JPH0585096B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is aimed at adjusting the data transmission timing when transmitting data from a plurality of stations via a common transmission path in a building, factory, plant, etc. By managing time, collisions between data sent from each station are avoided.

[Conventional technology]

Proposed by IEEE (Institute of Electrical and Electronics Engineers) 802.3 as a method for sending and receiving data from multiple stations via a common transmission path when constructing a LAN (Local Area Network).
CSMA/CD (Carrier Sense Multiple Access/
A serial data transmission method using collision detection (carrier detection multiple access with collision detection) is conventionally known.

As shown in FIG. 4, this system is a system in which N stations 1 to N are connected to a common transmission line 10 with terminating resistors R1 and R2 connected at both ends. When each station sends data to other stations, it does so as follows.

) A station that intends to transmit data checks whether there is data (carrier) on the transmission line 10.

) If there is no data on the transmission line 10, it immediately sends its own data.

) If there is data on the transmission line 10, wait for a period of time, check again whether there is data on the transmission line 10, and transfer the data to the transmission line 1.
When there is no more data on 0, it sends its own data.

) If a collision with data from another station is detected after the data is sent and before the final bit is sent, the data is retransmitted according to steps) to) above.

[Problem that the invention seeks to solve]

The CSMA/CD method described above does not require a master station that centrally controls the data transmission timing of each station, so the overall system configuration can be simplified, but on the other hand, it has the following drawbacks.

(1) Two or more stations simultaneously connect the transmission line 10
If you check the presence or absence of the above data and determine that it is absent, and then send the data at the same time, a data collision will occur and the data will be destroyed. In this case, the data must be retransmitted as described above).

(2) As the number of stations connected to the transmission line 10 increases, the probability of collision increases extremely.

(3) If each station is a control device in a factory or plant (for example, a boiler burner control device), even if you try to transmit data between each control device, there will be a transmission delay due to collisions, and events such as movement of controlled equipment, etc. ), causing problems with controllability, safety, etc., which impairs real-time performance.

Due to these drawbacks, the CSMA/CD method is
Although it was used for OA (Office Automation), it was not suitable for FA (Factory Automation).

The present invention solves the drawbacks of the conventional technology, and when data is transmitted from a plurality of stations via a common transmission path in a building, factory, plant, etc., the data transmitted from each station is The present invention aims to provide a data sending method in data transmission that can avoid collisions with a simple configuration.

[Means for solving problems]

In this invention, when each station transmits data, it transmits its own identification information, other stations input the identification information, and the data transmission order assigned in advance is set so that the data of each station does not collide with each other. Calculate the timing to send data from your own station according to
When that timing is reached, data and identification information are sent from the own station, and each station updates the timing calculation each time it receives identification information.

[Effect]

According to this invention, a data transmission order is assigned, and each station determines the timing to transmit data in this order based on identification information and transmits data, so data transmission is managed in a time-division manner and data collisions are avoided. Prevented.

Furthermore, since each station determines the timing at which it transmits data in a time-division manner by itself based on identification information, there is no need for centralized control by a master station, simplifying the entire system.

〔Example〕

An embodiment of this invention is shown in FIG. this is,
This is a CSMA/CD system in which the data transmission timing time management function of the present invention is added to an existing microcomputer. A common transmission path 10 (coaxial cable or single line) has N stations 1 to
N is connected. At both ends of this transmission line 10, there are terminating resistors R1 and R2 for erasing data (carrier).
is connected.

Each station 1-N has a unique number
No. 1 to No. N are assigned. Each station 1
~N is this number No.1~No.N when sending data
is sent as identification information. Each station 1 to N also inputs this identification information sent from the other stations.

Each station 1 to N is a number (No.1 to No.N)
The data transmission order is assigned so that data is transmitted from a small station.

Each of the stations 1 to N includes a transmission unit 11, a control calculation unit 12, and an external input/output unit 13, as shown in FIG. The transmission device section 11 sends and receives data to and from other stations 1 to N through the transmission path 10. This internal microcomputer is added with a time management function for data transmission timing according to the present invention. Control calculation unit 12
performs data exchange with the transmission device section 11 and external input/output section 13. In addition, the external state (state of the controlled object) is managed by control calculations. The external input/output unit 13 inputs state (temperature, pressure, etc.) detection signals of an external plant to be controlled and outputs operation command signals for the external plant.

The time management function of the data transmission timing by the microcomputer of the transmission device section 11 will be explained.

The total number of stations is N, the required value of real-time control response of all devices (required I/O cycle for the entire system) is Tc, and the data transmission time interval of each station is set to τ=Tc/N (for example, If N=50 and Tc=100msec, τ=2msec).

Each station 1 to N receives identification information (station numbers No. 1 to No. N) sent together with data from the other stations. The transmission device section 11 of each station 1 to N compares this identification information (receiving station number) with the station number assigned to its own station (its own station number), and determines the data transmission time of its own station as shown below.
Obtained from equation (1).

t=(i-j)τ(when i>j) {Tc-(j-i)}τ(when i<j) (1) However, t: Data transmission time of own station i: Own station number j: Receiving station number Note that the data sending time t is determined as the time from the current time (the time when the station number was received).

When it is detected that the above-determined transmission time has been reached, data is transmitted from that station. At this time, the station also outputs a station number which is identification information, so each station recalculates the data transmission time t from equation (1) based on the above equation. That is, the data transmission time t of each station is updated every time data is transmitted from any station. As a result, if there are a plurality of stations to which data is to be transmitted, data is transmitted one by one in order from the station with the lowest station number.

FIG. 3 shows an example of data transmission using the time management function of the data transmission timing described above. Here, the number of stations is 10, No. 1 to No. 10, and the data to be sent from the station is 3 to No. 2, 1 to No. 4, 2 to No. 7, and 2 to No. 8. Assume that there is one.

Now, if station No. 2 sends out one piece of data and its station number No. 2 at time 2τ, the other stations No. 1, No. 3 to No. 10 will transmit the station number No. 2 and their own data. From the station number, calculate the data transmission time of the own station using equation (1). Note that station No. 2 sets the next transmission time to Tc.

If the transmission time is set for each station in this way, station No. 4 will be the first to reach the transmission time among the stations that are about to transmit data, so when that time 4τ is reached, the station Station number No. 4 is output from No. 4 along with one piece of data. Based on this station number No. 4, each station calculates and updates the sending time in the same manner as above.

In this way, at time 7τ, station No. 7
From then on, data is transmitted from station No. 8 at time 8τ. Similarly, in the second round, data is transmitted from station No. 2 at time 12τ, from station No. 7 at time 17τ, and in the third round, data is transmitted from station No. 2 at time 22τ.

According to this, since data transmission is performed by each station in a time-sharing manner, data collision does not occur even when data transmission is attempted from a plurality of stations.

In addition, each station has the station number to which it is transmitted and its own station has the assigned transmission order (in the above example, station number = transmission order).
Since the transmission timing is determined by itself based on the data, there is no need for centralized control by the master station.

Furthermore, if the data transmission time interval τ = Tc/N as in the above embodiment, each station can transmit data for each required value Tc of the real-time control response of all devices, so data can be transmitted without waiting time. I can do it.

〔Effect of the invention〕

As explained above, according to the present invention, the order of data transmission is assigned, and each station determines the timing to transmit data in this order based on identification information and transmits data, so that data transmission is performed in a time-sharing manner. management, and data collisions are prevented. Therefore, real-time performance can be maintained even for a large number of stations, and a large-scale LAN compatible with FA can be achieved.

Furthermore, since each station determines the timing at which it transmits data in a time-division manner by itself based on identification information, there is no need for centralized control by a master station, simplifying the entire system.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing one embodiment of this invention, with Figure 1 being a block diagram showing the overall configuration, Figure 2 being a diagram showing the configuration of each station, and Figure 3 showing an example of operation. It is a time chart. Figure 4 shows
1 is a block diagram showing a conventional device. 1 to N...station, 10...transmission line.

Claims (1)

[Claims] 1. A method for transmitting data from a plurality of stations via a common transmission path, in which each station transmits its own identification information when transmitting data, and each station Input the identification information from other stations, t=(i-j)τ (when i>j) {Tc-(j-i)}τ (when i<j), where t: own station's Data transmission time i: Local station number j: Receiving station number Tc: I/O request cycle for the entire system τ: Set the data transmission time t of the local station calculated from the data transmission time interval, and set the data transmission time t of the local station to this time t. The data transmission is characterized in that the station detects that the data has been reached and sends the data and identification information from its own station, and each station updates the set value of the data sending time t every time identification information is input from another station. Data transmission method.