Digital lock system having electronic key card

[57] ABSTRACT

An electronic lock system in which a coded data word is stored in a key and, upon insertion of the key into a lock, compared with a master code. A predetermined correspondence between the key code and the master code causes the provision of an output signal for actuation of the lock or other utilization apparatus. Lack of correspondence between the key code and master code will not cause production of the output signal and can be employed to cause actuation of an alarm indication. Digital circuitry is employed in both the key and lock and is configured to permit easy alteration of the stored code to greatly enhance system security.

Claims, 10 Drawing Figures

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PATENTED JAN 71975

3,859,634

SHEET 1 OF 4

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ENABLE CODE

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PATENTED JAN 71975

3,859.634

SHEET 2 OF 4

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PATENTED JAN 71975

3,859,634

SHEET 3 OF 4

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PATENTEDJAN 71975 3,859,634

SHEET U OF 4

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3,859,634

DIGITAL LOCK SYSTEM HAVING ELECTRONIC KEY CARD

RELATION TO OTHER APPLICATIONS

This application is a continuation-in-part of copending application Ser. No. 132,671, filed Apr. 9, 1971, now abandoned in favor of continuation application Ser. No. 273,529, filed July 20, 1972.

FIELD OF THE INVENTION

This invention relates to lock systems and more particularly to an electronic lock system employing active digital electronic circuitry in both the key and lock.

BACKGROUND OF THE INVENTION

Electronic locks have been proposed in which an electronic circuit in a lock is energized to activate the lock by use of a key containing circuitry cooperative with the lock circuit. The circuitry employed in a key has generally been of a type in which a plurality of coded interconnections is provided to appropriately energize an associated lock circuit. Such key circuitry, however, usually contains a fixed code which is alterable only be rewiring of the key circuit. There is little versatility of coding in such conventional systems. In addition, the configuration of the key circuit can be ascertained by appropriate analysis and the code thereby duplicated. As a further disadvantage, such keys usually require a relatively large number of interconnections with the lock, with attendant increase in system cost and complexity.

SUMMARY OF THE INVENTION

In accordance with the present invention, a highly reliable and secure electronic lock system is provided in which active data storage means are provided within a key containing a readily alterable coded data word corresponding to a master code stored in an associated lock circuit. Upon insertion of the key into the lock, the data stored in the key is compared with a master code in the lock, a predetermined correspondence therebetween causing actuation of the lock. In the event that there is not proper comparison between the master code and the key code, an alarm can be actuated and the key can also be seized within the lock to prevent its removal therefrom. By immediate actuation of an alarm in the event of detection of one or more incorrect bits of the key code, there is little opportunity to attempt duplication of the key code, thus materially enhancing system security. Analysis of the data storage circuitry within the key will not reveal the data code stored therein and even if the stored data were read out by interrogation of the key, the data can be selectively coded such that it would be, in practice, substantially impossible to analyze and decode the data content thereof.

In a typical embodiment of the invention, the key contains an electronic data memory such as a multiple bit shift register or read-only memory for storing the key code therein and is typically of integrated circuit type having extremely low energy requirements. Power can be provided by a small battery source located within the key. Alternatively, the data memory can be of the non-volatile type requiring no external power, in which case no battery need be employed. Data provided between the key and lock is preferably in serial form to minimize the number of interconnections re quired between the key and the associated lock. Various interconnection configurations are contemplated by the invention. Two data connections can be provided, one for transferring data from the key to the lock, and one for transferring data from the lock back into the key. Or, a single data line can be shared for bidirectional transmission. A clock line can be provided depending upon whether a self clocking data code is employed, and a ground connection is also usually employed. Connection between the key and lock can be made by various well known coupling means suited to particular system requirements, such as electrical contact elements, or inductive, photoelectric or other noncontacting coupling.

It will be appreciated that the invention is not limited to use in actuating a lock as such, but is generally useful in security systems wherein an output signal is applied to utilization apparatus only upon the requisite comparison between a master code and a key code. For example, the invention is useful to operate many different key actuated devices in addition to locks, such as electrical switches, identification apparatus and the like. Moreover, the key can contain other data in addition to the key code as may be desirable in particular instances. The key can, for example, also contain data representing the identity of the key holder, an account number or various other data to suit operational requirements. Such additional data can be employed as part of the decoding process to cause an output indication, or the additional data can be separately decoded for distinct purposes, as required.

DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a simplified block diagram representation of a lock system according to the invention;

FIG. 2 is a block diagram of an alternative key circuit embodying the invention;

FIG. 2A is a block diagram of a further key circuit embodying the invention;

FIG. 3 is a partial block diagram of an alternative lock circuit embodying the invention;

FIG. 4 is a block diagram of yet another lock circuit according to the invention;

FIG. 5 is a more detailed block diagram of a lock system according to the invention;

FIG. 6 is a block diagram of a self-clocking key circuit embodying the invention;

FIG. 7 is a partial schematic and partial block diagram of a key energizing technique according to the invention;

FIG. 8 is a pictorial view, partly in section, illustrating a typical key configuration embodying the invention; and

FIG. 9 is a block diagram of a photoelectric coupling technique useful in the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 there is shown an electronic key 10 having a memory 12 powered by a suitable energy source such as a battery 14. The memory is typically a shift register of the low power type constructed by monolithic integrated circuit techniques and is, therefore, of extremely small physical configuration capable of being readily mounted in a small key member. The

3,859,634 battery is typically a low power mercury battery also adapted for mounting in the key member and capable of energizing memory 12 for a long period of time. The power requirements of an integrated circuit shift register are sufficiently small that the effective life of battery 14 is determined more from the shelf life thereof rather than the power drain. The key 10 is cooperative with an electronic lock 16 and is coupled thereto by three lines, labeled data out, data in and clock. The data out line carries data from memory 12 to the lock circuit, the data in line carries data from the lock circuit back into memory 12, and the clock line carries clock pulses for shifting of data in and out of memory 12. In actual implementation, a ground line may also interconnect key 10 and lock 16.

The lock circuit 16 includes a data gate 18 connected to a memory 20, and operative to couple data from memory 12 to memory 20, and to recirculate data from memory 12 back into memory 12 for restorage of a key code therein. The memory 20 has an output thereof coupled to a comparator 22 which also receives data from a master code generator 24. The output of comparator 22 is connected to logic circuitry 26 which provides a first output signal for actuation of associated utilization means, and a second output signal for providing an alarm indication in the event that an improper key code is employed.

Memory 20 and associated components of the lock 16 can also be typically implemented by integrated circuits. Timing of data from the key to the lock circuit is accomplished by means of a clock 28 providing clock signals to memory 12 and to a control circuit 30 which governs operation of memory 20 and also provides master timing signals to the lock system. An insertion detector 32 is provided in the lock for sensing the presence of key 10 therein and for providing, in response to key detection, a start signal to clock 28 for initiation of the key identification process. As will be described, the insertion detector 32 can also cause mechanical clampling of the key within the lock to prevent its premature withdrawal during the code recognition cycle and also to capture the key in the event that an improper key code is detected.

In operation, a multiple bit data word specifying a key code is stored in memory 12 representative of a unique key identity, this code being identical to a master code provided by generator 24 located in the lock circuitry. The key code contained within memory 12 is compared with the master code, positive identity between the two codss enabling actuation of the lock. Noncorrespondence between one or more bits of the key code and the master code causes actuation of an alarm, indicating an attempt to utilize an improper key. Upon insertion of key 10 into lock 16, the presence of the key as determined by insertion detector 32 cuases enabling of clock 28. Clock pulses from clock 28 are applied to memory 12 and cause readout of the data stored therein to data gate 18 and thence to memory 20.

The data being shifted out of memory 12 is also recirculated via data gate 18 back into memory 12 to reload the key code for subsequent use. Upon loading of the data word into shift register 20, comparator 22 is operative to compare the data contents of register 20 with that of master code generator 24 and to provide output signals to logic 26 indicative of whether or not the coded data from key 10 corresponds to the master code pattern. Comparison of the key code with the master code can be accomplished on a bit by bit basis or on the entire code word after it is shifted into memory 20. If upon comparison between the master code and the key code, there is correspondence of all bits therebetween, logic 26 provides an output signal to actuate the associated lock or other utilization means.

It will be appreciated that the lock 16 can be associated with any utilization means which is to be key operated, such as a locking mechanism for a door, vault or the like, or electrical apparatus. If there is a lack of correspondence between one or more bits of the master code and the key code, logic 26 provides an alarm signal indicative of an erroneous key code. The alarm signal can immediately actuate an alarm indicator or can be employed with suitable counting circuitry to permit a selected number of decoding attempts before an alarm is actuated. Delayed alarm actuation is useful, for example, to prevent a transient condition, such as momentary contact loss, from causing an alarm.

For some purposes an alarm signal is not needed to indicate detection of an erroneous key code, and in this event the logic circuitry 26 will provide an output signal to the utilization means if a proper key code is detected, and this output signal will not be provided upon detection of an erroneous key code. The production of an output signal indicative of an alarm condition is desirable, however, for many purposes. The security of the present system is considerably enhanced by the feature by which any attempt to employ an incorrect key code will serve to actuate an alarm. There is thus no opportunity to try different possible key codes in an attempt to actuate the lock, as the first wrong code will cause an alarm indication. It is possible to cause readout of data stored in memory 12 to ascertain its data content and thereby reproduce the key code. However, a key code can be employed as part of the data in memory 12 such that interrogation thereof will not reveal the key code. For example, data stored in memory 12 can be configured such that the code itself is contained at predetermined bit positions within a longer stored word and coding schemes can be selected with are extremely difficult if not practically impossible to decode. The length of the data word stored in memory 12 also serves to enhance security of the system; for example, a 32 bit memory permits 2³² possible coding combinations.

The necessary correspondence between the key and master codes required to produce an output utilization signal is of course a matter of choice to suit operational circumstances. For high security, it will usually be desired to require exact correspondence between a key code and master code to produce an output signal. However, for many purposes a key code can be considered correct even though some small numbers of bits are different than the corresponding bits of the master code. In other words, the key code need only be correct to an intended degree of tolerance.

System security can be enhanced by use of a key which communicates data to the lock circuit only upon receipt by the key of a proper interrogation code. Such a technique is illustrated in FIG. 2 which shows a first memory 34 coupled to a comparator 36 which, in turn, is coupled to a second memory 38. Each of the memories 34 and 38 are typically integrated circuit shift registers as described above. The memory 34 contains a predetermined code word which is compared in com3,859,634 parator 36 with an enable code which can be provided by the lock circuit. Upon detection by comparator 36 of correspondence between the enable code and the code stored in memory 34, a read command is provided to memory 38 to cause readout of a different code stored in memory 38. The code word from memory 38 is operative to actuate the lock after correspondence is established between this code and the master code stored in the lock circuit, as described above.

Upon interrogation of the key by an enable code which does not compare with the preprogrammed data in memory 34, comparator 36 can provide an alarm signal to the associated lock circuit. An alarm indication can also be provided, as above, upon non-identity between the master code in the lock and the code from memory 38. The technique of FIG. 2 thus affords a dual encoding arrangement which is of a higher order of security than the coding arrangement of FIG. 1. Additional levels of coding can also be readily provided according to the principles of this invention since small, low power digital circuitry can achieve the key function.

An alternative embodiment of the key circuitry of FIG. 2 is depicted in FIG. 2A wherein the key contains a memory 35 operative to receive the enable code and to convey this code to a comparator 37 which also receives a key code stored in memory 39. The output of comparator 37 is connected to an encoder 41, the output of which serves as the key output signal. Upon receipt of an enable code which is of requisite identity to the key code, the comparator 37 provides a signal to encoder 41 which, in turn, provides a coded output signal for application to the associated lock or other utilization means. The signal from comparator 37 can itself be the key output; however, in this latter instance the security of the system is diminished as the noncoded comparator output signal may be wrongfully duplicated.

In addition to storage in the key of a key identification code for gaining access to the associated lock, the key can also contain additional data representing the identity of the particular key, an account number or the like. The system disclosed in FIG. 1 can be modified as indicated in FIG. 3 to accommodate such additional data. Referring to FIG. 3, data from a key is composed of a first word representing the key code and a second word representing other data such as a key number. This data is applied from the key to a pair of memory stages. The key code word is stored in memory 20A while the other identification code is stored in 20B. The key code is compared with the master code in comparator 22 in the same manner as described hereinabove.

The output of the comparator is applied to one input of an AND gate 23. The output of memory 20B is applied to a decoder 25, the output of which is applied to the second input of AND gate 23. The code processing cycle is governed by a counter 21 operative in response to clock signals from clock 28, the counter providing a timing sequence sufficient for loading data from the key into memories 20A and 20B. Upon identification of the key code in comparator 22, an output signal is provided by AND gate 23 for actuation of the lock. Failure to detect a proper key code will prevent a lock actuation output. In the embodiment of FIG. 3 failure to detect a proper code in memory 20B will also prevent lock actuation. It is evident that an output signal from decoder 25 representative of the additional identity code stored in the key can be employed to record such key identity, for example to denote the time that a particular key was employed with the associated lock.

The key can also be coded for use with a master key system in which one or more tiers of master keying can operate associated classes of locks, while non-master keys can operate only specific associated locks. Referring to FIG. 4, there is shown, in typical embodiment, 10 lock circuitry operative to decode two or more individual codes contained within different key data memories. A data memory, such as a shift register 43, receives a key code from an associated key and has a first group of outputs from selected bit positions of memory 15 43 connected to a decoder 45, and a second group of outputs from selected bit positions connected to a second decoder 47. Other decoders can be similarly connected to predetermined bit positions of memory 43 depending upon the levels of master coding desired.

The output of each decoder 45 and 47 is coupled to logic circuitry 49, the output of which is the lock output signal.

In operation, the detection of a predetermined code in the bit positions associated with decoder 45 causes 25 the decoder to provide an output signal to logic 49 which, in turn, produces an output signal for lock actuation or other utilization purposes. Similarly, detection of a code in the bit positions associated with decoder 47 causes this decoder to provide an output signal to ³⁰ logic 49 for production of the output signal. It will thus be appreciated that keys containing either code will cause production of the output signal. Such multiple key codes, each decodable by the lock circuitry, can be employed in various master lock systems in which dif³⁵ ferent classes of locks can be actuated by different classes of keys, or more generally, various levels of security provided by the different levels of key coding. As a further alternative, the logic 49 can also be implemented to provide respective output signals in response to re⁴⁰ spective signals from each decoder to thereby indicate which key code has been detected.

A more particular embodiment of the invention is illustrated in FIG. 5. The key includes and has disposed therein a shift register 40 typically of the monolithic in⁴⁵ tegrated circuit type and capable of storing a predetermined number of data bits which comprise a key code. Register 40 is powered by a suitable battery 42 which is also of small physical size to fit within a key element. Data from shift register 40 is communicative with the ⁵⁰ lock circuit by way of a data gate 44 operative to recirculate data back into shift register 40 to retain the same key code, or to load register 40 with new data to provide a new key code, as will be described.

Data from register 40 is applied to a digital compara⁵⁵ tor 46 which also receives information from a master code register 48. Register 48 contains a master code word as provided by a master code selector 50, which is used for comparison with the key code contained in _n the shift register 40. System timing is governed by a ⁶⁰ clockk 52 which is started upon receipt of a start signal from a key insertion detector 32, such as described above. Detector 32 also energizes key clamp 33 which captures the key in the lock during the identification cycle. A clock provides two output signals, labeled re⁶⁵ spectively φΐ and φ2, which are clock pulses recurring at the same clock rate but shifted in phase one from the other by a predetermined amount, typicality 180°. The

3,859,634 clock pulses φΐ are advanced in phase from the clock pulses φ2 and are employed to control data bit transitions, while the delayed clock pulses φ2 are employed to control bit comparisons. Thus, it will be appreciated that bit comparisons are accomplished at the midpoint 5 of a bit interval to assure that such comparisons are performed after transients which may occur during bit transitions.

The clock pulses φΐ are applied to register 48 and also to a counter 54 operative to count the number of 10 bits shifted out of register 48. By means of a counter decoder 56, the last bit shifted out of register 48 is recognized to denote the end of the code comparison process. The key insertion detector 32 is operative to clamp the key in the lock to prevent its premature re- 15 moval prior to completion of the decoding process. Detector 32 also provides a signal to flip-flop 58 to set the flip-flop to one logical state, the output signal thereof being applied to one input of an AND gate 62. Data in key register 40 and master register 48 are clocked out 20 bit by bit by clock pulses φΐ and are compared bit by bit in comparator 46. The comparator is operative to provide a first output, say zero, if the bit from the key register is identical to the bit from the master register, and to provide a second output, say one, if there is not 25 correspondence between the received data bits. The output of comparator 46 is couopled to an AND gate 60 which also receives the clock pulses φ2, the output of gate 60 being applied to the reset input of flip-flop 58. The output of flip-flop 58 is coupled to one input ³⁰of an AND gate 62, the other input of which is the output signal from counter decoder 56 for enabling gate 62.

Upon correspondence between a data bit from key register 40 and a data bit from master register 48, AND ³⁵gate 60 will remain disabled and no reset signal will be applied to flip-flop 58. Thus, flip-flop 58 remains in its set state so long as there is identity between the key code and the master code providing an output signal to gate 62. Upon detection of the last bit of the master ⁴⁰code by decoder 56, an output signal is provided for lock actuation. The signal from decoder 56 is also employed to release key clamp 33 to permit removal of the key from the lock. The output signal from gate 62 is the system output signal for activating the associated ⁴⁵lock or other utilization means upon detection of a proper key code.

If, during comparison of any bit of the key code, a lack of identity is found between this bit and the associated bit of the master code in register 48, the output ⁵⁰signal from comparator 46 will cause enabling of AND gate 60 and consequent resetting of flip-flop 58 which causes removal of the flip-flop output signal to gate 62. No actuation signal can be provided by reason of the disabling of gate 62. An output signal from gate 60 is ⁵provided only upon detection of an error between a bit of the key code and a corresponding bit of the master code, and this output signal is also employed to activate an alarm circuit 64 to indicate detection of an erroneous key code. Upon sensing of an alarm condition, a stop signal can be generated by alarm circuitry 64 to stop clock 52 and discontinue the decoding process and to prevent the release of the key clamped in the lock by clamp 33. ₆₅

In one mode of operation, the master code stored in register 48 is recirculated back into this register so that the code is available for subsequent data comparison.

Similarly, the code in shift register 40 is recirculated therein by means of data gate 44 so that the same key code can later be employed. To further enhance the security of the novel lock system, however, the invention is also operative in another mode wherein the code residing in shift register 40 and master code 48 is replaced with a new code. Such new code can be replaced on a regular basis or from time to time depending on particular security requirements.

To employ such a new code, the output signal of gate 62 provided upon correspondence between the key code and the master code, is applied via a switch 63 to set a flip-flop 66, one output of which is employed to energize a timing circuit 67 which, in turn, provides a start signal to clock 52. The other output of flip-flop 66 is applied to an AND gate 68 which also receives clock signals φΐ. The output of gate 68 is applied to the clock input of a new code register 70 which has stored therein a new data code provided by a new code selector 72. The output of new code register 70 is applied to data gate 44 for coupling of such new data into key shift register 40. The new data is also applied to the master code register 48 for use in a subsequent data comparison. In this latter mode of operation, clock 52 is enabled for only a sufficient period of time determined by timing circuit 67 to permit shifting of the new code data into the key shift register 40 and to prevent reinstitution of the digital comparison process until the key is again inserted into the lock at a subsequent time.

The new code selector 72 can be implemented in several different ways and can include a binary word generator which is manually actuable, such as by an array of switches, or automatically actuable for example by means of a computer. By use of a digital computer, a new key code can be provided from a random number sequence generated by the computer such that the code is readily identifiable only in computer memory and need not be known to operating personnel in order to alter the key code. The master code can be updated immediately after completion of a particular decoding process or, alternatively, can be updated on a periodic basis. For example, in some circumstances it is desirable to reprogram the key code immediately after use of the key and to reprogram the master code on a daily basis to permit use of the key only once per day.

Rather than employing a separate clock signal for conveying data in the present system, a self clocking code can be employed which is advantageous in eliminating the need for a separate clock line and associated terminals. Key circuitry operative in a self clocking mode with associated lock circuitry is depicted in FIG. 6. A data memory 51 is employed to store a predetermined code and has an output coupled via an AND gate S3 to an encoder 55 which also receives clock signals from a clock 57 within the key. The encoder is, for example, a Manchester encoder for providing a self clocking output signal for conveyance to the associated lock circuitry. The key clock 57 also provides clock signals to memory 51 and to a counter 59 operative to provide a stop signal to clock 57 after a predetermined number of clock signals.

A self clocking data stream from the lock circuitry is received by a Manchester decoder 61 operative to provide decoded data to memory 63 as well as clock signals thereto. Memory 63 is operative to convey the data therein in parallel to a comparator 65 which also received parallel data from a memory 67 which stores

3,859,634 a predetermined key code. Upon detection of an identical code contained in memories 63 and 67, comparator 65 provides a trigger signal to clock 57 and also to gate 53 as an enable signal therefor.

The trigger signal initiates a clock cycle to enable the shifting out of the code in memory 51 which is conveyed via gate 53 to the encoder 55 for conversion to a self clocking format for transfer to the lock circuitry. Gate 53 is enabled by the trigger signal form comparator 65 for a sufficient period of time to permit transfer of data from memory 51. The clock cycle is discontinued by a stop signal from counter 59. The data in memory 51 remains in storage either by being recirculated therein or by use of a non-volatile memory in which data is not destroyed upon readout. It will be evident that the embodiment of FIG. 6 is similar to that of FIG. 3 wherein a double coding arrangement is employed within the key to enhance system security. The embodiment of FIG. 6 can also be employed with a separate clocking signal, in which case the Manchester encoder and decoder would not be necessary.

As described above, the circuitry of the key can typically be powered by a small battery source. Alternatively, it may sometimes be desirable to supplement the battery source or to entirely replace the battery source by power applied externally of the key. This can be accomplished as shown in FIG. 7 wherein the lock circuit is operative to electromagnetically convey power to the key circuitry. The lock circuit 69 includes means for providing energy to the primary coil 71 of a transformer 99 for propagation of electromagnetic energy which is received by a secondary coil 73 which is part of the key and which has its respective ends coupled via respective diodes 75 and 77 to a resistor 79, and thence to the key logic circuitry 81. The center tap of coil 73 is also connected to a power input of logic circuitry 81, and a capacitor 83 is connected across the power inputs thereto. A code signal input to the key logic circuitry 81 is provided by an input line from the junction of diodes 75 and 77. A battery 85 can also be connected across the power input leads as illustrated.

By the circuit of FIG. 7 both energizing power and signals are applied to the key. Typically, a pulse modulated carrier is employed to convey energy and information to the key, with power being detected by means of the rectifier and associated filter, and with the signal being separately coupled to the key logic. Various other modulation techniques, per se well known, can also be employed to provide energy and data to the key circuitry. The battery 85 is employed to provide power to the key data memory or memories to retain the information stored therein in the absence of connection to the lock circuit. If, however, non-volatile memories are employed, the battery 85 is not required. Coupling of energizing power from the lock to the key circuit can also be otherwise accomplished, such as by photoelectric coupling.

The key can be implemented in a variety of mechanical configurations to suit particular operating requirements. The key can, for example, be in a form much like an ordinary mechanical key, as illustrated in FIG. 8. In this instance the key 80 is formed of a nonconductive material such as an epoxy and has the memory encapsulated therein. The battery, in the form of a small button cell, is contained within a battery compartment located in the handle portion of key 80, access thereto being provided by a removable cover 84. Electrical connection is provided at the distal end of key 80 by means of four conductive bands 86 provided on the end thereof, each being of generally U-shaped configuration as illustrated.

The key is inserted within a keyway 88 of an associated lock, the contact bands 86 being cooperative with an electrical connector 87 disposed at the inner end of the keyway to provide connection between the key and the lock circuitry. Also disposed at the inner end of the keyway is a microswitch 90 which includes an actuation arm 92 disposed for actuation by the end of key 80 upon its insertion into the lock. The switch 90 is part of insertion detector 32 (FIG. 1) and is operative to provide a key insertion signal to the system clock for commncement of the key decoding process. A notch 94 is provided in one side of key 80 and is cooperative with a rod 94 associated with solenoid 96 to prevent removal of the key during the decoding process. The solenoid 96 is typically energized by a signal from key insertion detector 32.

As described hereinabove, an alarm signal can be provided by the invention in the event that there is lack of comparison between the key code and the master code of the lock. Premature withdrawal of the key could also cause an alarm condition and to prevent such an occurrence, the key is clamped within the lock by solenoid 96 until completion of the decoding cycle. The key can also be retained in the lock in the event that an erroneous code is detected to prevent its removal in such event. The key code can be arranged such that the first bit to be read out of the key is always at ground potential such that ground potential exists on all terminal contacts 86 when the key is not in use, to thereby prevent accidental shorting of the key which could destroy the stored data. The key terminals could alternatively be deactivated when the key is not in use by a suitable switch arrangement.

Electrical connection between the key and associated lock can also be provided by other than electrical contacts such as illustrated in FIG. 8. Electrical connection can also be made by noncontacting means such as inductive or photoelectric coupling. One such noncontacting coupling is shown in FIG. 9 wherein the key logic 87 has its data output connected to a light emitting diode 89 or other suitable light source, and its data input connected to a photosensor 91. The lock logic 93 similarly has its data input connected to a photosensor 95 and its data output connected to a light source such as a light emitting diode 97.

In use, with the key in operative association with the lock, the photosensor 91 is in light receiving relationship with light emitting diode 97, while the photosensor 95 is in light receiving relationship with the light emitting diode 89. The key code provided in the form of electrical pulses by logic 87 is applied to light emitting diode 89 which provides corresponding light pulses for receipt by photosensor 95 which, in turn, produces electrical pulses to logic 93 for decoding in the manner described above. Similarly, signals from the lock logic 93 are transduced photoelectrically between light emitting diode 97 and photosensor 91 for application to key logic 87. The signals from logic 93 can be data applied to the key data memory for re-entering a new key code or can be an enabling signal for initiating the key decoding process depending upon the specific embodiment. In the event that a separate clock signal is em3,859,634

12 ployed, this clock signal can also be photoelectrically coupled from the lock to the key.

From the foregoing it will be evident that an electronic lock system has been provided which is both reliable and highly secure and which can be constructed in 5 an efficient and commercially realistic manner. Various modifications and alternative implementations will occur to those versed in the art without departing from the spirit and true scope of the invention. For example, data can be conveyed between the key and the lock in 10 a parallel rather than a serial manner, and various levels of coding can be provided to suit the desired level of security. The electronic circuitry and its mechanical housing can take a wide variety of forms adapted to specific installation requirements. Accordingly, it is not 15 intended to limit the invention by what has been particularly shown and described, except as indicated in the appended claims.