Electrical device with input and output ports for changing the multiplex number of transmittal buses and system using the electrical device

Abstract: The same electrical device corresponds to the both modes of a simplex bus connection mode and a duplex bus connection mode, by collating signals output from two input and output ports for two electrical circuits in an electrical device with a comparator and detecting a fault in the electrical circuits in a duplex bus connection mode, and by checking whether a normal signal is output from an input and output port by collating a signal output from one input and output port for one of the two electrical circuits with the output signal fed back via another input and output port in a simplex bus connection mode.

Description: The present invention relates to an electrical device securing the normality of its output signals, particularly to such a system using the electrical device suitable for composing an input and output terminal or a transmittal terminal of a high reliability system as a fault tolerant system. The first conventional method for constructing a fail safe system is popularly realized by detecting faults in an electrical device or an electrical circuit adapting a self-checking way and realizing continuous operations of the fail safe system by changing the configuration of the system based on the fault detecting results. Examples of such an approach are disclosed in the following references. (1) " A 32-bit Fail Safe MPU Board" by Masayuki Umeyama, Japan Signal Technique Report, Vol. 16, No. 3, pp. 11-16 (1992) (2) " Development of A 32-bit Fail Safe CPU by Noboru Asano, Traffic Electronics and Rail Way Research Committee Report of The Institute of Electrical Engineer of Japan, TER-92-35, pp. 31-41 (1992). The disclosed methods for realizing the fail safe function detect faults in circuits by using a duplicated circuit such as a memory or a micro-processor and collating signals on buses connected to the duplicated circuit. Then, as the second conventional technique, a method feeding back output signals and collating the output signals and signals to be output, is popularly used in order to secure the normality of the output signals. The above-mentioned conventional techniques disclosed in the Japan Signal Technique Report and the Traffic Electronics and Rail Way Research Committee Report of The Institute of Electrical Engineer of Japan, are effectual in the points that those techniques can be easily realized by using general purpose micro-processors or memories. However, the convenience of connection with an outer circuit is not much regarded in the techniques. In the above-mentioned techniques, it is required to use a duplex circuit as a circuit to be connected to a self-checking circuit. However, although such a circuit synchronizing with a processor as a memory can be simply duplicated and dealt with logically as a simplex circuit, such a circuit operating asynchronously with a processor as a transmission interface connected with an outer circuit disturbs the synchronization of a whole system, only by simply duplicating the circuit. Then, as for such a circuit, it is desirable to provide two logically different circuits or devices, but it is not always necessary to connect such a circuit to an outer duplex bus as shown Fig.7. And many of conventional transmission interfaces are designed so as to be connected to a non duplex bus ( hereinafter called simplex bus ) and can not be connected to a duplex bus as shown Fig.7. Then, since error correcting detection of output signals is possible if error correcting codes are added to signals output to a bus, duplication of an outer bus is not always necessary. The conventional output collating method by feeding back output signals is an excellent one for securing the normality of output signals. And, particularly, the said method can detect faults such as disconnection of a wire, a contact failure, etc., as to output signals of a circuit on a wired board, and a fault such as an inferior wire-bonding, an inferior soldering of a pin ( or a lead ), etc., as to a circuit in a semiconductor package. However, in the said method, a counter-measure to increasing of the required points of contact or terminals of pins ( or leads ) is not much regarded yet. Then, the same number of terminals for the feedback as that for output signals is needed for feeding back the output signals. For example, totally 128 terminals are necessary in the method for an address signal of 32 bits and a data signal of 32 bits. Further, if an outer bus is duplicated as mentioned above, totally 256 terminals are necessary. Especially, in such a system, increasing of terminals in a semiconductor device causes increasing of a chip size or a package size which causes in its turn increasing of a failure rate besides weight and volume of a device. Further, since the use of an electrical device having a self-checking function is restricted to a special field and the mass production effects are not large, a cost of a device becomes very high if design and production are individually done for each device for adapting the device to a simplex bus or a duplex bus. EP-A-0287302 discloses an electrical device in which two identical integrated circuit chips (redundant electrical circuits) are connected in parallel to a pair of input/output ports. Each input/output port is connected to a separate simplex bus. In EP-A-0287302, one chip generates output data and the other chip generates a check symbol. The present invention is set forth in the claims. According to a first aspect of the present invention there is provided an electrical device, comprising; a plurality of redundant electrical circuits simultaneously generating the same signals; a plurality of input/output ports connected to external buses, to which at least one of said plurality of redundant electrical circuits is connected; at least one comparison means for collating at least one pair of output signals output by said electrical circuits; and at least one selection means for selecting one of a permission operation and a prohibition operation to outputting an output signal output by at least one of said electrical circuits which is connected to a connection line of one of said input/output ports. According to a second aspect of the present invention it is provided a fault-tolerant system comprising a plurality of electrical devices according to the first aspect, and another selection means arranged to select output of ones of the plurality of electrical devices in which a fault is not detected. The present invention permits an electrical device or a system using the electrical device, to correspond with both buses of a simplex bus and a multiplex bus. The present invention also permits an electrical device to correspond with both buses of a simplex bus and a multiplex bus or a fault tolerant system using the electrical device, capable of securing the normality of output signals without increasing of the terminal number. If the input/output ports are connected to a duplex bus or a multiplex bus, the signals output on the buses are collated and the normality of signals output from the input and output ports are secured by confirming the agreement among the collated signals. Further, if the input/output ports are connected to a simplex bus, the normality of signal output from the input and output part is secured by feeding back an output signal and collating the output signal with the fed back output signal. Furthermore, since another one of the input and output parts connected to a duplex bus, except one of the input and output parts being used to output signals to the bus, is used for the signal feedback, it is possible to feed back the output signals without increasing the number of terminals in the input and output parts. In the drawings: Fig.1 is a diagram showing a fundamental embodiment for the duplex bus connection mode, by the present invention. Fig.2 is a diagram showing a fundamental embodiment for the simplex bus connection mode, by the present invention. Fig.3 shows the constitution of an interface part for the duplex bus connection mode. Fig.4 shows the constitution of an interface part for the simplex bus connection mode. Fig.5 shows an example of a connection way of comparators. Fig.6 shows another example of a connection way of comparators. Fig.7 is a diagram showing the constitution of an example self-checking system to which the embodiment of the present invention is applied. Fig.8 is a diagram showing the constitution of another example self-checking system to which the embodiment of the present invention is applied. Fig.9 is a diagram showing the constitution of an example continuous operation type fault tolerant system to which the embodiment of the present invention is applied. Fig.10 is a diagram showing the constitution of another example continuous operation type fault tolerant system to which the embodiment of the present invention is applied. Hereinafter, embodiments by the present invention are explained referring to drawings. In Figs.1 and 2, the fundamental concept of the present invention is shown. Fig.1 shows an electrical device 10 of an embodiment in accordance with the present invention, which, for example, is connected to two buses 150 and 160 in an outer duplex bus and includes duplicated electrical circuits ( CPU, I/O(input and output terminal), etc. ) 11 and 12. Outputs of the electrical circuits 11 and 12 are connected to the buses 150 and 160 via input and output terminals 15 and 16, respectively. The two outputs of the electrical circuits 11 and 12 are collated by a comparator 14, and the comparator 14 detects a fault occurring in one of the two electrical circuits 11 and 12 as the disagreement between the two outputs and informs the fault occurrence outside. Fig.2 shows an electrical device 10 of an embodiment by the present invention, of which input and output terminals 15 and 16 are connected to a bus 150 in an outer simplex bus, an internal switch of 13 the electrical device 10 being opened in outputting signals to the bus 150 and closed in inputting signals from the bus 150. By the embodiment, the signals output to the bus 150 is fed back via the input and output terminal 16 and collated with the signal to be output at the output of the electrical circuit 11 by the comparator 14. Then, it is secured by the collating results of the comparator 14 that signals are normally output from the input and output terminal 15 to the bus 150. Figs.3 and 4 are diagrams showing composition of an interface part with the outer buses, in the embodiment by the present invention. Fig.3 is a diagram of an example showing the composition in which the electrical device 10 is connected to the buses 150 and 160 of the outer duplex bus and a mode switching signal 166 is set to H level. The output signal 153 of the electrical circuit 11 is output to the bus 150 from a tri-state buffer 151 via the input and output terminal 15. The tri-state buffer 151 is controlled by an input and output control signal 154. The input and output control signal 154 from the electrical circuit 11 is set to H level and the state of the tri-state buffer 151 becomes enable, in outputting signals. In inputting signals, the input and output control signal 154 is set to L level and the state of the tri-state buffer 151 become disable, namely, a high impedance state. Then, the electrical circuit 11 can take in signals on the bus 150 by using a signal line 155 via an input buffer 152. The output signal 163 from the electrical circuit 12 is output from a tri-state buffer 161 to the bus 160 via the input and output terminal 16. The tri-state buffer 161 is controlled by an input and output control signal 164 as explained below. In outputting signals, an output 168 of an AND gate 167 become H level state since the input and output control signal 164 from the electrical circuit 12 is set to H level and a mode switching signal 165 is set to H level, and then the state of the tri-state buffer 161 becomes enable. In inputting signals, the output 168 of the AND gate 167 becomes L level state since the input and output control signal 164 is set to L level, and then the state of the tri-state buffer 161 becomes disable, namely, a high impedance state. Then, the electrical circuit 12 can take in signals on the bus 160 by using a signal line 165 via an input buffer 162. By the embodiment, in outputting signals, the comparator 14 can monitor operations of the electrical circuits 11 and 12 by collating the signals output from the tri-state buffers 152 and 162 via the input buffers 152 and 162. And, in inputting signals, operations of an outside electrical device outputting signals to the buses 150 and 160 can be monitored by collating the signals on the buses 150 and 160. Fig.4 is a diagram showing an example in which the electrical device 10 is connected to an outer simplex bus 150. In the case, the mode switching signal 166 is set to L level. The electrical circuit 11 can transmit signals with the outer simplex bus 150. And the output 168 of the AND gate 167 always becomes a L level state since the mode switching signal 166 is set to L level, and then the state of the tri-state buffer 161 always become disable, namely, a high impedance state. Therefore, the input and output terminal 16 is used exclusively for inputting signals. In outputting signals, signals output from the input and output terminal 15 to the bus 150 appear as the output 165 of the input buffer 162. In inputting signals, signals input to the bus 150 appear as the output 165 of the input buffer 162. Then, the electrical circuit 12 can take in signals on the bus 150 by using a signal line 165 via an input buffer 162. By the embodiment, the comparator 14 can secure that signals from the electrical circuit are normally output to the bus 150, by collating the outputs of the tri-state buffer 151 with the signals output on the bus 150, in outputting signals. And, in inputting signals, operations of an outside electrical device outputting signals to the buses 150 and 160 can be monitored by collating the signals on the buses 150 and 160. In an example shown by Fig.4, only the collation by the feedback of the signal output on the bus 150 in outputting signals is explained for simple explanation. However, it is more desirable to make it possible that operations of the electrical circuits 11 and 12 are monitored besides the collation by the feedback of the signal output on the bus 150, by increasing the number of comparators. Examples of increasing of comparators are shown in Figs.5 and 6. Fig.5 shows an embodiment in which the comparator 14 is inserted between the signal lines 155 and 165, and a comparator 141 between the signal lines 163 and 165. In the duplex bus connection mode by the embodiment, the comparator 14 monitors operations of the electrical circuits 11 and 12 in outputting signals, and operations of an outside electrical device outputting signals to the buses 150 and 160 by collating the signals on the buses 150 and 160 in inputting signals. And, in the simplex bus connection mode, the comparator 14 secure that signals from the electrical circuit are normally output to the bus 150, by collating the outputs of the tri-state buffer 151 with the signals output on the bus 150, and then the comparator 141 monitors operations of the electrical circuits 11 and 12 by collating the signals 165 output on the bus 150 from the electrical circuit 11 with the output signals from the electrical circuit 12, in outputting signals. And the comparator 14 monitors operations of an outside electrical device outputting signals to the buses 150 and 160 by collating the signals on the buses 150 and 160 in inputting signals. Fig.6 shows an embodiment in which the comparator 141 is inserted between the signal lines 153 and 163, and a comparator 14 between the signal lines 155 and 165. In the duplex bus connection mode by the embodiment, the comparators 141 and 14 monitor operations of the electrical circuits 11 and 12 in outputting signals, and operations of an outside electrical device outputting signals to the buses 150 and 160 by collating the signals on the buses 150 and 160 in inputting signals. And, in the simplex bus connection mode, the comparator 14 secure that signals from the electrical circuit are normally output to the bus 150, by collating the outputs of the tri-state buffer 151 with the signals 165 output on the bus 150, and then the comparator 141 monitors operations of the electrical circuits 11 and 12 by collating the signals 153 from the electrical circuit 11 with the output signals 163 from the electrical circuit 12, in outputting signals. And the comparator 14 monitors operations of an outside electrical device outputting signals to the buses 150 and 160 by collating the signals on the buses 150 and 160 in inputting signals. Although there exist other applicable connection ways of comparators besides the examples shown in Figs.3 to 6, such comparators all operate in the same ways as mentioned above. Figs.7 and 8 show examples of self-checking systems using the electrical device 10 of the above-mentioned embodiment by the present invention. If the electrical device 10 of the above-mentioned embodiment is connected to the buses 150 and 160 of an outer duplex bus, the electrical device 10 is used by the duplex bus connection mode, that is, the mode switching signal 166 is set to H level, as shown by Fig.7. In the embodiment, memories 159 and 169 are connected to the buses 150 and 160, respectively, and the both systems operate synchronously. An I/O interface 17 such as a transmittal interface with outside devices is connected to the buses 150 and 160. If the electrical device 10 of the above-mentioned embodiment is connected to a simplex bus 150, the electrical device 10 is used by the simplex bus connection mode, that is, the mode switching signal 166 is set to L level, as shown by Fig.8. Figs.9 and 10 show embodiments of a continuous operation system which is accomplished by developing each of the embodiments shown by Figs.7 and 8. The final output 19 is gained by switching the outputs of the I/O devices shown Figs.7 and 8 by an output selecting mechanism 18. The output selecting mechanism 18 select the signal regarded as normal based on error detecting signals output from the comparators 14 and 141 in the electrical device 10. By the embodiment, a continuous operation system making the most of the feature of securing the normality of output signals from the electrical device 10, can be realized. Furthermore, it is possible to realize a more reliable system by further multiplying the output selecting mechanism. As mentioned above, by the embodiment, it is not necessary to develop individually the electrical device 10 for each of the simplex bus and the duplex bus since the same electrical device 10 can correspond to the both of the simplex bus and the duplex bus, which reduces the development cost, and further the production cost, of the electrical device 10. Then, in the simplex bus connection mode, since another remaining port of the two ports to be used in the duplex bus connection mode is used for feeding back output signals to be checked, the reliability of the electrical device can be increased without increasing the terminal numbers. Especially, in case the electrical device 10 is mounted in a single package, a cheap package having the few number of pins can be used. By the present invention, it is not necessary to develop individually the electrical device 10 for each of the simplex bus and the duplex bus since the same electrical device 10 can correspond to the both of the simplex bus and the duplex bus, which reduces the development cost, and further the production cost, of the electrical device 10. Then, in the simplex bus connection mode, since another remaining port of the two ports to be used in the duplex bus connection mode is used for feeding back output signals to be checked, the reliability of the electrical device can be increased without increasing the terminal numbers. Especially, in case the electrical device 10 is mounted in a single package, a cheap package having the few number of pins can be used.

Claims: An electrical device, comprising; a plurality of redundant electrical circuit (11, 12) simultaneously generating the same signals; a plurality of input/output ports(15, 16) connected to external buses, to which at least one of said plurality of redundant electrical circuits (11, 12)is connected; at least one comparison means (14) for collating at least one pair of output signals output by said electrical circuits (11, 12); and at least one selection means for selecting one of a permission operation and a prohibition operation to outputting an output signal output by at least one of said electrical circuits (11, 12) which is connected to a connection line of one of said input/output ports (15, 16). An electrical device according to claim 1, wherein the total number of said input/output ports (15, 16) is equal to or more than the number of external buses (150, 160) connected to said input/output ports (15, 16) further said at least one selection means selects said permission operation if the total number of said input/output ports (15, 16) equals the number of said external buses (150, 160) and said at least one selection means is arranged to select said prohibition operation to output at least one output signal transmitted to an input/output port (15, 16) which is not connected to an external bus if the total number of said input/output ports is greater than the number of said external buses (150, 160) and, in said prohibition operation said at least one comparison means (14) is arranged to collate said at least one output signal, with at least one of output signal output from said input/output ports (15, 16) which are connected to said external bus (150, 160) by connecting said input/output port (15) outputting said latter at least one output signal and an input/output port (16) which is not connected to an external bus and feeding back said latter at least one output signal via said input/output port (16) not connected to an external bus to said at least one comparison means (14). An electrical device according to claim 2 wherein the total number of said input/output ports (15, 16) is two and each of said two input/output ports (15, 16) are connected to each of two outer buses (150, 160). An electrical device according to claim 1, wherein if said at least one selection means selects said permission operation, said input/output ports (15, 16) are arranged to output the same signal, and if said at least one selection means selects said prohibition operation, said at least one comparison means (14) is arranged to collate a signal output from one of said input/output ports (15, 16) with a signal of which outputting to one of remaining ones of said input/output ports (15, 16) is prohibited by said at least one selection means. An electrical device according to claim 4, wherein said at least one selection means is arranged to select said permission operation when said input and output ports are connected to an outer duplex bus, and said at least one selection means is arranged to select said prohibition operation when said input and output ports are connected to an outer non-duplex bus. An electrical device according to any one of claims 1 to 5, being mounted in one of a single box, a single wiring board, a single chip, a single package and a multi-chip module. An electrical device according to any one of the preceding claims, further including another comparison means (141) for collating a signal output by one of said electrical circuits with a signal received from one of said input/output ports. An electrical device according to any one of claims 1 to 6, further including another comparison means (141) for collating a signal output by one of said electrical circuits with a signal output from another of said electrical circuits. An electrical device according to one of the preceding claims, wherein each said plurality of input/output ports (15, 16) is connected to a respective one of said outer buses, and said selection means selects said permission operation. An electrical device according to one claims 7 to 9, wherein one of said input/output ports (15) is connected to an outer bus, and said selection means selects said prohibition operation, and two of said input/output ports (15, 16) are connected together. A fault tolerant system, comprising: a plurality of electrical devices (10) according to any one of the preceding claims: and another selection means arranged to select outputs of ones of said plurality of said electrical devices in which a fault is not detected. A fault tolerant system according to claim 11, wherein, said selection means is arranged such that, in at least one of said plurality of said electrical device (10), said permission operation is selected when said plurality of input/output ports (15, 16) are connected to an external duplex bus, and said prohibition operation mode is selected when said plurality of input/output ports are connected to a non-duplex bus. A fault tolerant system according to claim 11 or claim 12, wherein at least one of said plurality of said electrical devices (10) is mounted in one of a single box, a single wiring board, a single chip, a single package and a multi-chip module.

Inventors: KANEKAWA NOBUYASU, OHTSUJI SHINYA, SATO YOSHIMICHI, SUZUKI SHOJI, KANEKAWA, NOBUYASU, OHTSUJI, SHINYA, SATO, YOSHIMICHI, SUZUKI, SHOJI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1995
Main classification: G06F11
IPC codes: G06F11