, transmitting unit T is a handheld key ring having an appropriate array of finger tip switches 12-16, in a case 50 which can include a key ring 52 on a swivel connection 54. Transmitter case 50 is a small hollow housing containing the transmitter circuitry and a power source, such as a battery. The case is adapted for easy transportation in a person's pocket. The handheld case 50 is retained by the operator of the vehicle so that as the operator approaches the vehicle, signal S can be transmitted to receiver R by merely depressing one of the finger operated switches 12-16 mounted in the case 50 and manually operable from outside of the case.

The microcomputer 10 of the transmitter is provided with internal memories including PROMs, EEPROMs and RAMs. As is well known, such memories include registers for storing multi-bit codes. Whereas these registers are internal of the microcomputer 10, four of these registers are illustrated in FIG. 1 to assist in the explanation of the invention. These registers include a security code register 40, a sequence control code register 42, a function code control register 44 and a checksum code register 46. Registers 40 and 42 are in the EEPROM memory whereas registers 44 and 46 are in RAM. The security code register 40 contains a fixed code which uniquely identifies the transmitter T from that of other similar transmitters. The register contains a security code which is fixed in the transmitter by the manufacturer and may be implemented in a manner described hereinbefore with my previous U.S. Pat. No. 4,881,148. The security code preferably takes the form of four eight bit bytes.

Another register 42 is referred to herein as the sequence control code register and it stores a sequence control code which is preferably twenty-four bits long divided into three eight bit bytes. As will be brought hereinafter, the digital value of the sequence control code is changed each time one of the switches 12, 14 or 16 is actuated and, hence, this is a sequentially changing code. This code is changed in accordance with one of a plurality of sequence control algorithms stored in a look-up table in the transmitter microcomputer 10. Also, as will be brought out in greater detail hereinafter, the determination as to which one of the plurality of sequence control algorithms to be employed is determined by examining information contained in the security code stored in register 40.

A function code register 44 serves to temporarily store the function code to be transmitted as part of a transmitted digital signal S. This preferably takes the form of an eight bit coded byte with the bits being arranged in response to actuation of one of the switches 12, 14, 16 so that the function represented thereby is to either lock the vehicle door, unlock the vehicle door or unlock the trunk lid by actuating the trunk solenoid.

Another register in the microcomputer 10 is a checksum code register 46. This register contains an error detecting code known as a checksum code. This code is placed into the register by the microcomputer under program control in a known manner. For example, the data to be transmitted is examined and an eight bit checksum code is placed into the register for use in verifying the accuracy of the transmitted signal.

The transmitted digital signal S is illustrated in FIG. 2 and it includes a wake up portion 11 and which may comprise a single bit, but which is of an elongated duration such as on the order of twelve milliseconds and this is followed by a start or initiation portion 13 and which may comprise four bits. The checksum code 15 includes 8 bits and the security code 17 contains 32 bits. The sequence control code 19 contains 24 bits and the function code 21 contains eight bits. As will be brought out in greater detail hereinafter, the digital signal is transmitted in the order of the wake up code 11, followed by the initiation code 13. This is followed by an eight bit checksum code, four eight bit bytes of security code, three eight bit bytes of sequence code and an eight bit function code. The checksum code in this embodiment of the invention will always be in the same place. For example, this code may be the first byte of the nine bytes which follow the transmission of the initiation bits. The remaining eight bytes may be varied in sequence and/or scrambled as will be discussed hereinafter. Moreover, the digital value of the sequence control code is changed with each transmission of a digital signal.

The receiver R includes an RF detector 60 tuned to the transmitted frequency of 315 MHz so that, as the digital signal S is received at the receiver's antenna 61, the detector recognizes the frequency of the signal and allows the first portion including the wake up portion 11 to pass to a wake up signal detector 62. The detector 62 checks to see if the wake up condition is proper and, if so, it activates the wake up circuit 64. Circuit 64 acts as a power up circuit for supplying operating voltage, such as 5 volts, to the receiver's microcomputer 80. The operating voltage is monitored by a low voltage detector 68 to permit operation of the circuitry so long as the voltage does not drop below a selected level.

The data in the received digital signal S is supplied to the microcomputer 80 and is clocked in by clock pulses obtained from a clock oscillator 82. The microcomputer 80, as in the case of the microcomputer 10, includes a plurality of internal memories including PROMs, RAMs and EEPROMs. The internal memories are programmed to perform the functions to be described in greater detail hereinafter.

Some of the internal memories of the microcomputer 80 are illustrated in FIG. 1 to assist in the description of the invention herein. These include registers 100, 102, 104 and 106 which are all in the non-volatile memory (EEPROM). Register 100 stores a security code A that uniquely identifies a transmitter from which the receiver may validly receive a digital signal. The code set into register 100 may be placed in the memory at the factory or may be programmed in the field in the manner as described in my previous U.S. Pat. No. 4,881,148. The security code is generated by means of an algorithm which has the capability of generating numbers in a random, but not repeatable, fashion. This code is thirty-two bits in length and is divided into four eight bit data bytes. As it may be desirable for the receiver to validly receive digital signals from more than one transmitter, a second security code register 104 is provided, identical to that of register 100, but which includes a security code B which is uniquely different from that of security code A in register 100.

In addition to register 100, the receiver includes a companion register 102 which has been programmed to contain a multi-bit sequence control code. As discussed herein with respect to the transmitter, this code is a twenty-four bit code divided into three eight bit bytes. This code is varied by a predetermined amount, known only to the manufacturer, each time the receiver has determined that it has received a valid digital signal, as will be described in detail hereinafter. Since it may be desirable to validly receive a digital signal from a second transmitter, a second sequence control code is stored in a second register 106 and in a like manner this sequence control code is changed each time the receiver has determined that it has validly received a digital signal from the second transmitter (or B transmitter)

Also, to assist in describing the invention herein, there is shown in FIG. 1 a pair of registers located in internal memory of the microprocessor 80 and these include a function code register 108 and a checksum code register 110. These are temporary memories and respectively serve to receive and store the function code and checksum code portions of the digital signal S received from the transmitter T.

As will be described hereinbelow, if the receiver validly receives a digital signal from a transmitter, it will then decode the function code in register 108 and perform one of the door lock control functions such as locking a vehicle door or unlocking a vehicle door or actuating a trunk solenoid by way of suitable load drivers 120 controlled by the microcomputer 80.

Reference is now made to FIG. 3 which illustrates the flow chart showing the manner in which the microcomputer in the transmitter is programmed in accordance with the present invention. Initially, the transmitter is at rest in a standby condition sometimes known as a power-down condition, and this is indicated as step 200 in FIG. 3. The microcomputer is now awaiting closure of one of the switches 12, 14 or 16.

In step 202, the microcomputer responds to the closure of one of the switches 12, 14 or 16 and initially actuates the power up circuit 20 in accordance with step 204 for purposes of applying power on lines P to the various circuits within the transmitter.

In step 206, the microcomputer is programmed to read the actuated switch to determine which switch 12, 14 or 16 was actuated and then store the function code associated with that switch in the function code register 44 in accordance with step 208. The function code stored in the register 44 now represents the specific request, such as lock the vehicle door or unlock the vehicle door or unlock the trunk lid.

In step 210, the microcomputer reads the present or old sequence control code from the register 42 in order to update the sequence control code in accordance with step 212. The computer performs a read function at step 214 wherein the security code register is read to obtain the security code for this transmitter. Having obtained the security code from register 40, the computer now reads from a look-up table A, pursuant to step 216, to determine which one of a plurality of sequence control variation algorithms is to be employed in determining the new sequence control code in accordance with step 218. Once the correct algorithm has been obtained from Table A in accordance with step 216, the next or new sequence control code is determined to obtain an updated sequence control code in accordance with step 212. This new sequence control code is then stored in the sequence control register 42 pursuant to step 220.

Reference is now made to Table A produced below.

                  TABLE A
    ______________________________________
    SEQUENCE CONTROL CODE METHOD OF VARIATION
    Security Code: Axxxxxxx Bxxxxxxx Cxxxxxxx Dxxxxxxx
    ABCD
    ______________________________________
    0000          Increment by
                              1
    0001                      3
    0010                      5
    0011                      7
    0100                      9
    0101                      11
    0110                      13
    0111                      15
    1000          Decrement by
                              1
    1001                      3
    1010                      5
    1011                      7
    1100                      9
    1101                      11
    1110                      13
    1111                      15
    ______________________________________

                  TABLE B
    ______________________________________
    KEY TO SCRAMBLING METHOD
    CHECKSUM
    CODE       SCRAMBLING METHOD
    ______________________________________
    0000 xxxx   1. XOR with SCC-1 - Shift Left
                                  1 & Invert
    0001 xxxx   2. XOR with SCC-1 - Shift Left
                                  1
    0010 xxxx   3. XOR with SCC-1 - Shift Left
                                  2 & Invert
    0011 xxxx   4. XOR with SCC-1 - Shift Left
                                  2
    0100 xxxx   5. XOR with SCC-1 - Shift Left
                                  3 & Invert
    0101 xxxx   6. XOR with SCC-1 - Shift Left
                                  3
    0110 xxxx   7. XOR with SCC-1 - Shift Left
                                  4 & Invert
    0111 xxxx   8. XOR with SCC-1 - Shift Left
                                  4
    1000 xxxx   9. XOR with SCC-1 - Shift Right
                                  1 & Invert
    1001 xxxx  10. XOR with SCC-1 - Shift Right
                                  1
    1010 xxxx  11. XOR with SCC-1 - Shift Right
                                  2 & Invert
    1011 xxxx  12. XOR with SCC-1 - Shift Right
                                  2
    1100 xxxx  13. XOR with SCC-1 - Shift Right
                                  3 & Invert
    1101 xxxx  14. XOR with SCC-1 - Shift Right
                                  3
    1110 xxxx  15. XOR with SCC-1 - Shift Right
                                  4 & Invert
    1111 xxxx  16. XOR with SCC-1 - Shift Right
                                  4
    ______________________________________

                  TABLE C
    ______________________________________
    CHECKSUM CODE   KEY TO OUTPUT ORDER
    ______________________________________
    xxxx 0000       Output order   1
    xxxx 0001                      2
    xxxx 0010                      3
    xxxx 0011                      4
    xxxx 0100                      5
    xxxx 0101                      6
    xxxx 0110                      7
    xxxx 0111                      8
    xxxx 1000                      9
    xxxx 1001                     10
    xxxx 1010                     11
    xxxx 1011                     12
    xxxx 1100                     13
    xxxx 1101                     14
    xxxx 1110                     15
    xxxx 1111                     16
    ______________________________________

                  TABLE B'
    ______________________________________
    Key to De-scrambling Method
    Checksum
    Code     De-scrambling Method
    ______________________________________
    0000XXXX  1. Invert -
                       Shift Right
                                 1 - XOR with SCC-1
    0001XXXX  2.       Shift Right
                                 1 - XOR with SCC-1
    0010XXXX  3. Invert -
                       Shift Right
                                 2 - XOR with SCC-1
    0011XXXX  4.       Shift Right
                                 2 - XOR with SCC-1
    0100XXXX  5. Invert -
                       Shift Right
                                 3 - XOR with SCC-1
    0101XXXX  6.       Shift Right
                                 3 - XOR with SCC-1
    0110XXXX  7. Invert -
                       Shift Right
                                 4 - XOR with SCC-1
    0111XXXX  8.       Shift Right
                                 4 - XOR with SCC-1
    1000XXXX  9. Invert -
                       Shift Left
                                 1 - XOR with SCC-1
    1001XXXX 10.       Shift Left
                                 1 - XOR with SCC-1
    1010XXXX 11. Invert -
                       Shift Left
                                 2 - XOR with SCC-1
    1011XXXX 12.       Shift Left
                                 2 - XOR with SCC-1
    1100XXXX 13. Invert -
                       Shift Left
                                 3 - XOR with SCC-1
    1101XXXX 14.       Shift Left
                                 3 - XOR with SCC-1
    1110XXXX 15. Invert -
                       Shift Left
                                 4 - XOR with SCC-1
    1111XXXX 16.       Shift Left
                                 4 - XOR with SCC-1
    ______________________________________

• Inventors
  Lambropoulos, George P.;
• Assignee
  TRW Inc. (Lyndhurst, OH)
• Published
  Feb-18-1997
• Current US Classes:
  340/5.26
  340/5.64
  340/825.69
  380/262
  380/28
  380/37
  714/758
• Application #
  514398
• International Classes
  H04Q 001/00
• Field of Search
  340/825.3 340/825.31 340/825.32 340/825.69 340/825.72 380/21 380/28 380/36 380/37 380/49 380/43 380/23 371/37.7
• Examiner
  Zimmerman; Brian
• Agent
  Tarolli, Sundheim, Covell, Tummino & Szabo
• US Patent References:
  4596985
  4630272
  4743898
  4847614
  4864494
  4881148
  5055701
  5107258
  5146498
  5159329
  5182752
  5222137
  5249230
  5253296