JP3341737B2 - Clock distribution circuit and clock switching system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clock distribution circuit and a clock switching system, and more particularly to a clock switching system for switching a system of a clock signal redundantly configured for each system and a clock distribution circuit suitable for the system.

[0002]

2. Description of the Related Art In general, an apparatus configuration is made redundant as a measure against a failure. In particular, in a device that operates based on a clock signal, if an abnormality occurs in the supplied clock signal, the processing result becomes inaccurate and a fatal state occurs. Therefore, it is very useful to make the clock signal redundant.

As one mode of a clock switching system for switching to one of the redundantly configured clock signals, a clock signal generated by a clock signal generator of each system is input and one of the clock signals is converted to the other clock signal. A clock distribution circuit redundantly configured to select and distribute and mutually perform exclusive control of the active system and the non-operation system, and to distribute comprehensively based on the abnormality detection result detected by each clock distribution circuit And a clock reception selection circuit for selecting a main clock signal from the selected clock signal. That is,
Such a redundantly configured clock distribution circuit is designed to operate as an active system as an active system or as a standby system as a standby system, and the clock distribution circuit of each system is operated or not operated. Depending on which of the systems is operating, the clock selection circuit
A main clock signal is selected from the distributed clock signals. The clock switching system with such a configuration eliminates not only the abnormality that occurred in the transmission path of the clock signal generated for each system, but also eliminates the influence of the failure due to the occurrence of the abnormality at the time of clock switching, and stabilizes the main clock signal. Supply.

FIG. 7 schematically shows the configuration of a conventional clock distribution circuit. In the clock distribution circuit 5, a 0-system clock signal 11 ₀ inputted from the first clock signal input terminal 10 _1, 1-system clock signal 11 ₁ inputted from the second clock signal input terminal 10 ₂ clocks It is input to the selection circuit 12. Clock selection circuit 12
Is in accordance with the clock selection signal 13, and outputs the selected clock signal 14 that selects either one of these 0-system clock signal 11 ₀ and the 1-system clock signal 11 _1. The selected clock signal 14 is supplied to the above-described clock reception selection circuit and also to the clock abnormality detection circuit 15.

System 0 cable disconnection detection signal input terminal 16₀Or
Are the 0-system clock signal 11₀Transmission system
0 cable disconnection detection signal 17 assigned to
And the 0-system cable disconnection detection circuit 18₀Received at. same
Similarly, the 1-system cable disconnection detection signal input terminal 16₁From
1 system clock signal 11₁To the system 1 cable through which
The signed system 1 cable disconnection detection signal 19 is input,
1 system cable break detection circuit 18₁Received at. 0 series
Bull break detection circuit 18₀Is the 0-system cable disconnection detection signal 17
, The disconnection state of the 0-system cable is detected. 1 series
Cable disconnection detection circuit 18 ₁Is the 1-system cable disconnection detection signal 1
9, the disconnection state of the first system cable is detected.

The other system operation state signal 21 indicating the operation state of the other system clock distribution circuit is inputted from the other system operation state signal input terminal 20 and received by the operation / non-operation switching circuit 22. The operation / non-operation switching circuit 22 further receives an operation / non-operation switching control signal 23 and an individual switching control signal 24. The individual switching control signal 24 is obtained by removing noise in the noise removing circuit 27 from the individual control switching control signal 26 input from the individual control signal input terminal 25. The operation / non-operation switching circuit 22 determines the operation state of the own system from the other system operation state signal 21, the operation / non-operation switching control signal 23, and the individual switching control signal 24. The determined operation state of the own system is notified as a self-system operation state signal 28 from a self-system operation state signal output terminal 29 to a redundantly configured clock distribution circuit of another system (not shown), and mutual exclusive control is performed. Will be

[0007] The self-failure detection circuit 30 detects the occurrence of a failure inside the clock distribution unit 5.

When an abnormality of the selected clock signal 14 is detected by the clock abnormality detection circuit 15, a control bus interface (Interfac
e: Hereinafter, abbreviated as IF. ) 32. The control bus IF 32 is connected to a control unit (not shown) via the control bus 33. The control bus IF 32 notifies a control unit (not shown) via the control bus 33 of the occurrence of an abnormality due to the clock abnormality detection signal 31. When notified, the control section sends a clock switching instruction signal via the control bus 33 to the clock selection circuit 12 for selectively outputting the selected clock signal 14 to switch to the other system clock signal. . The control bus IF 32 receives this clock switching instruction signal and outputs it to the clock selection circuit 12 as the clock selection signal 13.

A system 0 or system 1 cable disconnection detection circuit 18
_0, 18 when the ₁ by the cross-sectional state of the 0-system or 1-system cable is detected, it is input to the control bus IF32 as each 0 system or 1-system disconnection occurrence detection signal 34 _0, 34 _1.
The control bus IF 32 notifies a control unit (not shown) via the control bus 33 that an abnormality has occurred due to the 0-system or 1-system disconnection detection signals 34 ₀ and 34 ₁ . When notified, the control unit 33 sends a clock switching instruction signal, which instructs the clock selection circuit 12 that selects and outputs the selected clock signal 14 not to select the clock signal of the system in which the cable is disconnected, to the control bus 33. And a switching control signal for selecting the clock signal of the system in which the cable break has been detected by the clock selection circuit and instructing the clock distribution circuit operating as the active system to become the non-active system through the control bus 33. To send out. Further, similarly, an individual control switching control signal for instructing a non-operating system is transmitted via an individually controlled individual control signal line. In the individual control signal line, the control bus 33 is also connected to other functional units,
This is a remedy for avoiding a situation in which the switching control of the clock system becomes impossible due to a failure occurring in another functional unit, and the system switching control is configured in a duplicated manner. Such an individual control signal line is connected to the individual control signal input terminal 25.

Therefore, in the control bus IF 32, the clock switching instruction signal from the control unit is sent to the clock selection signal 13
And outputs a switching control signal to the operation / non-operation switching circuit 22 as an operation / non-operation switching control signal 23. The individual control switching control signal 26 input from the individual control signal input terminal 25 has its noise removed by a noise removing circuit 27, and is input to the active / inactive switching circuit 22 as an individual switching control signal 24. In the noise elimination circuit 27, since the individual control signal lines are individually wired to each part of the system for use for the above-described purpose, the wiring density of the signal lines increases, and noise is likely to occur due to interference with each other. ,
This is to remove this.

When the self-failure detection circuit 30 detects the occurrence of a failure inside the clock distribution unit 5, it is input as a self-failure detection signal 35 to the control bus 32 and below. The occurrence of a failure by the self-failure detection signal 35 is notified to a control unit (not shown) via the control bus 33. When notified, the control unit sends, via the control bus 33, a switching control signal for instructing the clock distribution circuit that has detected the occurrence of the failure to be in a non-operating state. Further, similarly, an individual control switching control signal for instructing a non-operating system is transmitted via an individually controlled individual control signal line. Therefore, the control bus IF 32 outputs the switching control signal from the control unit to the operation / non-operation switching circuit 22 as the operation / non-operation switching control signal 23. Also, an individual control switching control signal 26 input from the individual control signal input terminal 25
The noise is removed by the noise removal circuit 27 and is input to the operation / non-operation switching circuit 22 as the individual switching control signal 24.

The operation / non-operation switching circuit 22 performs system switching according to the following transition diagram.

FIG. 8 shows an outline of system switching control in the operation / non-operation switching circuit 22 of the clock distribution circuit 5. Here, the other system operation state signal 2 indicating the operation state of the clock distribution circuit of the other system corresponding to its own operation / non-operation state (initial) 40 indicating the operation state before the system switching control.
1, the presence / absence 42 of the operation / non-operation switching control signal 23 from the control bus IF 32, the state transition 43 indicating whether or not to perform the system switching control, and the own operation / non-operation of the result of the state transition. A state (after control) 44 and a state 45 of an ACT lamp (not shown) that is turned on during the operation state are shown. For example, in the first stage, before the system switching control, the other system input from the other system clock distribution circuit via the other system operation state signal input terminal 20 to the own system clock distribution circuit which was the active system. When it is notified by the operation state signal 21 that "the transition from the non-working system to the working system" has been made, and when the operation / non-operation switching control signal 23 is input from the control bus IF 32, it means that the switching control is performed. . As a result, the clock distribution circuit of the own system becomes a non-operating system, and the ACT lamp is turned off. Further, for example, in the fifth stage, before the system switching control, a signal is input from the other system clock distribution circuit to the own system clock distribution circuit via the other system operation state signal input terminal 20 to the non-working system clock distribution circuit. The other system operation status signal 21 indicates that "transition from the operation system to the non-operation system" has occurred, and the control bus I
When the operation / non-operation switching control signal 23 is input from F32, this means that the previous value is held without performing the switching control. As a result, the clock distribution circuit of the own system remains in the non-operating system, and the ACT lamp remains off. Here, if it is determined that the system switching control is disabled by the control bus 33 for some reason, the presence / absence 42 of the operation / non-operation switching control signal 23 from the control bus IF 32 is input from the individual control signal input / output terminal 25. Individual switching control signal 2
In place of the process No. 4, a determination is similarly made as to whether or not to perform system switching control.

As described above, in the clock distribution circuit, the system switching control signal from the control unit is received not only through the control bus but also through the individual control signal line, whereby the abnormality of the clock signal of each system and the clock distribution circuit itself Appropriate clock signal distribution is realized even when an abnormality or a cable disconnection in each system occurs.

As a technique related to such a clock distribution circuit, Japanese Unexamined Patent Application Publication No. 7-64666, entitled "Method of Preventing Device Malfunction When Clock Disturbs", selects a control unit based on various abnormalities detected by the clock distribution circuit. When switching the system, in order to prevent the occurrence of secondary abnormality detection due to clock disturbance occurring when the selected clock is cut off due to the switching, a mask pulse is provided to the control unit when an abnormality is detected in each system, and A technique for masking detection of a detected secondary abnormality is disclosed.

[0016]

As described above, FIG.
Has a cable disconnection detection circuit corresponding to each of the 0-system and 1-system cables. For example, when a cable is disconnected, a disconnection occurrence detection signal is generated, and a control unit (not shown) Alarm will be sent out. In response to this, the control unit responds to the control bus 3
3. The operation / non-operation switching circuit 22 is controlled by the operation / non-operation switching control signal 23 via the control bus IF 32 and the switching control signal 24 via the individual control signal line so as to become the non-operation system. I do. In this case, since the control bus 33 is also connected to other functional units, there is no problem when these other functional units are operating normally, but a failure occurs in the other functional units and the control bus 33 When the system switching control by the transmitted control signal becomes impossible, the system switching control via the control bus 33 cannot be performed. Therefore, system switching control is performed according to the switching control signal 24 via the individual control signal line.

By the way, in order to improve the reliability, the individual control signal lines are individually wired to each part of the whole system, so that the number of the individual control signal lines becomes enormous, and the electric signals of the signals transmitted by interfering with each other are transmitted. The levels become unbalanced, and noise is likely to be added. Therefore, a noise removing circuit 27 is provided as shown in FIG. 7 to remove the added noise.

Normally, when a cable is disconnected, a cable disconnection state is detected in the clock distribution circuits of the 0-system and the 1-system, but system switching is not performed as long as the switching control shown in FIG. 8 is followed. However, the situation in which the cable is actually disconnected is caused by the 0-system and 1-system cable disconnection detection signals 1
Reference numerals 7 and 19 denote transient changes, which are clock distribution circuits for the 0-system and the 1-system, and the manner in which noise is removed by the noise removal circuit 27 may be slightly different. As a result, the switching control of the working clock distribution circuit to the non-working state may be performed first, and the system in which the cable is disconnected is the working system, and the system in which the cable is normally connected is the system. There is a problem that system switching is executed as a protection system.

In such a situation, Japanese Patent Application Laid-Open No. 7-64666
By applying the technique disclosed in Japanese Patent Laid-Open No. H10-209, there is a possibility that the above-mentioned problem can be solved. However, it is necessary to wire the mask pulse to a control unit (not shown), and since the individual control signal lines are enormous as described above, noise may be added to the mask pulse and the cable may be disconnected. It is not possible to accurately mask transient changes, and the reliability is rather reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a clock distribution circuit and a clock distribution circuit capable of normally controlling system switching even when an abnormality accompanied by a transient change such as disconnection of a cable supplied with a clock signal is detected. It is to provide a clock switching system to which this is applied.

[0021]

According to the first aspect of the present invention, (a) clock selecting means for selecting and distributing one of the redundantly configured 0-system and 1-system clock signals, and (b) Disconnection state detection means for detecting the disconnection state of the transmission line for supplying the clock signals of the 0 system and 1 system for each of the redundantly configured systems; and (c) disconnection state detection means for any one of the transmission lines of the system. A disconnection state occurrence alarm notification means for notifying a disconnection state occurrence alarm via a predetermined control bus when the disconnection state is detected; and (d) an individual control signal line provided separately from the predetermined control bus. A first system switching instruction signal for instructing system switching is received in response to the disconnection state occurrence alarm notified by the disconnection state occurrence alarm notification unit, and a noise component added to the first system switching instruction signal is removed. Output as individual switching control signal The noise selecting means is selected by the clock selecting means based on the noise switching means and the clock switching instruction signal received in response to the disconnection state occurrence alarm notified by the disconnection state occurrence alarm notification means via the predetermined control bus. Clock selection control means for switching the clock signal to the other system; and (f) a first system received in response to the disconnection state alarm notified by the disconnection state alarm notification means via a predetermined control bus. Operation state switching means for switching the operation state of the own system based on the second system switching instruction signal for instructing the system switching similarly to the switching instruction signal, the individual switching control signal, and the operation state of the other system that is exclusively controlled. And (g) suppression means for suppressing the system switching control of the operation state switching means by the individual switching control signal when the disconnection state of any one of the transmission lines is detected by the disconnection state detecting means. It is provided to a clock distribution circuit.

In other words, according to the first aspect of the present invention, a clock signal selectively selected from the 0-system and 1-system clock signals redundantly configured by the clock selecting means is distributed, and is mutually exclusive with another system by the redundant configuration. In the controlled clock distribution circuit, a disconnection state of a transmission line for supplying a clock signal of each system is detected, and this is notified as a disconnection state occurrence alarm on a predetermined control bus. When the first system switching signal is received via an individual control signal line provided separately from the control bus in response to the disconnection state alarm, the noise removal means causes a huge number of signals to be transmitted between adjacent signal lines. An individual switching control signal is generated in which noise of the first system switching instruction signal via the individual control signal line added due to mutual interference or the like is removed. Then, based on the second system switching instruction signal received via the control bus in response to the individual switching control signal and the disconnection state occurrence alarm and the operation state of the other system, system operation switching is performed by the operation state switching means. At this time, even if the system switching control needs to be performed by the individual switching control signal, such as when the system switching control is disabled based on the second system switching instruction signal for some reason or the like, the disconnection is performed. When the disconnection state of the transmission line is detected by the state detecting means, the system switching control by the individual switching control signal is suppressed.

According to a second aspect of the present invention, in the clock distribution circuit of the first aspect, the clock abnormality detecting means for detecting an abnormality of the clock signal selected by the clock selecting means, and the clock signal is selected by the clock abnormality detecting means. Clock abnormality occurrence alarm notifying means for notifying a clock abnormality occurrence alarm via a predetermined control bus when an abnormality of the clock signal is detected, wherein the clock selection control means includes a clock abnormality generation alarm via the predetermined control bus. The clock signal selected by the clock selection means is switched to the other system based on the clock switching instruction signal received in response to the clock abnormality occurrence alarm notified by the notification means.

That is, according to the second aspect of the present invention,
An abnormality of the clock signal itself to be selectively distributed is detected, and when the abnormality is detected, a clock abnormality occurrence alarm is issued via the control bus. When a clock switching instruction signal is received correspondingly, the clock signal system selected by the clock selection control means is switched to the other system.

According to a third aspect of the present invention, in the clock distribution circuit of the second aspect, a failure detecting means for detecting occurrence of an internal failure and a predetermined control bus when the occurrence of the failure is detected by the failure detecting means. A failure occurrence alarm notifying unit for notifying a failure occurrence alarm via the control unit, and the noise removing unit is configured to instruct the system switching in response to the failure occurrence alarm notified by the failure occurrence alarm notification unit via the individual control signal line. 3
The system switching instruction signal is received, the noise component added to the third system switching instruction signal is removed, the signal is output as an individual switching control signal, and the operation state switching means is provided with a failure occurrence alarm via a predetermined control bus. When the fourth system switching instruction signal for instructing system switching is received in the same manner as the third system switching instruction signal in response to the failure occurrence alarm notified by the notifying unit, the system switches to the non-working system. It is characterized by.

That is, according to the third aspect of the present invention, the inside of the clock distribution circuit itself is detected, and when an abnormality is detected, a failure occurrence alarm is issued via the control bus. Then, when the third system switching signal is received via an individual control signal line provided separately from the control bus, a large number of adjacent signal lines are mutually connected by the noise removing means. An individual switching control signal is generated by removing noise of the first system switching instruction signal via the individual control signal line added due to interference or the like. Then, based on the fourth system switching instruction signal received via the control bus in response to the individual switching control signal and the failure occurrence alarm and the operating state of the other system, the system switching is performed by the operating state switching means.

According to the fourth aspect of the present invention, (a) a 0-system and 1-system clock transmitting means for transmitting redundant 0-system and 1-system clock signals, and (b) a 0-system and 1-system clock signal, respectively. 0 system for supplying and 0 system and 1 system transmission lines for transmission, and (c) 0 system and 1 system
Clock selecting means for selecting and distributing any one of the clock signals transmitted by the system clock transmitting means,
A disconnection state detecting means for detecting a disconnection state of a transmission line for supplying a clock signal for each system, and a predetermined control bus when a disconnection state of any transmission line of the system is detected by the disconnection state detection means. Corresponding to the disconnection state occurrence alarm notified by the disconnection state occurrence alarm notification means via an individual control signal line provided separately from a predetermined control bus. Noise removing means for receiving a first system switching instruction signal for instructing system switching, removing a noise component added to the first system switching instruction signal, and outputting the signal as an individual switching control signal; The clock signal selected by the clock selection means based on the clock switching instruction signal received in response to the disconnection state generation alarm notified by the disconnection state generation alarm notification means via Clock selection control means for switching to the first state, and system switching similar to the first system switching instruction signal received in response to the disconnection state occurrence alarm notified by the disconnection state occurrence alarm notification means via a predetermined control bus. An operation state switching unit that switches the operation state of the own system based on the second system switching instruction signal to be instructed, the individual switching control signal, and the operation state of the other system that is exclusively controlled; (A) a redundant system comprising a system 0 and system 1 clock distribution circuit, comprising: a system switching control unit for suppressing system switching control of an operation state switching unit by an individual switching control signal when a disconnection state of the transmission line is detected. A) a second system switching instruction signal and a clock switching instruction signal and a separate control signal line via a predetermined control bus based on a disconnection state occurrence alarm notified from the 0-system and 1-system clock distribution circuits. System switching control means for transmitting the first system switching instruction signal to the first system switching instruction signal, and (e) operation of the clock distribution circuit of each system among the clock signals selected by the clock selection means of the 0 system and 1 system clock distribution circuits. The clock switching system is provided with clock reception selecting means for generating a main clock signal that is alternatively selected according to the state.

That is, according to the fourth aspect of the present invention, the clock distribution circuit of the first aspect of the present invention, which is redundantly configured and mutually exclusively controlled, is provided for each system by the clock transmitting means having the redundant configuration. The clock signals of the 0-system and the 1-system are transmitted via the transmission path. The clock signal selected and distributed by the clock distribution circuit of each system is selectively selected by a clock reception selecting means according to the operation state of the clock distribution circuit of each system to generate a main clock signal. ing.

According to a fifth aspect of the present invention, in the clock switching system according to the fourth aspect, each of the 0-system and 1-system clock distribution circuits detects an abnormality of the clock signal selected by the clock selecting means. Means, and clock abnormality occurrence alarm notification means for notifying a clock abnormality occurrence alarm via a predetermined control bus when an abnormality of the clock signal selected by the clock abnormality detection means is detected, and the clock selection control means A clock signal selected by the clock selection means based on the clock switching instruction signal received in response to the clock abnormality occurrence alarm notified by the clock abnormality occurrence alarm notification means via the predetermined control bus to the other system. The system switching control means is notified from the 0-system and 1-system clock distribution circuits. Is characterized in that on the basis of the lock abnormality alarm is to transmit the clock switching instruction signal via a predetermined control bus.

That is, according to the fifth aspect of the present invention, the clock distribution circuit of each of the redundantly configured systems further detects an abnormality in the clock signal itself to be selectively distributed, and when the abnormality is detected, connects the control bus. A clock abnormality occurrence alarm is issued via the CPU. When a clock switching instruction signal is received correspondingly, the clock signal system selected by the clock selection control means is switched to the other system.

According to a sixth aspect of the present invention, in the clock switching system according to the fifth aspect, the clock distribution circuits of the 0-system and the 1-system are each provided with fault detecting means for detecting occurrence of an internal fault, and the fault detecting means. A failure occurrence alarm notifying unit for notifying a failure occurrence alarm via a predetermined control bus when the occurrence of a failure is detected, wherein the noise removing unit includes a failure notified by the failure occurrence alarm notifying unit via an individual control signal line. A third system switching instruction signal for instructing system switching in response to the occurrence alarm is received, a noise component added to the third system switching instruction signal is removed, and the signal is output as an individual switching control signal. The switching unit performs system switching in the same manner as the third system switching instruction signal received in response to the failure occurrence alarm notified by the failure occurrence alarm notification unit via the predetermined control bus. It is characterized in that when the fourth system switching instruction signal Shimesuru is received is to switch to a non-active.

That is, in the invention according to the sixth aspect, the clock distribution circuits of the respective redundantly configured systems further detect the inside of the clock distribution circuit itself, and when the abnormality is detected, the failure is detected via the control bus. Issue an occurrence alarm.
Then, when the third system switching signal is received via an individual control signal line provided separately from the control bus, a large number of adjacent signal lines are mutually connected by the noise removing means. An individual switching control signal is generated by removing noise of the first system switching instruction signal via the individual control signal line added due to interference or the like. Then, based on the fourth system switching instruction signal received via the control bus in response to the individual switching control signal and the failure occurrence alarm and the operating state of the other system, the system switching is performed by the operating state switching means.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 schematically shows the configuration of a clock switching system to which a clock distribution circuit according to an embodiment of the present invention is applied. However, the same portions as those of the clock distribution circuit shown in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. The clock switching system includes a basic unit 5 for generating redundantly configured 0-system and 1-system clock signals.
0, and an additional unit 51 for selecting an operating system clock signal from each system clock signal generated by the basic unit 50. The 0 system clock signal is a 0 system cable 52 ₀ , and the 1 system clock signal is a 1 system clock signal. It is connected via the cable 52 _1. The basic unit 50, the 0-system clock signal and 0-system clock transmission portion 53 ₀ that transmits the generated 0-system clock signal via the 0-system cable 52 ₀ to an expansion unit 51 and the product was 1-based cable 1 system clock signal and a 1-system and the clock transmission section 53 ₁ for transmitting the 1-system clock signal to the expansion unit 51 through the 52 _1.

The extension unit 51 receives the 0-system and 1-system clock signals transmitted by the 0-system and 1-system clock transmission units 53 ₀ and 53 ₁ via the 0-system and 1-system cables 52 ₀ and 52 ₁ , respectively. Redundantly configured 0-system and 1-system clock distribution unit 54 for distributing either one to each unit in the extension unit
₀ , 54 ₁ , a clock reception selection unit 55 for selecting one of the clock signals respectively distributed by the clock distribution units of each system, and a system of redundantly configured 0 system and 1 system clock distribution units 54 ₀ , 54 ₁ A control unit 56 for performing switching control.

System 0 clock distribution unit 54₀Is the 0 series and
1 system cable 52₀, 52₁Through system 0 and system 1
Transmission unit 53₀, 53₁System 0 sent by
1 system clock signal 57₀, 57₁Is entered. Further
The 0-system clock distribution unit 54 ₀Has a system 0 cable 52₀
0 cable disconnection detection signal line 58 assigned to₀And
And system 1 cable 52₁System cable assigned to
Disconnection detection signal line 58₁Are connected respectively. 1 system
Clock distribution unit 54₁Similarly, 0 series and 1 series cables
Le 52₀, 52₁0 and 1 system clock transmission unit via
53₀, 53₁System 0 and system 1 transmitted by
Signal 57₀, 57₁Is entered. In addition,
Lock distribution unit 54₁Also, 0 series cable 52₀Assign to
0 cable disconnection detection signal line 58₀And 1 series cave
Le 52₁1 cable disconnection detection signal line 5 assigned to
8₁Are connected respectively.

In the extension unit 51, the 0-system and 1-system clock distribution units 54 ₀ and 54 ₁ and the control unit 56 are connected via the control bus 33, and the 0-system and 1-system clock distribution units 54 _{0 and} 54 _{0 are connected.} transmission and reception of the clock switching instruction signal and a system switching instruction signal for which is the various alarms and which issued in 54 ₁ is performed. Further, individual control signal lines are individually wired between the control unit 56 and the 0-system and 1-system clock distribution units 54 ₀ and 54 _1.
System clock distributor 54 ₀ relative to the 0-system individual control for switching control signal 59 _0, 1 system clock distributor 54 ₁ per system individually controlling the switching control signal 59 ₁ is transmitted. The 0-system and 1-system clock distribution units 54 ₀ and 54 ₁ mutually transmit and receive own system operation state signals 60 ₀ and 60 ₁ indicating the operation state of the own system. The self-system operation state signals 60 ₀ and 60 ₁ are also supplied to the clock reception selection unit 55. 0-system and 1-system clock distributor 54 _0, 54 from _1, alternatively selected 0-system and 1-system selection clock signal 61 ₀ for each system from the 0-system and 1-system clock signal 57 _0, 57 ₁ , 61 ₁ is supplied to the clock reception selecting section 55.

The clock reception selection unit 55 includes a system 0 and a system 1
_{One of} the 0-system and 1-system selection clock signals 61 ₀ , 61 ₁ is selected according to the own system operation state signals 60 ₀ , 60 ₁ from the system clock distribution units 54 ₀ , 54 ₁ , and the main clock signal is selected. Generate

In the clock switching system having such a configuration, _one of the system clock signals input by each of the 0-system and 1-system clock distribution units 54 ₀ and 54 ₁ which are mutually exclusive controlled is selected, and the system is switched. Of the selected clock signal, a failure of the clock distribution unit itself, a redundant system 0 and 1
The disconnection state of the system cable can be detected and the control unit 56 can be notified as an alarm via the control bus 33.

In response to the alarm, the control unit 56 switches the clock selection and the system operation to the clock distribution units 54 ₀ and 54 _{1 of} each system via the control bus 33 and the individual control signal lines. For transmitting the instruction signal. The clock distribution unit of each system normally performs system switching control or the like in accordance with a switching control signal via the control bus 33. However, when a failure occurs in another functional unit to which the control bus 33 is connected, the system When the switching control is disabled, the system switching control is performed in accordance with the individual control switching control signal received via the individual control signal line. Since the individual control signal line for transmitting the switching control signal for individual control is individually wired to each functional unit of the system, the number of the individual control signal lines becomes enormous, and considering that noise is added, Noise is removed once in each clock distribution unit.

In the clock distribution unit in this embodiment, when the disconnection of the cable is detected, the individual switching control signal from which the noise has been removed as described above is masked so that the system switching control is not performed by the individual switching control signal. In this way, a normal clock signal can be supplied to the system even when system switching control via the control bus is not possible and a transient change such as disconnection of the cable to which the clock signal is supplied is detected. And improve the reliability of the system.

Hereinafter, the main part of the clock switching system shown in FIG. 1 will be described.

[0044] Figure 2 illustrates a construction main part of the 0-system clock distributor 54 ₀ in this embodiment. Here is a description of the 0-system clock distributor 54 _0, 1
System clock distributor 54 ₁ is the same. In the 0-system clock distributor 54 _0, 1 system clock signal is input 0-system clock signal 57 ₀ inputted from the first clock signal input terminal 70 _1, the second clock signal input terminal 70 ₂ 5
7 ₁ and is inputted to the clock selection circuit 71. The clock selection circuit 71 operates according to the clock selection signal 72.
Alternatively it outputs the 0-system selection clock signal 61 ₀ selected 0-system clock signal 57 ₀ from among the 1-system clock signal 57 _1. 0 system selected clock signal 61 _0, together are distributed to clock reception selection unit 55 is also input to the clock abnormality detection circuit 73.

System 0 cable disconnection detection signal input terminal 74
₀Is the 0-system cable disconnection detection signal line 58₀Is connected
You. Similarly, the 1-system cable disconnection detection signal input terminal 74
₁Is the 1-system cable disconnection detection signal line 58₁Is connected
You. 0 system and 1 system disconnection detection signal line 58₀, 58₁Is the basic
0-system and 1-system clock transmission unit 53 of unit 50₀, 53₁When
0-system and 1-system clock distribution unit 54 of extension unit 51₀, 5
4₁Connected to a common GND between
0-system and 1-system cable disconnection detection circuit connected to these
75 ₀, 75₁Has been pulled up. Cable of each system
The disconnection detection circuit outputs the 0-system and 1-system cable disconnection signals respectively.
Line 58₀, 58₁By monitoring the signal level of
The disconnection state of each cable can be detected. Sand
That is, when the monitored signal level is a logical level "L",
Always judge that the cable is connected, and
When the bell is at the logic level "H", the common GND is disconnected.
It is determined that the cable is disconnected.

Via the other system operation state signal input terminal 76,
1 system own system operational status signals 60 ₁ of the clock distribution unit 54 ₁ of 1 system showing an operation state of the clock distributor ₅₄₁ is input,
It is received by the operation / non-operation switching circuit 77. The operation / non-operation switching circuit 77 further includes an operation / non-operation switching control signal 7.
8 and the suppression switching control signal 79 are input. Inhibit switching control signal 79, to the individual control signal input terminal 80 individually control the switching control signal 59 ₀ input from, after the noise has been removed in the noise removing circuit 81, is output through further suppression circuit 82 Things. Operation / non-operation switching circuit 77
Is the system 1 operation status signal 60 ₁ ,
The operation state of the own system is determined from the non-operation switching control signal 78 and the suppression switching control signal 79. Operational state of the determined 0 system clock distributor 54 ₀ own system operation state signal 6
0 ₀ As output from the self-system operation state signal output terminal 83 for one system clock distributor 54 _1, and is exclusive control each other.

[0047] Self-fault detection circuit 84 detects a clock distributor 54 ₀ internal failure.

[0048] When the abnormality of the clock abnormality detection circuit 73 by the 0-system selection clock signal 61 ₀ is detected, it is input to the control bus IF86 as the clock abnormality detection signal 85. The clock abnormality detection circuit 73 receives, for example, 0
Detecting a rising edge of the system selected clock signal 61 _0, the mono-multi integrated circuit for stretching the logical level "H" for a predetermined time, stretching the one period of the 0-system selection clock signal 61 _0, the logic level "H" If the logic level is "L", it is determined that an abnormality has occurred, and abnormality detection is performed.

The control bus IF 86 is connected to the control unit 56 via the control bus 33. Control bus IF86
The control bus 33 detects the occurrence of an abnormality based on the clock abnormality detection signal 85 output by the clock abnormality detection circuit 73.
Is notified to the control unit 56 via. In the control unit 56, when it is notified, the 0-system selection clock signal 61 ₀ relative to the clock selection circuit 71 selectively outputs the clock switching instruction signal to the control bus 33 that instructs to switch the clock signal of the other system Via Control bus IF86
Then, this clock switching instruction signal is received and output to the clock selection circuit 71 as the clock selection signal 72.

0-system and 1-system cable disconnection detection circuit 7
When the disconnection state of the 0-system or 1-system cable is detected by 5 ₀ and 75 ₁ , respectively, it is input to the control bus IF 86 and the suppression circuit 82 as the 0-system or 1-system disconnection occurrence detection signals 87 ₀ and 87 ₁ . When the suppression circuit 82 is notified that one of the 0-system or 1-system disconnection occurrence detection signals 87 ₀ and 87 ₁ has detected the cable disconnection state, the noise removal circuit 81 controls the individual control switching control signal 59.
Mask the output signal from which ₀ noise has been removed. That is, so as not performed the system switching by individual control for switching control signal 59 _0. System 0 or system 1 disconnection detection signal 8
7 _0, the 87 _1, both cable with when the cable disconnection state is notified that they are not detected, it is operational and non-operational switching circuit 77 to the noise of the individual control for the switching control signal 59 ₀ by the noise elimination circuit 81 Is supplied to the operation / non-operation switching circuit 77 as the suppression switching control signal 79.

Further, the control bus IF 86 notifies the control unit 56 via the control bus 33 of the occurrence of the disconnection state due to the 0-system or 1-system disconnection detection signals 87 ₀ and 87 ₁ . In the control unit 56, when it is notified, the 0-system selection clock signal 61 ₀ clock switching instruction signal instructing not to select the clock signal of the system became cable disconnection state to the clock selection circuit 71 that selectively outputs Via the control bus 33, and also selects a clock signal of the system in which the cable disconnection is detected by the clock selection circuit and instructs the clock distribution circuit operating as the active system to switch to the non-active system. It is sent out via the control bus 33.
Further, similarly, an individual control switching control signal for instructing a non-operating system is transmitted via an individually controlled individual control signal line. The individual control signal line is a rescue circuit for avoiding a situation in which the control bus 33 is also connected to other functional units and a clock system switching control cannot be disabled due to a failure occurring in the other functional units. System switching control is duplicated. Such an individual control signal line is connected to the individual control signal input terminal 80.

Therefore, the control bus IF 86 outputs the clock switching instruction signal from the control unit 56 to the clock selection circuit 71 as the clock selection signal 72, and the switching control signal as the operation / non-operation switching control signal 78. Output to the operation / non-operation switching circuit 77. Further, individual control signal input terminal 80 individually control the switching control signal 59 ₀ inputted from the input to the noise eliminating circuit 81 as described above. In the noise elimination circuit 81, since the individual control signal lines are individually wired to respective parts of the system for use for the above-described purpose, the wiring density of the signal lines increases, and noise is likely to occur due to interference with each other. , To remove this.

[0053] When the self-fault detecting circuit 84 abnormal internal ₀ clock distributor 54 by is detected, it is input to the control bus IF86 as a self-failure detection signal 88. The control bus IF 86 notifies the control unit 56 via the control bus 33 that a failure has occurred due to the self-failure detection signal 88. When notified, the control unit 56 sends a switching instruction signal via the control bus 33 to instruct the clock distribution circuit that has detected the failure to operate as a non-operating system. Further, similarly, an individual control switching control signal for instructing a non-operating system is transmitted via an individually controlled individual control signal line. Therefore, the control bus IF 86 outputs the switching instruction signal from the control unit 56 to the operation / non-operation switching circuit 77 as the operation / non-operation switching control signal 78. Further, individual control for switching control signal 59 ₀ input from the individual control signal input terminal 80 is input to the noise removing circuit 82.

The operation / non-operation switching circuit 77 performs system switching control according to the switching conditions shown in FIG.

FIG. 3 shows the main components of the control unit 56 shown in FIG. The control unit 56 is a central processing unit (Central Processing Unit: hereinafter abbreviated as CPU).
90 and an individual control signal output circuit 91. C
When the PU 90 is notified from the clock distribution units of the respective systems via the control bus 33 as alarms that a clock signal has been abnormally detected, that the cable has been disconnected, or that the clock distribution unit itself has failed, the PU 90 responds to the content of the notified alarm. The system switching control is performed via the control bus 33 and the individual control signal lines. In order to perform the switching control via the individual control signal line, the CPU 90 designates the control destination and the switching control content for the individual control output circuit 91 and causes the individual control signal output circuit 91 to decode. The individual control signal output circuit 91 outputs the decoded result as an individual control switching control signal 92 via the individually controlled individual control signal lines to the 0-system and 1-system clock distribution units 54 ₀ , 54 _1, etc. Output to the function unit.

The control unit 56 has a predetermined storage device for storing the above-described control program.
U90 can execute the switching control according to the control program.

FIG. 4 shows an outline of the processing contents of the switching control of the CPU 90. First, the CPU 90 determines whether or not abnormality of the selected clock signal of each system notified by the clock abnormality detection signal from the clock distribution unit of each system via the control bus 33 (step S1).
00). Here, when it is determined that the abnormality of the selected clock signal of each system is detected (step S100: Y), the clock distribution unit of the system in which the clock abnormality is detected is
A clock switching instruction signal for instructing to switch the clock selection circuit of the clock distribution unit to the other system is transmitted via the control bus 33 (step S101), and a series of processing ends (end).

In step S100, when it is determined that no abnormality is detected in the selected clock signal of each system (step S100: N), notification is made by a self-failure detection signal from the clock distribution unit of each system via the control bus 33. It is determined whether or not the failure of the clock distribution unit itself is detected (step S102). Here, when it is determined that a failure of the clock distribution unit itself has been detected (step S10).
2: Y), a switching instruction signal for instructing the clock distribution unit of the system in which the failure of the clock distribution unit is detected to switch to the non-operational system by the operation / non-operation switching circuit of the clock distribution unit. 33, an individual control signal output circuit 91 outputs a similarly detected system and an individual switching instruction for instructing to switch this system to a protection system.
To output a switching control signal for individual control via the corresponding individual control signal line (step S103), and a series of processing ends (end).

If it is determined in step S102 that a failure has not been detected in the clock distribution unit itself of each system (step S102: N), the 0 or 1 system disconnection of the clock distribution unit of each system is performed via the control bus 33. It is determined whether or not the disconnection state of the cable of each system notified by the occurrence detection signal has been detected (step S104). Here, when it is determined that the disconnected state of the cable is detected (step S10).
4: Y) First, a clock switching instruction signal for instructing the clock distribution unit of each system to select a clock signal of a system in which a cable disconnection state is not detected is transmitted via the control bus 33 (Step S105). ). Furthermore, a switching instruction for selecting the system in which the stage state of the cable is detected by the clock selection circuit and instructing the clock distribution unit which is the operating system to switch to the non-operation state by the operation / non-operation switching circuit. The individual control signal output circuit 91 transmits a signal via the control bus 33 and similarly issues an individual switching instruction for switching between the system to be controlled and the protection system.
To output a switching control signal for individual control via the corresponding individual control signal line (step S106), and a series of processes is ended (END).

FIG. 5 shows a main part of the configuration of the clock reception selecting section 55 shown in FIG. The clock reception selection unit 55 includes a two-input one selector 110 and a switching control unit 1
11 is provided. 2 Input 1 selector 111, the 0-system clock distributor 54 0 system selected clock signal 61 ₀ outputted from _0, from the 1-system clock distributor 54 1 system selected output from ₁ clock signal 61 _1, switching Control unit 11
Either one is output as the main clock signal 113 in accordance with the selected clock switching signal 112 output by 1.

The switching control section 111 receives the own-system operation state signals 61 ₀ and 61 ₁ from the 0-system and 1-system clock distribution sections 54 ₀ and 54 ₁ , respectively, and selects the main signal clock 113 as shown below. The selected clock switching signal 112 is generated.

FIG. 6 shows an outline of the selection process of the clock reception selection unit 55. In other words, the 0-system operation state 120 of the clock distributor indicated by the own system operation state signal 61 ₀ from the 0-system clock distributor 54 _0, indicated by the own system operation state signal 61 ₁ from 1 system clock distributor 54 ₁ The main clock signal selection system 122 indicates which system is selected as the main clock signal, corresponding to the operation state 121 of the 1-system clock distribution unit. For example, the 0-system clock distributor 54 ₀ in a production system, when 1 system clock distributor ₅₄₁ is non-active, selecting the 0-system selection clock signal 60 ₀ as a main clock signal 113 at the clock reception selecting section 55 Is shown. When both systems are operating systems, the clock reception selection unit 55 does not switch the selected system as the main clock signal 113 (previous value holding).

Hereinafter, the operation of the clock switching system including the clock distribution unit according to the above-described embodiment will be described.

Transmission of system 0 and system 1 clocks of basic unit 50
Part 53₀, 53₁Then, 0 system and 1 system clock respectively
A signal is generated. 0 system clock signal is 0 system cable
52 ₀For the system 0 and system 1 clocks of the extension unit 51 via
Distributor 54₀, 54₁Is input to The 1 system clock signal is
1 system cable 52₁0 and 1 of the additional unit 51 via
System clock distribution unit 54₀, 54₁Is input to

System 0 and system 1 clock distribution units 54 ₀ , 5
In 4 _1, the clock signal of one system clock signal selection unit is selected to distribute the clock signal to clock reception selecting section 55.

In each system clock distribution unit, the system clock signal selected by the clock signal selection unit is also input to the clock abnormality detection circuit. When the abnormality of the selected clock signal is detected, the control unit 56 is notified via the control bus 33 as an alarm. When receiving the alarm, the control unit 56 switches the clock signal via the control bus 33 so that the clock selection circuit of the detected system selects the other system.

In the clock distribution unit of each system, when an internal failure is detected by the self-failure detection circuit, the control bus 3
3 to the control unit 56 as an alarm. Control unit 5
6 receives the alarm and switches the system via the control bus 33 and the individual control signal line so that the detected clock distribution unit becomes the non-operational system.

Further, in the clock distribution units of the respective systems, 0
When the disconnection state of the cable to which the clock signal of each system is supplied is detected by the system and system 1 cable disconnection detection circuit, it is notified as an alarm to the control unit 56 via the control bus 33. When receiving the alarm, the control unit 56 switches the clock signal via the control bus 33 so that the clock selection circuits of both systems select a system in which the cable disconnection state is not detected. Further, the system switching is performed via the control bus 33 and the individual control signal line to the clock distribution unit operating as the active system by selecting the clock signal in which the cable disconnection state is detected so that the clock distribution unit becomes the non-active system. Do.

When the switching of the clock signal is instructed by the clock selection circuit via the control bus, the clock distribution unit of each system determines which of the clock signals of both the systems should be used in accordance with the clock selection signal output from the control bus IF. One of the clock signals is selected. Further, when system switching is instructed via the control bus, an operation / non-operation switching control signal is output from the control bus IF to the operation / non-operation switching circuit. In addition, since system switching is instructed by an individual control switching control signal via an individual control signal line at the same time, the noise is once removed by a noise removing circuit and then input to a suppression circuit.
The suppression circuit, when the disconnection state of the cable of either system is detected by the 0-system or 1-system cable disconnection detection circuit,
The switching control signal for individual control input from the noise elimination circuit is masked.

According to the suppression switching control signal output from such a suppression circuit and the operation / non-operation switching control signal, the operation / non-operation switching circuit exchanges its own operation with the clock distribution unit of the other system. Exclusive control is performed by transmitting and receiving the self-system operation status signal indicating the status, and system switching is performed as shown in FIG. That is, when a cable disconnection occurs, an alarm is detected by the clock distribution units of both systems. In response to this, even if the control unit issues a system switching instruction via the control bus, the system shown in FIG.
No system switching is executed as shown in FIG. Even if the control bus becomes incapable of system switching control for some reason, since the individual switching control signal is masked by the suppression circuit when the cable disconnection is detected, noise in both systems due to a transient change such as disconnection of the cable. It is possible to avoid a situation in which system switching occurs due to the difference in the way in which the system is removed.

One of the selected clock signals distributed by the system switching corresponding to various alarms in each clock distribution unit is selected by the clock reception selection unit 55 as a main clock signal in accordance with FIG.

As described above, the clock distribution circuit according to the present embodiment uses the clock distribution unit to detect an abnormal clock signal, a failure in the clock distribution unit itself, and a disconnection state of the cable to which the clock signal is supplied, and provide an alarm to the control unit. Notice.
In response to this, when a failure of the control bus 33 or the clock distribution unit itself or a disconnection state of the cable is detected, the control unit 56 instructs system switching via the control bus and the individual control signal line. When the disconnection state of the cable of each system is detected, the individual switching control signal is masked for the system switching instructed by the individual control signal line from the control unit 56 via the control bus. That is,
Even if system switching is instructed via the control bus when cable disconnection is detected, execution of system switching can be prevented from being performed by the same exclusive control as in the past. However, when there is a transitional change such as disconnection of the cable, only the individual switching control signal is masked so that, for example, a situation in which the 0-system cable is disconnected while the 0-system clock signal is in the operating system. However, it is possible to avoid such a situation that the disconnection of the cable is detected in both systems, but the system switching is performed when the switching instruction to the protection system is first received by the system 0 clock distribution unit.

[0073]

As described above, according to the first aspect of the present invention, when the disconnection state of the transmission line to which the clock signal with the transient change is supplied is detected by the redundant clock distribution circuit. Thus, it is possible to avoid a situation in which only one of the systems is switched to the non-working system first due to a slight timing difference.

According to the second aspect of the present invention, in addition to the effect of the first aspect of the present invention, the switching control to another system is performed even when an abnormality of the clock signal to be further distributed is detected. Thus, the clock signal can be distributed in a stable state.

According to the third aspect of the present invention, in addition to the effect of the second aspect of the present invention, when the failure of the clock distribution circuit itself is detected, the switching control to the protection system is performed. Thus, distribution of a clock signal that degrades reliability can be avoided.

According to the fourth aspect of the present invention,
Since the invention according to claim 1 is applied to a clock switching system, it is assumed that system switching is instructed via a control bus when a disconnection state of a transmission line to which a redundantly configured clock signal is supplied is detected. Also, it is possible to prevent the system switching from being performed by the same exclusive control as in the related art. That is, when the system switching by the control bus is not possible and, for example, accompanied by a transient change such as disconnection of a cable as a transmission line, only the individual switching control signal is masked so that, for example, the 0 system clock signal In a situation where the cable break of the system 0 occurs in the state of the active system, the cable break is detected in both systems, but the switching instruction to the non-working system is first received by the system 0 clock distribution unit, and the system A situation in which switching is performed can be avoided.

According to the fifth aspect of the present invention, in addition to the effect of the fourth aspect of the present invention, even when an abnormality of the clock signal to be distributed is detected, switching control to another system is performed. Thus, the clock signal can be distributed in a stable state.

According to the sixth aspect of the present invention,
In addition to the effect of the invention described in claim 5, even when a failure of the clock distribution circuit itself is detected, the switching control to the non-working system is performed to avoid the distribution of the clock signal that degrades the reliability. can do.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an outline of a configuration of a clock switching system to which a clock distribution circuit according to an embodiment of the present invention is applied.

FIG. 2 is a block diagram illustrating a main configuration of a clock distribution unit according to the embodiment.

FIG. 3 is a configuration diagram illustrating a main configuration of a control unit according to the present embodiment.

FIG. 4 is a flowchart illustrating an outline of processing content of switching control of a control unit in the embodiment.

FIG. 5 is a configuration diagram illustrating a main configuration of a clock reception selection unit according to the embodiment;

FIG. 6 is an explanatory diagram illustrating an outline of a selection process of a clock reception selection unit according to the embodiment.

FIG. 7 is a block diagram illustrating an outline of a configuration of a conventional clock distribution circuit.

FIG. 8 is an explanatory diagram illustrating an outline of system switching control in an operation / non-operation switching circuit.

[Explanation of symbols]

50 base portion 51 expansion units 52 ₀ 0 system cable 52 ₁ 1 system cable 53 ₀ 0 system clock transmission section 53 ₁ 1 system clock transmission section 54 ₀ 0 system clock distributor 54 ₁ 1 system clock distributor 55 clock reception selecting section 56 Control unit 57 ₀ 0 system clock signal 57 ₁ 1 system clock signal 58 ₀ 0 system cable disconnection detection signal line 58 ₁ 1 system cable disconnection detection signal line 59 ₀ 0 individual control switching control signal 59 ₁ 1 individual control switching Control signal 60 ₀ , 60 ₁ Own system operation state signal 61 ₀₀ 0 system selection clock signal 61 ₁ 1 system selection clock signal 70 ₁ , 70 ₂ First and second clock signal input terminals 71 Clock selection circuit 72 Clock selection signal

Continuation of front page (56) References JP-A-2000-324090 (JP, A) JP-A-11-112484 (JP, A) JP-A-8-65360 (JP, A) JP-A 8-65359 (JP, A) A) JP-A-7-64666 (JP, A) JP-A-3-165134 (JP, A) JP-A-3-16335 (JP, A) JP-A-2000-322148 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G06F 1/04 303 G06F 11/20 310 G06F 11/30 320 H04L 1/22 H04L 7/00

Claims (6)

(57) [Claims] 1. A clock selecting means for selecting and distributing any one of a redundantly configured 0-system clock signal and a 1-system clock signal, and providing the 0-system and 1-system clock signals for each of the redundantly configured systems. A disconnection state detecting means for detecting a disconnection state of a transmission line for supplying, and a disconnection state occurrence alarm via a predetermined control bus when the disconnection state detection means detects a disconnection state of any of the transmission lines of the system. A disconnection state occurrence alarm notifying means, and a corresponding to the disconnection state occurrence alarm notified by the disconnection state occurrence alarm notification means via an individual control signal line provided separately from the predetermined control bus. Noise removing means for receiving a first system switching instruction signal for instructing system switching, removing a noise component added to the first system switching instruction signal, and outputting the signal as an individual switching control signal; The clock signal selected by the clock selection means is switched to the other system based on the clock switching instruction signal received in response to the disconnection state alarm notified by the disconnection state alarm notification means via Clock selection control means; and system switching similar to the first system switching instruction signal received in response to the disconnection state occurrence alarm notified by the disconnection state occurrence alarm notification means via the predetermined control bus. Operating state switching means for switching the operating state of the own system based on a second system switching instruction signal for instructing the operation, the individual switching control signal, and the operating state of the other system to be exclusively controlled, and the disconnection state detecting means Inhibiting means for inhibiting system switching control of the operation state switching means by the individual switching control signal when a disconnection state of any transmission path of the system is detected by the The clock distribution circuit, characterized by Bei. 2. A clock abnormality detecting means for detecting an abnormality of a clock signal selected by said clock selecting means, and said predetermined control bus when an abnormality of said selected clock signal is detected by said clock abnormality detecting means. Clock abnormality occurrence alarm notifying means for notifying a clock abnormality occurrence alarm via the control unit, wherein the clock selection control means is configured to control the clock abnormality occurrence notified by the clock abnormality occurrence alarm notification means via the predetermined control bus. 2. The clock distribution circuit according to claim 1, wherein a clock signal selected by said clock selection means is switched to another system based on a clock switching instruction signal received in response to an alarm. 3. A failure detecting means for detecting occurrence of an internal failure, and a failure occurrence alarm notifying means for notifying a failure occurrence alarm via the predetermined control bus when the failure occurrence is detected by the failure detection means. The noise removal unit receives a third system switching instruction signal for instructing system switching in response to the failure occurrence alarm notified by the failure occurrence alarm notification unit via the individual control signal line, and In addition to removing the noise component added to the system switching instruction signal of No. 3 and outputting the same as an individual switching control signal, the operation state switching unit is configured to notify the operation status switching unit of the failure occurrence alarm notification unit via the predetermined control bus. When a fourth system switching instruction signal for instructing system switching is received in the same manner as the third system switching instruction signal in response to the failure occurrence alarm, the system is switched to the non-working system. The clock distribution circuit according to claim 2, wherein 4. System 0 and system 1 clock transmitting means for transmitting redundant system 0 and system 1 clock signals, and system 0 and system 1 transmission for supplying the system 0 and system 1 clock signals, respectively. And a clock selecting means for selecting and distributing one of the clock signals transmitted by the 0-system and 1-system clock transmitting means, and disconnecting the transmission path for supplying the clock signal for each of the systems. Disconnection state detection means for detecting a state, and disconnection state occurrence alarm notification for notifying as a disconnection state occurrence alarm via a predetermined control bus when a disconnection state of any one of the transmission lines of the system is detected by the disconnection state detection means Means and a system disconnection corresponding to the disconnection state alarm notified by the disconnection state alarm notification means via an individual control signal line provided separately from the predetermined control bus. Noise removal means for receiving a first system switching instruction signal instructing the first system switching instruction signal, removing a noise component added to the first system switching instruction signal, and outputting the signal as an individual switching control signal, and the predetermined control bus. Clock selection control for switching a clock signal selected by the clock selecting means to the other system based on a clock switching instruction signal received in response to the disconnection state occurrence alarm notified by the disconnection state alarm notification means Means for instructing system switching in the same manner as the first system switching instruction signal received in response to the disconnection state occurrence alarm notified by the disconnection state occurrence alarm notification means via the predetermined control bus. Operating state switching means for switching the operating state of the own system based on the second system switching instruction signal, the individual switching control signal, and the operating state of the other system that is exclusively controlled; Suppression means for suppressing system switching control of the operation state switching means by the individual switching control signal when a disconnection state of any of the transmission lines of the system is detected by the disconnection state detection means, and And the second system switching instruction signal and the second system switching instruction signal via the predetermined control bus based on the 0-system and 1-system clock distribution circuits, System switching control means for transmitting a clock switching instruction signal and the first system switching instruction signal via the individual control signal line; and a clock selected by clock selecting means of the 0-system and 1-system clock distribution circuits And clock reception selecting means for generating a main clock signal which is selectively selected according to an operation state of the clock distribution circuit of each system among the signals. Clock switching system to be. 5. The clock distribution circuits of the 0-system and 1-system each include a clock abnormality detection unit that detects abnormality of a clock signal selected by the clock selection unit, and a clock selected by the clock abnormality detection unit. Clock abnormality occurrence alarm notification means for notifying a clock abnormality occurrence alarm via the predetermined control bus when a signal abnormality is detected, wherein the clock selection control means The system switching control is performed by switching a clock signal selected by the clock selection unit to the other system based on a clock switching instruction signal received in response to the clock abnormality occurrence notification notified by the abnormality occurrence notification unit. Means for generating the abnormal clock signal notified from the 0-system and 1-system clock distribution circuits. The clock switching system according to claim 4, wherein the clock switching instruction signal is transmitted via the predetermined control bus based on a raw alarm. 6. The 0-system and 1-system clock distribution circuits each include a failure detecting means for detecting occurrence of an internal failure, and a predetermined control bus when the failure detection means detects the occurrence of a failure. A failure occurrence alarm notifying unit for notifying a failure occurrence alarm, wherein the noise removing unit instructs system switching in response to the failure occurrence alarm notified by the failure occurrence alarm notifying unit via the individual control signal line. Receiving the third system switching instruction signal to remove the noise component added to the third system switching instruction signal and outputting the same as an individual switching control signal, and the operation state switching means is configured to receive the predetermined control bus signal. A fourth system disconnection commanding system switching in the same manner as the third system switching instruction signal received in response to the failure occurrence alarm notified by the failure occurrence notification unit via 6. The clock switching system according to claim 5, wherein when the switching instruction signal is received, the clock switching system switches to a protection system.