Remote control method using variable ID code

Abstract: In a remote control system, each time a transmission code is transmitted, a rolling code (R2-R0) having a prescribed bit configuration is cumulatively varied (S30). An operation process (S40) is performed between each bit data item of the rolling code and each corresponding bit data item of the ID code (I5-I0), whereby each bit data item of the ID code is varied in correspondence with the rolling code, thus setting a variable ID code. Since the ID code itself which is contained in the signal is also varied in correspondence with the variable code, the fixed portion contained in the signal is decreased with the result that the ID code is almost infinitely widely varied. Accordingly, it becomes almost impossible to decode the ID code even if it is intercepted.

Description: The present invention relates to an encoding method for a remote control system which uses a variable ID (identification) code and is used in, for example, a protection system such as a wireless door lock control system for a vehicle. Conventionally, in a remote control system which is adopted in, for example, a wireless door lock control system, an individual ID code is set in a coded signal transmitted and received through radiocommunication, and the coded signal containing this ID code is transmitted from a transmitter. The transmitted coded signal is received by a receiver, and the ID code contained in the received coded signal and an ID code preset in the receiver are compared with each other. Then, when both ID codes coincide with each other, the system operates the object to be controlled to thereby prevent another from using the ID code signal. However, it has in recent years been reported that the above ID code can be copied by an interceptor device which intercepts an ID code contained in the coded signal transmitted through radiocommunication, and that an unauthorized person other than the authorized user can use the signal without authorization by transmitting the same ID code. This means that the security of the conventional type of remote control system directed only to transmitting and receiving an individual ID code can be breached. As a countermeasure against this, for example, Japanese Unexamined Patent Application Laid-open No. H1-278671 discloses a remote control system which comprises, in addition to a fixed ID code, a code-number cumulative alteration means for cumulatively altering the code number in correspondence with the transmission frequency according to a prescribed sequential order. Namely, in the remote control system disclosed in the above publication, a code number (rolling code) which is altered in correspondence with the transmission frequency according to a prescribed sequential order is added, in addition to the ID code, to the transmission code, and this code number is utilized for judgement of a transmission signal. For this reason, even if the transmission signal is copied by the transmission signal interceptor device, mere transmission of such copied signal cannot use the ID code signal because code information is altered for each transmission and this altered information is utilized for determination of the transmission signal. However, in the conventional system, although the system is comprised of a variable code number, the ID code per se that is fixed is still contained in the transmission signal. Therefore, if the transmission signal is intercepted many times by the ID code interceptor device, decoding thereof will be possible by determining that the code which is continuously fixed is the ID code and the varying code is the rolling code and by finding the regularity in the variation of the varying code. Namely, since the information of the ID code which is fixed exists in the transmission signal, an unauthorized person who uses it without authorization can relatively easily determine what portion of the signal is the ID code and what portion of the signal is the rolling code. Further, if the regularity of a variable portion of the code other than the ID code has been found after noticing this variable portion, the unauthorized user would be able to use the ID code signal. An encoding method according to the preamble of claim 1 is known from document EP-A-0 570 761. This document discloses an encoding method for a remote control system having a transmitter for transmitting a transmission code including an ID code prepared by encoding a specific identification information and a receiver which is receiving the transmission code transmitted by the transmitter, decoding the ID code and outputting an instruction which causes the operation of a control object if the decoded ID code is coinciding with a preset ID code. In this known method, a rolling code which is composed of a prescribed number of bits is cumulatively varied each time the transmitter is transmitting the transmission code; then an operation process is performed with respect to each bit of the rolling code and each corresponding bit of the ID code in order to vary each bit of the ID code in correspondence with the rolling code; finally a transmission code including the ID code is produced in a rearranged form. A disadvantage of this known system has to be seen in that it is necessary to derive the rolling code in the receiver by means of a complicated synchronization method. Therefore, this known system needs an expensive logic circuit so as to perform the synchronization. Furthermore, the synchronization is time consuming so that the remote control may suffer from a certain time delay. It is the object of the present invention to improve an encoding method according to the preamble of claim 1 in such a way that it can be performed with no substantial time delay and with an inexpensive circuit without, however, to decrease the security of the transmission. This object, according to the invention, is solved by the advantageous measures of the characterizing part of claim 1. There is also provided a decoding method according to claim 5. According to the present invention, in a remote control system, each time a transmission code is transmitted, a rolling code composed of a prescribed number of bits is cumulatively varied. Then, each bit data item of the rolling code and each corresponding bit data item of an ID code are operation processed thereby to vary each bit data item of the ID code in correspondence with the rolling code, thus setting a variable ID code. Namely, the ID code in the transmission signal is also varied in correspondence with the rolling code and therefore substantially the entire information in the transmission signal is variable information. Thus, what portion of the signal is the ID code and what portion thereof is the rolling code cannot be discriminated. Further, it is almost impossible to find a regularity in the variation of the rolling code. Accordingly, it is possible to prevent an unauthorized person other than the authorized user from using the signal without authorization. Preferably, the variable ID code is set by combining the bits of the rolling code in the same number as that of the bits of the ID code according to a prescribed combination setting and performing an exclusive-OR operation between each bit data item of the combined rolling code and each corresponding bit data item of the ID code. Namely, by utilizing the exclusive-OR operation, coding and decoding processes are more efficiently performed compared with various other operation processes. Further, the rolling code is cumulatively varied and the restored rolling code and the rolling code reset in a receiver are compared with each other for determining whether or not the rolling code is correct. Namely, since the degree of coincidence between both rolling codes as well as that between both ID codes is determined by comparison, the level of security is excellent. In the case where it has been determined that the restored rolling code is correct, the following effect is brought about by storing the restored rolling code. That is, even when the rolling code of the transmitter has preceded the rolling code of the receiver (for example, where the rolling code has not been received despite having been transmitted), a correspondence therebetween can be attained. Preferably, a plurality of kinds of bit-data rearranging order settings are provided as the prescribed bit-data rearranging order settings. Although a larger space is needed as the memory space since a plurality of kinds are set, the transmission code is varied in a more complex manner, whereby the difficulty of decoding increases. Further, if the prescribed bit-data rearranging order setting is selected by a random number, the transmission code cannot be decoded unless a relevant random number is obtained. More preferably, it is determined whether or not a prescribed time period has passed from the start of transmission. Where it has been determined that the transmission time period is not longer than the prescribed time period, the bit data items are rearranged according to a relevant prescribed bit-data rearranging order setting as preset, and the rearranged code is stopped from being added to the transmission code. Where it has been determined that the transmission time period is longer than such prescribed time period, the relevant prescribed bit-data rearranging order setting is updated and the bit data items are rearranged according to this updated prescribed bit-data rearranging order setting, and the updated rearranged code is added to the transmission code. In other words, only when the transmission code has continued to be transmitted for at least the prescribed time period, the relevant prescribed bit-data rearranging order setting is updated. As a result, by appropriately changing the transmission time period, the user can freely change the bit-data rearranging order setting. In addition, if the user changes this once, he can prevent the rearranged code from being added to the transmission code from the next time onward only if the transmission time period is not longer than the prescribed time period. Therefore, the transmission code has no information due to the bit-data rearrangement, so that even if the transmission code has been intercepted, decoding thereof becomes virtually impossible. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a schematic structural diagram illustrating an embodiment of the present invention; Figs. 2A and 2B are flowcharts illustrating operations of a transmitter and a receiver illustrated in Fig. 1, respectively; Fig. 3 is a schematic view illustrating states of codes at a transmission-code composing time; Fig. 4 is a table illustrating patterns according to which the orders of bit-position rearrangement are set; Fig. 5 is a schematic view illustrating states of codes at the transmission-code decoding time; Fig. 6 is a flow chart illustrating the operation of the transmitter, in the case where a sorting code is added after the passage of a prescribed time period; Fig. 7 is a flow chart illustrating the operation of the receiver, in the case where a sorting code is added after the passage of a prescribed time period; and Fig. 8 is a table illustrating patterns according to which the bit-position combinations are set. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described hereafter with reference to the embodiments illustrated in the drawings. [First Embodiment] Fig. 1 is a structural diagram representing a remote control system (transmission and reception system) which is applied to a protection system such as, for example, a wireless door lock control system for a vehicle. In Fig. 1, reference numeral 1 denotes a transmitter, in which there are provided switches 12-1, 12-2, ---, 12-n for performing remote control operations on their respective different functions (for example, door lock, opening/closing of trunk, seat position setting, etc.). Signals generated as a result of the switch operations are input to a microprocessor (MC) 11. To this microprocessor 11 there is connected an EEPROM 19, in which there is stored an ID code specific to the transmitter 1. RAM (not illustrated) is formed in the microprocessor 11 and this RAM stores a rolling code the content of the information of which varies each time it is transmitted, as well as with data for transmission code production. Further, an oscillator circuit 14 and an FM modulator circuit 15 are connected to the microprocessor 11 so as to FM modulate a transmission code produced in the microprocessor 11 and transmit it from an antenna. Meanwhile, a receiver 2 is provided with receiver circuitry for demodulating the transmitted signal from the transmitter 1, which receiver circuitry is formed by a radio frequency amplifier circuit 25, local oscillator 24, mixer circuit 26, intermediate frequency amplifier circuit 27, and demodulator circuit 28. The output signal as demodulated by this receiver circuitry 2 is input to a microprocessor 21. This microprocessor 21 produces an ID code and rolling code from the output signal as demodulated according to previously determined processes. An EEPROM 29 which stores a code corresponding to the ID code specific to the transmitter 1 is connected to the microprocessor 21. Further, control objects 3-1, 3-2, ---, 3-n (for example, actuators for performing door locking, trunk opening/closing, seat position setting, etc.) are connected to the microprocessor 21 via drive circuits 23-1, 23-2, ---, 23-n, respectively. The control objects 3-1, 3-2, ---, 3-n are operated according to signals from the microprocessor 21. Next, operation of the transmitter 1 and receiver 2 will be described according to the flow charts illustrated in Figs. 2A and 2B. The processes illustrated in the flowchart are processes which are executed by the microprocessors 11 and 21 respectively provided in the transmitter 1 and receiver 2. Firstly, the operation of the transmitter 1 will be explained. In step 10, the operation is in standby until it is determined that any one of the switches 12-1 through 12-n has been operated, and when it is determined that any one of such switches has been operated, the operation proceeds to step 20. In step 20, a 4-bit random number (C3, C2, C1, C0) is generated and a bit-data rearranging order corresponding to the thus generated 4-bit random number is set according to the contents of a table shown in Fig. 4. In this embodiment, it is assumed that, for example, a 4-bit random number (0, 0, 0, 0) has been generated and an uppermost stage pattern shown in the table in Fig. 4 has been set for the bit-data rearranging order. Next, in step 30, updating of the rolling code is performed. This rolling code is a variable composed of n bits (Rn-1 to R0), which variable is updated each time the rolling code is transmitted. Although in this embodiment it is assumed that the rolling code is a variable composed of 3 bits (1, 0, 0) and varies by +1 each time it is transmitted, the present invention is not limited thereto but any manner of variation may be available as long as the rolling code varies in accordance with a prescribed rule. Further, in step 40, exclusive-OR operation is performed between the rolling code and the ID code. Specifically, as illustrated in Fig. 3, a previously determined bit combination (with no regularity), e.g. a 6-bit combination (R1, R2, R1, R0, R0, R2) is set for the rolling code, whereby exclusive-OR operation is performed between each bit value thereof and each corresponding bit value of the ID code. The ID code is a code specific to the transmitter 1 and stored in EEPROM 19 as mentioned above and that this ID code is a fixed value composed of m bits (Im-1 to I0). In this embodiment, a 6-bit value (0, 0, 1, 0, 1, 1) is set for this ID code. Therefore, in step 40, exclusive-OR operation is performed between the ID code (0, 0, 1, 0, 1, 1) and the combination rolling code (0, 1, 0, 0, 0, 1), so that an exclusive-OR of (0, 1, 1, 0, 1, 0) is set. Next, in step 50, the exclusive-OR result set in step 40 and the rolling code are rearranged according to the bit-data rearranging order set in step 20. Specifically, as illustrated in Fig. 3, the (0, 1, 1, 0, 1, 0) and (1, 0, 0) are rearranged according to the bit-data rearranging order (I'3, R2, I'0, R0, I'2, I'5, R1, I'4, I'1), whereby (1, 1, 0, 0, 0, 0, 0, 1, 1) is set. Next, in step 60, format bits (start bits, stop bits), function bits, and a parity bit are added to the code rearranged in step 50 and further the 4-bit random number (C3, C2, C1, C0) is added to thereby compose a transmission code. Specifically, as illustrated in Figs. 3 and 4, stop bits are disposed and then the rearranged code is disposed in such a manner as to be sectioned by the start bits. Further, the function bits, parity bit, and 4-bit random number (which indicates information on the bit-data rearranging order) are added to thereby compose a transmission code. The format bits are those for synchronizing data transmission while, on the other hand, the function bits (K1, K0) are those which represent which one of the operation switches has been operated. The parity bit is one for detecting a transmission error. Next, in step 70, the transmission code which has been composed in step 60 is output to the FM modulator circuit 15. As a result, the transmission code is FM modulated and transmitted to the exterior of the transmitter 1 as a feeble wave. The above-mentioned series of steps are intended for performing the processes to be executed in the transmitter 1 when one of the operation switches has been once operated. Therefore, when that operation switch is again depressed, the processes in steps 20 through 70 are again executed and, in this case, the 4-bit random number and the rolling code are changed. The transmission code to be transmitted next is illustrated in the simplified manner in the lower portion of Fig. 3A, provided, however, it is assumed that the 4-bit random number is identical. Next, the operation of the receiver 2 will be explained with reference to Fig. 2B. In step 110, the operation is in standby until the transmission code from the transmitter 1 is received by the receiver 2. When the transmission code has been received, the operation proceeds to step 120. In step 120, the function bits, rearranged code (exclusive-ORed code + rolling code), and 4-bit random number which have been disposed at their respective prescribed positions are respectively drawn away from the transmission code, whereupon the rearranged code is restored to its original arrangement order according to the 4-bit random number, to restore the exclusive-ORed code and the rolling code. Specifically, as illustrated in Fig. 5, the rearranged code (1, 1, 0, 0, 0, 0, 0, 1, 1) is restored to its original arrangement order according to the 4-bit random number (0, 0, 0, 0) to restore the exclusive-ORed code (0, 1, 1, 0, 1, 0) and the rolling code (1, 0, 0). Next, in step 130, the above-mentioned exclusive-ORed code is subjected to exclusive-OR operation by using the rolling code to restore the ID code. Specifically, as illustrated in Fig. 5, exclusive-OR operation is performed between each bit value of the same rolling code bit combination as that exclusive-ORed in step 40, i.e. 6-bit combination (R1, R2, R1, R0, R0, R2) and each corresponding bit value of the exclusive-ORed code. Namely, the ID code (0, 0, 1, 0, 1, 1) is restored from the exclusive-ORed code (0, 1, 1, 0, 1, 0) and the bit values of the 6-bit combination value (0, 0, 1, 0, 1, 1) . It is assumed that the same 6-bit combination rolling code is set in both the transmitter 1 and the receiver 2. Next, in step 140, it is determined whether or not the ID code set in the EEPROM 29 and the ID code of the transmission code restored in step 130 coincide with each other. If both coincide, the operation proceeds to step 150. If there is no coincidence between the codes, the operation returns to step 110 in which the operation is placed in standby. Further, in step 150, comparing the rolling code restored in step 120 with the previously stored rolling code, it is determined whether or not the amount of change of the restored rolling code relative to the previous rolling code is in a range of from +1 to +X. If the amount of change is in this range, it is determined that the present rolling code is correct. Thus, the operation proceeds to step 160. If the amount of change is outside the range, the operation proceeds to step 110 in which the operation is placed in standby. At this time, if the transmission code from the transmitter 1 is received by the receiver 2 each time it is transmitted, the amount of change of the rolling code to be determined by comparison in the receiver 2 may be limited to the value of the previous rolling code plus 1. However, since in the case where the transmitter is operated without being accompanied by reception of the transmission code by the receiver 2, only the rolling code on the transmitter 1 is updated, such a permissible range is provided which could cope with such a case as well. Namely, assuming that the value of the rolling code restored from the transmission code is represented by ri and the value of the previous rolling code is represented by ri-1, if "ri-1 + 1 ≤ ri ≤ ri-1 + X", it is determined that the rolling code is normal. Next, in step 160, the rolling code restored from the transmission code is stored in a RAM and the rolling code as stored is updated thereby. As a result, for example, where only the rolling code on the transmitter 1 is updated but the value of the rolling code restored from the transmission code falls within the permissible range and is determined as being normal, an error occurs between the rolling code set in the transmitter 1 and that set in the receiver 2. However, since in such a case the rolling code on the receiver 2 is updated by the rolling code restored from the transmission code, the rolling code on the transmitter 1 and that on the receiver 2 coincide with each other. Further, in step 170, the control objects 3-1, 3-2, ---, 3-n are operated in corresponding relation to the function bits (K1, K0) set in the transmission code via the drive circuits 23-1, 23-2, ---, 23-n. Although this embodiment has been directed to controlling several control objects, a transmission code with no function bit can also be realized by providing a single function as the function of the system. [Second Embodiment] This embodiment is directed to determining whether or not a transmission signal has continued to be transmitted for a prescribed time period (whether or not the switch has been continually depressed for the prescribed time period) and, where the transmission signal has continued to be transmitted for at least the prescribed time period, updating (re-registering) the bit-data rearranging order setting registered on the receiver side and to this end transmitting a new bit-data rearranging order setting from the transmitter 1 to the receiver 2. The operations of the transmitter 1 and the receiver 2 will now be explained according to the flow chart illustrated in Figs. 6 and 7, in which the same reference numerals are used to denote the same or similar steps as in the first embodiment. First, in step 10 through 70, the similar processes are performed as in the first embodiment. That is, it is determined whether or not any one of the switches has been depressed as in the first embodiment. Where the switch has been depressed, the rolling code is updated and an exclusive-OR operation is performed between the rolling code and the ID code. Then, the resulting code bit data items are rearranged according to a relevant bit-data rearranging order setting to thereby perform a transmission-code transmission processing. However, the operation of setting the bit-data rearranging order according to a 4-bit random number and the operation of adding this 4-bit random number to the transmission code are not included among the operations in steps 10 through 70. Namely, if the switch has only been depressed, the bit-data rearranging order setting remains as it previously was and is not updated. Therefore, the bit-data rearranging operation is performed according to the same bit-data rearranging order setting as in the previous transmission. Therefore, with no 4-bit random number being added to the transmission code, the receiver 2 restores according to the previous bit-data rearranging order setting. Namely, data corresponding to this 4-bit random number need not be added to the transmission code. Accordingly, in usual uses (where the switch is continually depressed, for example, for only several seconds or so), it is impossible for unauthorized person to decode it merely by interception thereof because data corresponding to the bit-position rearranging order setting is not contained in the transmission code. However, if only the above-described processing is performed, the bit-data rearranging order setting remains fixed. Accordingly, there is the possibility that it may be found through tens of interceptions that the bit-data rearranging order setting involves a certain standard or rule of regularity. This problem is settled by updating (re-registering) the bit-data rearranging order setting and varying such regularity. Specifically, in step 80, where the transmission signal is continually transmitted for more than a prescribed period (where the switch is continually depressed for, for example, the prescribed time period from step 10), the processes in steps 20 and 90 through 93 are executed to thereby set a new bit-data rearranging order, according to which the bit-data items are rearranged. A 4-bit random number (C3, C2, C1, C0) resulting from the setting of the new bit-data rearranging order is added to the transmission code, thereby updating the bit-data rearranging order setting. On the other hand, as illustrated in Fig. 7, in step 121, on the receiver side it is determined whether or not 4-bit information corresponding to the relevant bit-data rearranging order setting is added to the transmission code. If such 4-bit information is added, the bit-data rearranging order setting to which it is added is stored in the memory and the previously stored bit-data rearranging order setting is updated thereby in step 122. Then, code restoration is performed according to the thus-updated bit-data rearranging order setting in step 124. If the above-mentioned 4-bit information is not added, code restoration is performed in step 123 according to the previous bit-data rearranging order setting as stored in the memory, whereby the receiver 2 maintains a corresponding relation to the transmitter 1. When the receiver 2 has succeeded in updating, the receiver 2 may have a structure wherein it transmits to the transmitter 1 a signal indicating that the receiver 2 has succeeded in updating, or a structure wherein it informs the user that the receiver 2 has succeeded in updating. As mentioned above, the second embodiment has a structure of determining whether or not the transmission signal has continued to be transmitted for the prescribed time period and, only when it has been continually transmitted for at least the prescribed time period, updating the bit-data rearranging order setting. As a consequence, it is possible for the user to freely change the bit-data rearranging order setting by appropriately altering the transmission time period. In addition, if the user once alters the transmission time period, any bit-data rearranging order is prevented from being added to the transmission code from the next time if the transmission time period is within the prescribed time period. For this reason, the transmission code has no information on the bit-data rearranging order, so that even when it is intercepted, decoding thereof is practically impossible. Additionally, in the above-explained embodiment, where the transmitter 1 transmits the transmission code, a plurality of kinds of bit-data rearranging order settings each including prescribed codes are set for the prescribed bit-data rearranging order settings as illustrated in Fig. 4. For this reason, a code which indicates what kind of bit-data rearranging order has been set has to be added to the transmission code. However, if one kind of bit-data rearranging order is set and the value thereof is set to be fixed, it becomes unnecessary to add to the transmission code a code indicating what bit-data rearranging order pattern has been set, although difficulty in decoding by interception is somewhat decreased. This makes it possible to simplify the production of a transmission code. In addition, in this case, since it is not necessary to provide bit-position rearranging order settings in the memory, it is possible to decrease the amount of data stored in the memory. On the other hand, in the above-mentioned embodiments, when exclusive-OR operation is performed, this operation is performed by setting the rolling code to a prescribed combination [6-bit fixed value (R1, R2, R1, R0, R0, R2)]. Therefore, the third embodiment illustrated in Fig. 8 may be also considered in which a plurality of combination patterns each including a prescribed code are set and, where the transmitter 1 transmits the transmission code, the transmitter 1 transmits this transmission code by adding to the transmission code a code which indicates according to what combination pattern the operation processing has been performed. By means of such embodiment, the code variation occurs in a more complex manner, thereby further increasing the difficulty in decoding by interception. Further, in the above-mentioned embodiments, explanation has been given with respect to an ID code having a 6-bit configuration and with the rolling code having a 3-bit configuration. However, the present invention is not limited thereto but permits the number of the above-mentioned code bits to be set at any given value according to its purpose. The present invention may be modified further in many other ways without departing from the spirit of the invention.

Claims: Encoding method for a remote control system, said system having a transmitter (1) for transmitting a transmission code including an ID code prepared by encoding a specific identification information and a receiver (2) which is receiving the transmission code transmitted by said transmitter (1), decoding the ID code and outputting an instruction which causes the operation of a control object (3-1 through 3-n) if the decoded ID code is coinciding with a preset ID code, said method comprising the steps of: [a] cumulatively varying (30) a rolling code which is composed of a prescribed number of bits each time the transmitter (1) is transmitting the transmission code; [b] performing (40) an operation process with respect to each bit of the rolling code and each corresponding bit of the ID code in order to vary each bit of the ID code in correspondence with the rolling code, and; [c] producing (60, 70) a transmission code including the ID code in a rearranged form; characterized by the steps of [c1] providing a prescription code prescribing the mode of rearrangement, said prescription code being changed either for each subsequent transmission or after lapse of a predetermined period; [c2] rearranging (50) each bit of the variable ID code and each bit of the rolling code according to the presently provided prescription code; and [c3] including the rearranged ID code and the rearranged rolling code into said transmission code. Method according to claim 1, characterized in that said prescription code is included into said transmission code each time it has been changed. Method according to claim 1 or 2, characterized in that , in step [b] , the bits of the rolling code are combined by a predetermined number of the bits of the ID code according to a prescribed combination setting and an exclusive-OR operation is performed between each bit of the combined rolling code and each corresponding one of the predetermined bits of the ID code so as to set the variable ID code. Method according to one of claims 1 to 3, characterized in that , in step [a] , a prescribed value is added or subtracted to resp. from the rolling code each time the transmitter transmits said transmission code, so as to vary the rolling code only in one direction, thereby cumulatively varying the rolling code. Method for decoding the transmission code encoded by an encoding method according to one of the preceding claims, characterized by the steps of [a] extracting (120), upon receipt of said transmission code from the transmitter (1), said rearranged code including said rearranged ID code and said rearranged rolling code and reversely rearranging the bits thereof according to the presently set prescription code so as to restore the ID code and the rolling code; [b] performing (130) an inverse operation with respect to the restored ID code and the restored rolling code to thereby restore the ID code in correspondence with the restored rolling code; and [c] comparing (140-170) the restored ID code and outputting said instruction which causes the operation of said control object (3-1 through 3-n) if the decoded ID code is coinciding with said preset ID code. Decoding method according to claim 5, characterized by the steps of [a] checking whether said prescription code is included in said transmission code; [b1] performing said rearrangement step in correspondence to the presently received prescription code, if a prescription code is included in said transmission code, and storing said prescription code; and [b2] performing said rearrangement step in correspondence to the stored prescription code, if no prescription code is included in said transmission code.

Inventors: HOTTA HISATAKA, MABUCHI TOMOJI, HOTTA, HISATAKA, MABUCHI, TOMOJI
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1995
Main classification: E05B49
IPC codes: H04Q9, E05B49, G07C9