JPH0748735B2 - Data communication method - Google Patents

Description

The present invention relates to a data communication system for efficiently transmitting data having different update cycles by utilizing a token passing bus.

[Conventional technology]

Local area network (hereinafter referred to as LAN) has been rapidly spreading in recent years, and one of the notable trends in this area is MA proposed by General Motors (GM) of the United States.
There is a growing interest in industrial LANs called P (Manufacturing Automation Protocol). FA
(Factory Automation Factory Automati
on), OA (Office Automation)
A lot of devices such as robots and computers have been installed in factories and offices for the purpose of ion), but for the purpose of connecting these devices easily and inexpensively, the MAP
Is being standardized. It aims to be an industry standard rather than a one-company LAN, and many leading companies are participating. ISO (International Organization for Standardization) OSI (Open Systems Interconnec)
standardization is underway by filling each layer of the hierarchical model, and the lower two layers (physical layer, data link layer) except for the theoretical link control sublayer are IEEE (The Institute of Electrical and Electronic Engineers of the United States The Institute). of Electrical and
Electronics Engineers Inc.) 802.4 Committee token passing bus is used. At present, the IEEE802.4 standard uses a coaxial cable as a physical layer transmission medium, but the application of an optical fiber cable is also under consideration, and the medium is an optical fiber cable or a data link layer communication method. Exactly the same.

FIG. 2 is a block diagram showing a network in which the token passing bus is composed of an optical fiber cable. In the figure, 1 ₁ to 1 _n are stations that make up the network, and 2 ₁ to 2 _n
Is an optical fiber cable, and 3 is an optical star cutter.

Next, the operation will be described. Although there is a method (CSMA / CD) in which each station arbitrarily sends data in the bus type network, there is a drawback that the transmission efficiency decreases rapidly when the amount of transmission data increases and the load increases. The token passing bus, on the other hand, avoids this drawback by a deterministic access scheme. That is, a transmission right called a token is sequentially transmitted among the stations that are subscribing to the token passing bus, and it is possible to prevent a plurality of stations from transmitting at the same time. Tokens are passed in order from the station with the largest address to the station with the smallest address, and each station remembers the station (succeeding station) to which it should give the token, which makes the token a logical ring (logical ring). Is configured. However, if this logical ring is fixed, it will not be possible to join when a new station wants to join, and if any of the joining stations fails, the logical ring will break and communication will stop. Therefore, the token passing bus has the following ring maintenance function.

(1) When the token temporarily disappears due to noise or the like, the previous token holding station reissues the token.

(2) When the succeeding station fails, give the token to the succeeding station of the failing station and remove the failing station from the logical ring.

(3) The solicitation of the master station is conducted at almost constant intervals, and the stations wishing to join the logical ring are permitted to join.

On the other hand, there is an application field for transmitting measurement information and high-speed control of equipment by using this token passing bus, but when actually using the token passing bus for the above application, for example, The control command of the breaker and the breaker is 1-2 m
It needs to be transmitted within s, but it is necessary to transmit data with different update periods on the same bus, such as transmitting measurement information such as current and voltage at time intervals of 20 ms to 50 ms.

In the token passing bus method, the content of the data to be transmitted is determined by the user, but generally, data having different update cycles are mixed. First, the third of the general transmission methods that does not consider the update cycle of data to be transmitted.
This will be described with reference to FIG. 4 and FIG.

Figure 3 shows the conventional IEEE (IEEE)
It generally represents the status of data transmission on the bus by the 802.4 committee's token passing bus method. ▲ D ^j _i ▼ is a data frame sent by the station 1 _i in the j-th cycle, and ▲ T ⁱ _j ▼ is a token frame sent by the station 1 _i to the station j. In addition, the cycle here is
The token passes over each station once, and indicates the period during which each station sends a data frame. Further, the address value of station 1 _i is i. Figure 4 shows the structure of the data frame, which is as specified by the IEEE 802.4 committee.

Below, preamplifier (PR) other than the data part in this data frame, starting delimiter (SD), frame control (FC), decision address (D)
A), source address (SA), frame check sequence (FCS), and ending delimiter (ED) are called transmission control information for convenience. Here, as an application example, consider the case where the amount of data to be transmitted generated at each station and the update cycle of the data are as follows.

○ Station 1 _l to Station 1 _{(k + 1)} : Data volume …… ni octet (i =
(K + 1) to l) Update cycle ... Every cycle ○ Station 1 _k to Station 11 ₁ : Data amount …… mj octets (j = 1 to 1)
k) Update cycle ... M cycle Here, the relationship between k and M is as follows.

k <M such cases, method is conceivable to evenly transmit the data each time to obtain a 1 ₁ to station 1 all stations every cycle transmission right to _l station. That is, the following transmission methods are possible.

○ Station 1 _l to station 1 _{(k + 1)} have ni octets (i =
After the data of (k + 1) to l) is generated, the data is temporarily stored, and this data is transmitted when the transmission right is obtained in each cycle.

○ Stations 1 _k to ₁₁ are mj octets to be transmitted (j = 1 to k)
After the data is generated, the data is temporarily stored, and each time the transmission right is obtained, mj / M octets are divided into M times and transmitted.

[Problems to be Solved by the Invention]

Since the conventional data communication system by the token passing bus system is configured as described above, the frame of the token passing bus has the same transmission control information regardless of the data amount as in the fourth case. Therefore, there is a problem that lowering the transmission efficiency becomes much smaller station data amount to be transmitted, in which case, for transmission efficiency, update cycle is a data station 1 _k ~ station 1 ₁ is M cycles It is possible to send all the data at once in every M cycles instead of sending the data every cycle, but in this case, the token rotation time becomes long, so the token hold in the next cycle. -There was a possibility that some stations could not send data due to the time being out of time.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a data communication system capable of efficiently sequentially transmitting data having different update cycles.

[Means for Solving the Problems]

In the data communication system according to the present invention, the master station of the station on the network transmits a counter set command to a plurality of slave stations on the network at a constant number of transmissions, and each slave station follows the received counter set command. Then, set the counter of the own station to a value common to each station, increment the counter every token pass, and send the data frame only when the value of this counter becomes equal to the address value of the own station. It was done.

[Action]

In the data communication system according to the present invention, a station that also sends data with a long update cycle is controlled not to send data each time it obtains a transmission right, but to send data only in the cycle that matches the update cycle. , The total number of data frames to be transmitted is reduced, and data having a long update period is collected and transmitted, thereby improving the transmission efficiency.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
The figure is an explanatory view generally showing the transmission status of data on the bus in the data communication system according to the present invention. In the figure, ▲ D ^j _i ▼ is a data frame sent by the station 1 _i in the j-th cycle, and ▲ T ⁱ _j ▼ is a token frame transmitted from the station 1 _i to the station 1 _j , and has the same notation as in the case of the conventional token passing bus system shown in FIG.

Next, the operation will be described. The amount of data to be transmitted at each station and the update period of the data are the same as those described in the prior art, and each station operates as follows.

Station 1 _l is the master station, has a counter set command flag in its data frame, and sends a counter set command to other stations once every k * M cycles, and nl every cycle.
It sends out data that is updated every cycle of an octet. Station 1 _(l-1) to station 1 _{(k + 1)} have ni (i
= (K + 1) to (l-1)) Data to be updated is sent every cycle. Stations 1 _k ~ station 1 _1, mi is updated every M cycles (j = k~1) data octet is generated. Based on the counter set command flag of the master station 1 _l , the stations 1 _k to ₁₁ can set their own counters (M-
Set to 1). Stations 1 _k ~ station 1 ₁ After receiving own station token, if the counter value and the address of its own station of the mobile station are equal sends data of mj (j = k~1) octet, the own station counter value Is decremented by “1” and the token is passed. If the counter value of the local station and the address value of the local station are different, data is not sent, the counter value of the local station is decremented by "1", and the token is passed. When the counter value of the own station is "0", the value (M-1) is reset instead of the subtraction.

FIG. 1 will be described for each cycle.

<First cycle> The master station 1 _l issues a counter set command to the other stations by using ▲ D ¹ _l ▼. Stations 1 _k ~ station 1 ₁ is excisional the counter receives the _{^{▲ D 1 l ▼ (M-}} 1). Station 1 _(l-1) to station 1 _{(k + 1)} sequentially send data ni (i = (l-1) to (k + 1)) octets and pass the token. Station 1 _k then receives the token and compares it with its own counter value. Since the counter value of the own station is (M-1) and does not match the address value of the own station, data is not transmitted, the token is passed, and the counter is decremented. The following station _{1 (k-1)} ~ station 1 _1, according to the station 1 _k, work,
No station sends data.

<Second cycle> The master station 1 _l does not issue the counter set command at ▲ D ² _l ▼.
Station 1 _(l-1) to station 1 _{(k + 1)} send data according to the first cycle. Operation of the station 1 _k ~ station 1 ₁ is described in the next section <third cycle, second (M-1) cycles>.

<Third to (M-1) th cycle> Stations 1 _l to 1 _{(k + 1)} are the same as the second cycle.

Stations 1 _k ~ station 1 _1, while comparing the match address value and the counter of the own station, for sending data of mj (j = 1~k) octet only when the match, the station following each cycle Only send data.

Cycle (M-k): Station 1 _k Cycle (M-k + 1): Station 1 _(k-1) : i-th cycle: Station 1 _(Mi) : Cycle (M-2): Station 1 ₂ ( M-1) cycle: the station 1 ₁ <M th cycle> station 1 _l ~ station 1 _{(k + 1)} is the same as the second cycle.

Stations 1 _k ~ station 1 _1, the counter value does not send data for "0". After the token pass, the counter is not decremented (M-
1) Set to the value. After the (M + 1) th cycle, the above 1st to Mth cycles are repeated.

However, since the counter set command of the master station 1 _l is sent once every k * M cycles, which is a multiple of M cycles, the counter of each station is forced (M
-1) is set.

In the above embodiment, the subtraction timing of the counter is defined as after the token pass of the own station, but this timing is
It may be a simultaneous broadcast frame sent by the master station,
The same effect as in the above embodiment can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the data communication method is
Each station increments the counter value each time it makes a token pass and sends data only when the counter value is equal to the address value of its own station, so many stations send data in one cycle. Is prevented. In particular, when the set value (M-1) of the counter is equal to or larger than the number of stations k, only one station out of k stations transmits data in one cycle. Therefore, even if a station that generates a large amount of data with a long update cycle sends the data all at once,
In other stations, the situation in which data is lost due to the generation of new data before the data is transmitted and the data is lost does not occur. Therefore, there is no need to divide and send the data, and it is possible to prevent a decrease in transmission efficiency. In addition, since the station that transmits data in a certain cycle is determined in advance, there is an effect that data processing accompanying data transmission and reception is simplified.

[Brief description of drawings]

FIG. 1 is an explanatory view of a data transmission state showing a data communication system according to an embodiment of the present invention, FIG. 2 is a configuration diagram of an example of a bus type network to which the present invention is applied, and FIG. 3 is a conventional IE.
FIG. 4 is an explanatory view of a data transmission state showing a data communication system using a token passing bus of the EE 802.4 committee, and FIG. 4 is a configuration diagram of the conventional data frame shown in FIG. 1 ₁ , 1 ₂ ..., 1 _n is a station, 2 ₁ to 2 _n are optical fiber cables, 3 is an optical star cutler. In the drawings, the same reference numerals indicate the same or corresponding parts.

Front page continuation (72) Inventor Tadao Matsumoto 1-3-3 Uchisaiwaicho, Chiyoda-ku, Tokyo Within Tokyo Electric Power Co., Inc. (72) Innovator Shintomi Ohashi 1-3-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Tokyo Electric Power Company Incorporated (72) Inventor Katsuki Sano 1-1-1, Kokubuncho, Hitachi City, Ibaraki Hitachi Co., Ltd. Kokubun Factory, Hitachi Ltd. (72) Inventor Tatsuya Kano, No. 1, Toshiba Town, Fuchu City, Tokyo Toshiba Fuchu Factory, Ltd. (72) Inventor Yasuhiko Terao 1-2-2 Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Electric Corporation Control Works

Claims (1)

[Claims] 1. In a data communication system in which each station on the network sequentially delivers a token and the station which has obtained the token sends data to the network, the main station on the network counters every fixed number of transmissions. A set command is transmitted to a plurality of slave stations on the network, and the plurality of slave stations are
According to the received counter set command, the counter of the own station is set to a value common to a plurality of slave stations, and the counter value is incremented each time the token pass is made, and when the counter value is equal to the address value of the own station. A data communication method characterized by transmitting only data.