JPH0547143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a transmission control method in a data transmission system composed of a plurality of programmable controllers connected in a loop.

[Conventional technology]

FIG. 4 is a schematic configuration diagram for explaining a transmission control method in a conventional data transmission system.
In the figure, reference numeral 11 indicates a master station consisting of a programmer controller, and reference numeral 12 indicates a slave station which also consists of a programmable controller and is connected to the master station 11 in a loop through a transmission path 13. Each slave station 12 receives messages. According to the transmission direction, 1, 2, 3...
Station numbers m, . . . n are assigned. Further, 14 is a line indicating the flow of messages from the master station 11, and 15 is a line indicating the flow of messages from the master station 11.
is a line showing the flow of messages from the slave station 12 with station number m.

Next, the operation will be explained. In the transmission control method of this data transmission system, data transmission is performed by a polling method, and FIG. 5 is a time chart showing the message transmission timing. As shown in FIG. 5, data transmission begins with the master station 11 sending a message. As shown by line 14 in FIG.
It is sent to the slave station 12 with station number 2, where it is received, relayed, and sent to the slave station 12 with station number 2. Thereafter, it is received and relayed in the same way, and from the slave station 12 of the last station number n to the master station 11.
It is returned to , and disappears here. The message format of the master station 11 is structured as shown in FIG. 6, for example. In the figure, 16 is a start flag, 17 is a transmission destination station number, 18 is transmission data, 1
9 is a frame check sequence, and 20 is an end flag. Each slave station 12 has the station number 17 of this transmission destination.
determine whether the message is addressed to its own station. The slave station 12 designated by the message from the master station 11 processes the received data and sends the message to the transmission path 13 accordingly.

Communication between the master station 11 and each slave station 12 is performed cyclically in order from the slave station 12 with station number 1 to the slave station 12 with station number n. This situation is shown by C in FIG. During this cyclic communication, slave station 1
The message sent from 2 is shown on line 15 in Figure 4.
As shown, the signal is received and relayed only by the child stations 12 with older numbers than the child station 12, and disappears when it reaches the master station 11 and is received. This cyclic communication ends when communication with the slave station 12 with station number n, which is the oldest number, is completed.
As shown in FIG. 5, the slave station 12 with the lowest station number 1
This process is repeated again from the beginning, thereby realizing data transmission.

[Problem that the invention seeks to solve]

Since the transmission control method of a conventional data transmission system using a programmable controller is configured as described above, a slave station can directly transmit data to a slave station with an older number than its own station. However, there was a problem in that data could not be directly transmitted to a slave station with a lower number than the own station, and the efficiency of data transmission between the slave stations deteriorated.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a transmission control system with high data transmission efficiency between slave stations.

[Means for solving problems]

In the transmission control system according to the present invention, when communication between slave stations becomes necessary, the master station performs communication between the slave stations at the break point of cyclic communication in response to a request from the slave station on the transmitting side. During this time period, the master station also relays messages sent from the oldest numbered slave station to the youngest numbered slave station.

[Effect]

The transmission control method of the present invention sets a time period for mutual communication between slave stations, and during this time period, messages received by the master station are relayed to the next slave station. Messages from slave stations can be received by all other stations.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 11 is a master station, 12 is a slave station, 13 is a transmission line, and 14 and 15 are lines showing the flow of messages from the master station 11 or slave station 12 in cyclic communication. 21 is a line showing the flow of messages for communication between slave stations.

Next, the operation will be explained. FIG. 2 is a time chart showing message transmission timing in this transmission control system. During the cyclic communication period indicated by C in the figure, processing proceeds in the same manner as in the conventional case. At this time, the message sent from the slave station 12 to the master station 11 includes a specific bit 22 indicating a request for communication between the slave stations 11. FIG. 3 is a format diagram showing an example of a message sent from the slave station 12 to the master station 11.

In the above-mentioned cyclic communication, the master station 11
When the slave station 12 specified by the message from the master station 12 needs to send data directly to another slave station 12, it sets the specific bit 22 of the message to be sent to the master station 11. When the master station 11 detects this set specific bit 22, after completing the communication with the last slave station in the cyclic communication, and before starting the next cyclic communication, the master station 11 sends the slave station indicated by T in FIG. A time slot for mutual communication is set, and the slave station 12 that sent the message with the aforementioned specific bit 22 set is caused to transmit the message. At this time, the message transmitted from the slave station 12 includes information such as the destination station number indicating which slave station 12 the message is addressed to.

As shown by line 21 in FIG. 1, the message sent from this slave station 12 is transmitted to
Even if it reaches the master station 11 from the slave station 12 and is received, it is not deleted, but is relayed from the master station 11 to the slave station 12 with the lowest station number 1, and is received and relayed by all the slave stations 12. , returns to the transmitting slave station 12 and disappears. During this time, the slave station 12 designated by the message processes the received data. When all of the above-mentioned processes in the time period for mutual communication between slave stations indicated by T in FIG. 2 are completed, the master station 11 resumes message transmission and returns to the process of cyclic communication. The above steps are repeated to realize data transmission including direct communication between slave stations.

〔Effect of the invention〕

As described above, according to the present invention, a time period is set for mutual communication between slave stations, and the master station is configured to relay messages to the next slave station during this time period, so that the message is not transmitted. A programmable controller that improves the efficiency of data transmission between slave stations because messages from a slave station are no longer deleted when they are received by the master station and can be received by all other stations. This has the effect of providing a transmission control method for a data transmission system configured with the following.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram for explaining a transmission control method in a data transmission system according to an embodiment of the present invention, Fig. 2 is a time chart showing the transmission timing of the message, and Fig. 3 is an example of the message. 4 is a schematic configuration diagram for explaining the transmission control method in a conventional data transmission system, FIG. 5 is a time chart showing the transmission timing of the message, and FIG. 6 is an example of the message. FIG. 11 is a master station, 12 is a slave station, 13 is a transmission path, 22
is specific information (specific bit) requesting communication between the slave stations, C is the period of cyclic communication, and T is the time period for communication between the slave stations.

Claims (1)

[Claims] 1 One programmable controller as a master station and a plurality of programmable controllers as slave stations are connected in a loop, and when cyclic communication is performed between the master station and slave stations, messages are connected in this loop. In a transmission control method, a message from the master station is sequentially received and relayed in a predetermined direction between the master station and the slave station, and the cyclic communication ends when the message reaches the master station. When the specified slave station needs to send data directly to another slave station, in order to prevent the message from disappearing until the message is returned to the slave station that sent the message,
The specified slave station sets and transmits specific information requesting communication between the slave stations in a message, and the master station that receives the message starts the next cyclic communication after the cyclic communication is completed. The main station is characterized in that a time period for mutual communication between the slave stations is set before the start of communication, and during this set time, the master station relays messages sent to the next slave station. Transmission control method.