JPH0279637A - Signal synchronizing system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a signal synchronization method, and in particular, uses a token passing bus to transmit instantaneous values of, for example, voltage, current, etc. at multiple points apart from each other. The present invention relates to a signal synchronization method suitable for use in generating sampling signals etc. for simultaneously determining .

[Prior art] Local area networks (LANs) have been rapidly spreading in recent years, and one of the technologies that deserves particular attention is M
A P (Manufacturing Auton
An industrial LA called +ationProtocol)
N is known.

The purpose of this MAP is to easily and inexpensively interconnect equipment such as robots and computers installed in factories, offices, etc. for FA, OA, etc., and its standardization is progressing. .

This standardization is based on 08I (O
pen Systems Interconnecti
on) Progress is being made by filling in each layer of the hierarchical model,
For the lower two layers (physical layer, data link calendar) excluding the theoretical link control sublayer, a token passing bus of the IEEE (American Council of Electrical and Electronics Engineers) 802.4 committee is used.

The token passing bus and signal transmission will be explained below with reference to the drawings.

Figure 3 shows the axis side of the transmission signal of the token passing bus that performs signal synchronization, Figure 4 shows an example of a bus type network using coaxial cables, and Figure 6 shows the number of stations joining the network. It is a figure which shows the example of a transmission signal when there are few. In FIG. 4, 1□ to 1fi are subscriber stations, 2 is a coaxial cable, and 3□ to 3a are branching devices.

In FIG. 4, subscriber stations 11 to 11 constituting the network
1° is connected to the coaxial cable 2 via branch devices 3□ to 3fi called taps.

In this type of bus network, there is also a method (CSMA/CD) in which each connected subscriber station transmits data arbitrarily, but with this method, as the amount of transmitted data increases and the load increases, the transmission efficiency decreases. It has the disadvantage of rapidly decreasing. On the other hand, the token passing bus to which the present invention is applied can avoid this drawback by using a deterministic access method. In other words, in this token passing bus, information indicating a transmission right called a token is passed in order between each subscribing station that has joined the token passing bus, and multiple subscribing stations simultaneously transmit at the same time. It is prevented. The token can be e.g.
The token is passed in order from the station with the largest address to the station with the smallest address, and each subscribing station remembers the subsequent subscribing station to which it should pass the token. ring) is configured. but,
If this logical ring is fixed, new stations will not be able to join the bus even if they wish to do so.
Furthermore, if any of the subscriber stations fails, the logical ring will be broken and communication will stop. To avoid this, the token passing bus is equipped with the following rig maintenance function.

(1) If a token is temporarily lost due to noise or the like, the subscriber station that held the previous token reissues the token.

(2) If the subsequent subscriber station to which the token should be passed fails, the token-issuing subscriber station passes the token to the successor station of the failed subscriber station, and removes the failed subscriber station from the logical ring.

(3) New stations are solicited at regular intervals, and stations that wish to join the logical ring are allowed to join.

On the other hand, there are application fields in which high-speed control of equipment is performed using a LAN including this token passing bus, and among these are systems that require each subscriber station to repeatedly generate a specific signal at the same time. For example, sampling signals are generated to simultaneously obtain instantaneous values of voltage, current, displacement, acceleration, etc. at multiple points. Therefore, by using a token passing bus using a LAN, such specific signals,
For example, if it were possible to perform signal synchronization of sampling signals, the token passing bus would have the advantages of instantaneousness, self-healing, and scalability.

In addition, the uses of the token passing bus can be further expanded.

As a method of performing signal synchronization as described above using a token passing bus, a specific subscriber station that makes up the network is designated as the master station, and data frames periodically emitted by this master station are used to synchronize signals other than the master station. There is a method in which other participating stations (slave stations) synchronize with the master station and generate specific signals such as sampling signals.

Now, in FIG. 4, it is assumed that the subscriber station 11 is the master station, the other subscriber stations 1□-16 are slave stations, and the subscriber stations 1□-1° including the master station transmit data. In this case, as shown in FIG. 3, the subscribing station 1, which is the main station, first transmits a data frame request and then a token T request. A subscribing station that is a slave station that is logically positioned after the master station, e.g.
Joined station 1□ is.

Detecting the token T1 from this main station, confirming that the transmission right has been transferred to the own station, and transmitting the data frame D2,
In order to transfer the transmission right to the subsequent subscriber station, the token T
, is sent. When such operations are performed by all subscriber stations, the transmission right is transferred again to subscriber station 1□, which becomes the main station, and the above-described operations are repeated.

By the way, it is assumed that the subscriber station 1□, which becomes the main station, generates a synchronization signal (hereinafter referred to as the main synchronization signal) S□, which is generated for a specific signal such as a sampling signal, with a period T, and this becomes the main station. If the joining station 1□ can transmit the data frame load in synchronization with this main synchronization signal S, the joining stations 12 to 1. can know the generation time of the main synchronization signal S4 based on the reception time of the data frame processing, and generates own station synchronization signals S,, S, etc. in synchronization with this main synchronization signal S□. be able to. That is, in the token passing bus, data frame processing can be received by all slave stations almost simultaneously by appropriately setting the destination address.

In order to realize the signal synchronization described above, subscriber station 1, which is the main station,
1, there is a problem in how to transmit a data frame synchronized with the main synchronization signal S□.

Originally, the tokens on the token passing bus circulate according to an algorithm to maintain the logical ring, and the dark period of the cycle is of course different from the period T of the main synchronization signal S1, and is also caused by solicitation of new stations, token passing retries, etc. Since it is performed stochastically, it always fluctuates. Therefore, in order to perform the above-mentioned signal synchronization using the token passing bus, it is essential to have a means to enable the subscribing station 11, which is the main station, to transmit data frame processing in synchronization with the main synchronization signal S□. be. As one method, the main station and the subscriber station 1□
A conceivable method is to make the transmission of the data frame D1, which should be immediately transmitted, wait until the time when the main synchronization signal S is generated after receiving the token and obtaining the right to transmit. However, with this method, the no-signal state continues for a long time, and the previous subscriber station that sent the token to the subscriber station 11, which is the main station, assumes that the token passing has failed and retransmits the token. There is a problem in that the joining station 1□, which is the main station, is considered to be faulty and removed from the logical ring.

As a method to solve such problems, the master station transmits an empty data frame D before transmitting the data frame D, and the length of this empty data frame D is determined based on the master station's token reception time. There is a method of adjusting the transmission time of the data frame D□ by changing the transmission time according to the data frame D□. However, this method causes the following problem when the number of stations joining the network is small.

FIG. 6 is a diagram showing transmission signals when the number of stations joining the network is two including the main station, and in this diagram,
When the subscribing station 11, which is the master station, transmits a token Ti after transmitting a data frame synchronized with the main synchronization signal S, the slave station detects this token T, transmits a data frame D, and then sends a token T2. Send. Assuming that the number of stations joining the network is 2, the joining station 1 becomes the main station.
□ obtains the transmission right with this token Tyu, and must immediately start transmitting the empty data frame D1. However, in this case, the token T
Since the time tlNT from when the token T2 is sent until the token T2 destined for the own station arrives again is short, the subscribing station 1□, which becomes the main station, calculates the length of the empty data frame, which must be done during this time. However, there may be cases where the processing to add to the head of the transmission queue is not done in time. In this case, synchronization cannot be maintained using the method described above.

As explained above, the synchronization between the data frame D1 transmitted by the subscriber station 1□ serving as the main station and the main synchronization signal S is as shown in FIGS. 3 and 6. The end time is controlled to be the synchronization position of the main synchronization signal S□.

[Problem to be Solved by the Invention] As mentioned above, in the conventional technology, when the number of stations joining the network is small, the token arrives before the main station completes calculation of the empty data frame length, etc. In this case, there is a problem that signal synchronization cannot be maintained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal synchronization method that solves the problems of the prior art and can reliably maintain signal synchronization even when the number of stations joining a network is small.

[Means for Solving the Problems] According to the present invention, the above object is achieved by causing slave stations to also transmit empty data frames when the number of stations joining the network is small.

[Effect] By transmitting an empty frame in the slave station, the time required for the master station to receive the token and obtain the next transmission right after transmitting the token increases, and the time required for calculating the frame length of the empty data frame and transmitting it increases. It becomes possible to secure sufficient time to perform the preparation process. Therefore, signal synchronization can always be maintained reliably.

[Embodiment] Hereinafter, an embodiment of the signal synchronization method according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram illustrating signal transmission according to an embodiment of the present invention when the number of stations joining the network is two, and FIG. FIG. 3 is a diagram illustrating signal transmission according to an embodiment.

The network to which the present invention is applied includes, as conventional technology,
It has the same configuration as explained with reference to FIG. 4, and in the following explanation, the subscriber station 11 will be regarded as the main station regarding signal synchronization, and the other subscriber stations 12 to 1. is the subordinate station. Then, joining stations 12-1. The address given to the token is arbitrarily assigned regardless of its accommodation position, and the tokens are sequentially moved according to this address.

In FIG. 1, the subscribing station 11, which is the main station, synchronizes with the main synchronization signal S to frame a data frame (hereinafter referred to as "S").

A data frame synchronized with the main synchronization signal in this main station is called a synchronous data frame )D, and then a token T2 is sent. The synchronization data frame D has a fixed frame length, its data pattern is known in advance by all the slave stations that use the synchronization signal, and its destination address is known to all the slave stations that use the synchronization signal. A group address that includes is assigned.

The transmission time of this synchronization data frame D1 is controlled so that the transmission end time is the generation time of the main synchronization signal S1. When the subscribing station 1□, which becomes the slave station, receives the token T, it transfers its own data frame D.
2, it transmits a fixed-length empty data frame DI2, and subsequently transmits its own data frame D2 and token T2.

In the example shown in Figure 1, the number of subscriber stations accommodated in the network is 2, so the subscriber station 11, which becomes the master station, receives the token T2 from the subscriber station 1□, which becomes the slave station. , learns that the transmission right has been transferred to its own station. In order to synchronize the transmission of the synchronization data frame D1 with the next main synchronization signal, the subscriber 1□ serving as the main station needs to transmit empty data frames D and L during that time. Therefore, the subscribing station 1□, which becomes the master station, receives empty data during the time t INT from the end of transmission of the token T□ that it transmits to the reception of the token T2 from the subscribing station 1□, which becomes the slave station. Frame D6
The frame length of , is calculated from the frame length of the previous empty data frame, the error between the synchronization frame transmission end time and the main synchronization signal S4, and the empty data frame IL with the frame length obtained from this result is waiting for transmission. Performs processing to add to the beginning of the matrix. The frame length of the empty data frame D, 2 transmitted from the subscriber station 1□, which becomes the slave station, is the above-mentioned time tlN.
T is set in advance so that it is longer than the processing time for performing the above-described processing at the subscriber station 11 serving as the main station.

When there are a large number of stations joining the network, the time t□, a from the time the master station sends a token until it receives the next token is a sufficiently long time even if no empty data frame is sent from the slave station. Therefore, there is no need to transmit empty data frames from the slave station. FIG. 2 shows the state of signal transmission in this case.

In FIG. 2, the subscribing station 11, which is the main station, transmits a token T1 after transmitting a synchronization data frame D□ synchronized with the main synchronization signal S1. The slave station, which is a subordinate station that has received this token T8, transmits its own data frame D2, and then transmits the token T2 to transfer the transmission right to the subordinate station. Through such operations, when all subscriber stations have finished transmitting data frames, the subscriber station that becomes the lowest transmitting station.

Send token Tn. As a result, the transmission right is transferred to the subscriber station 1□, which becomes the main station again. After transmitting token T4 at subscribing station 1□, which becomes the main station, token T4
In this case, the time trNt until reception of the empty data frame D, is sufficiently large.

During this time, processing such as calculating the frame length of can be increased up to a maximum number determined by

With this configuration, the subscriber station 1□, which is the master station, can always transmit the synchronized data frame in synchronization with the main synchronization signal S1, and all slave stations that can receive this synchronized data frame D1 , it becomes possible to generate a local synchronization signal whose synchronization position is the end point of this synchronization data frame processing. Furthermore, since the joining station that becomes the slave station is equipped with its own station clock, it can predict the time at which it should detect the main synchronization signal S1 from the master station, and if the detected main synchronization signal S1 is If the time is significantly different from the predicted time, it is assumed that an abnormality has occurred in the network and the detected main synchronization signal S1 is ignored. This makes it possible to further improve the reliability of the synchronization signal in the subscribing station that becomes the slave station.

In the embodiment of the present invention described above, there is one slave station that transmits the empty data frame, but the slave station that transmits the empty data frame may be any one of the slave stations accommodated in the network. There may be more than one. Furthermore, whether or not a slave station should transmit an empty data frame may be instructed by the master station to each slave station, depending on the number of subscribed stations accommodated in the network, or each slave station may The determination may be made according to the number of participating stations accommodated in the network, or may be further determined using the frame length of the empty data frame from the main station.

Furthermore, the number of slave stations that transmit empty data frames may be made variable depending on the number of subscribed stations accommodated in the network, or the empty data frames transmitted by slave stations may vary depending on the number of subscribed stations accommodated in the network. It is also possible to make the frame length variable. Further, the empty data frame transmitted by the main station may be divided into two or more parts and transmitted as necessary.

In the embodiment of the present invention, an empty data frame transmitted from a slave station or a master station within the network does not need to be received by any subscriber station, and its destination address is not required to be received by any subscriber station accommodated in the network. It is a group address or an individual address that does not specify any information.

In the embodiment of the present invention described above, when a slave station transmits an empty data frame, the slave station transmits its own data frame after transmitting the empty data frame.
After transmitting the local data frame, an empty data frame may be transmitted.

FIG. 5 is a diagram showing the configuration of another network to which the present invention is applied. In FIG. 5, 4 is an optical star coupler;
5□ to 5U are optical fiber cables, and other symbols are the same as in FIG. 4.

The present invention is applicable not only to a network equipped with the coaxial cable shown in FIG. 4, but also to a network using an optical star coupler 4 and optical fiber cables 5□ to 56, as shown in FIG. 5, for example. can do. Each of the optical fiber cables 5□ to 5° includes two optical fiber cores. In this network, e.g.

The transmission signal from the subscriber station 1□ is transmitted through the optical fiber cable 51.
The signal is sent to the optical star coupler 4 through the transmission fiber of
The participating stations 1□-1. sent to. Although the topology of this network is physically a star shape, it can be treated logically as a bus shape in the same way as in the case of FIG. Although it is a C8MA/CD method and not a document on optical token bus, there is a document on network using star coupler in IEICE National University.
o, 1780 (1984), IEICE Communication Division Zendai No.
177 (1984), etc.

[Effects of the Invention] As explained above, according to the present invention, IEEE802
．． When performing signal synchronization by adjusting the frame length of empty data frames in a 4-token passing bus or a network having a communication protocol similar to that bus,
When the number of subscriber stations accommodated in the network is small, stable signal synchronization can be achieved even when the number of subscriber stations is small by transmitting empty data frames at slave stations as well. If a large number of subscriber stations are accommodated, by stopping the transmission of empty data frames in the slave stations, it is possible to increase the number of subscriber stations up to the maximum number of stations depending on the capacity of the network.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating signal transmission according to an embodiment of the present invention when the number of stations joining the network is two, and FIG. 3 is a diagram illustrating an example of a transmission signal of a token paralleling bus that performs signal synchronization; FIG. 4 is a diagram illustrating an example of a bus-type network using a coaxial cable; FIG. 5 is a diagram showing an example of a network using optical fiber cables, and FIG. 6 is a diagram illustrating signal transmission according to the prior art when the number of stations joining the network is two. 1□~1゜・・・Subscribing station, 2...Coaxial cable, 3□～3...Branch device, 4...
・・Optical star coupler, 5□～5. ...Fiber optic cable. Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a signal synchronization method using an IEEE 802.4 token passing bus or a network having a communication protocol similar to this, a subscriber station that serves as a synchronization master station transmits synchronized data frames from the own station. In order to adjust the transmission time, an empty data frame is transmitted prior to the transmission of the synchronous data frame, and by adjusting the length of the empty data frame, the transmission end time of the synchronous data frame is adjusted to the main synchronous signal. The signal synchronization method is characterized in that, when the number of stations joining the network is small, some or all of the stations that become synchronized slave stations transmit empty data frames. 2. The subscribing station that becomes the slave station of the synchronization synchronizes its own station synchronization signal with the main synchronization signal by detecting the end time of reception of the synchronization data frame. The signal synchronization method described in Section 1. 3. When the number of stations joining the network is small, the joining station that becomes the master station of the synchronization instructs some or all of the joining stations that become the slave stations to transmit an empty data frame. A signal synchronization method according to claim 1 or 2, characterized in that: 4. The signal synchronization system according to claim 1 or 2, wherein the subscribing stations that become slave stations decide whether to transmit an empty data frame based on the judgment of each subscribing station. 5. If the reception end time of the synchronized data frame is earlier or later than the normal scheduled reception end time by exceeding a certain tolerance range, the joining station that becomes the slave station shall receive a synchronization signal generated by this reception end time. The signal synchronization method according to claim 2, 3, or 4, characterized in that the signal synchronization method ignores. 6. The destination address of the empty data frame is a group address or an individual address that does not indicate any synchronized slave station in the network. The signal synchronization method described in any one of the items. 7. Any one of claims 1 to 6, wherein the destination address of the synchronization data frame is a group address that includes all subscribing stations that become synchronization slave stations in the network. Signal synchronization method described in section. 8. The frame length of the synchronization data frame is fixed and known in advance by all subscribing stations that become synchronization slave stations. The signal synchronization method described in any one of the items.