JPH0993270A - Data transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data transmission system which starts quickly. SOLUTION: When a remote station 2 recognizes it that a master station 1 sends a CSMA/CD command, the remote station 2 judges it that the communication mode is the CSMA/CD mode. After taking a random standby time, an ID address allocated to its own station is sent. When collision on the transmission line 3 is detected, a random standby time is again taken and the ID address is sent. When no collision is detected, after the remote station 2 is in standby till the remote station 2 recognizes it that the master station 1 sends a polling/ selecting command, the remote station 2 makes usual transmission processing in the polling/selecting mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission system for transmitting data between a master station and a plurality of slave stations by a polling / selecting method.

[0002]

2. Description of the Related Art An example of the structure of such a data transmission system is shown in FIG. FIG. 4 shows a schematic configuration of a data transmission system, which is a master station 5 as a master station.
Are connected to a remote station 6 which is a plurality of slave stations by a transmission line 7 which is a twisted pair cable. The group of remote stations 6 constitutes a part of the control center 8. The master station 5 has a plurality of motor protection relays (none of which are shown) based on an instruction from the programmable controller.
Data is transmitted / received between the plurality of remote stations 6 connected to. The master station 5 has a transmission memory (not shown) therein, and a programmable controller is connected to the transmission memory in a writable and readable manner.

When the programmable controller of the master station 5 tries to obtain data from a plurality of remote stations 6 of the control center 8, the programmable controller writes the data in a predetermined area of the transmission memory to thereby obtain data from the master station 5. Then, the talker address (transmission request address) for the remote station 6 is output on the transmission path 7.

Then, among the remote stations 6, if it is determined that the talker address is the address assigned to itself, the data of the motor protection relay owned by itself is assigned to the master station 5. It outputs to the transmission path 7 together with the listening address (reception request address), and the master station 5 receives this data and writes it in the reception area of the transmission memory. Then, the programmable controller of the master station 5 reads this data from the transmission memory and performs processing based on the data. The above is so-called polling.

When controlling the drive of a motor (not shown) connected to each remote station 6, the programmable controller of the master station 5 gives the master station 5 a listener address (reception request address) for the remote station 6. It is output on the transmission line 7. Then, among the remote stations 6, the one that determines that the listener address is the address assigned to itself reads the control data added after the listener address, and according to the control data, Control motor stall. The above is selecting.

In such a polling / selecting system, for example, when polling n remote stations 6, the first remote station 6, the second remote station 6, ... Scanning is performed by sequentially transmitting talker addresses, and the data held by each remote station 6 is sequentially obtained.

Therefore, the master station 5 carries out initial polling at the time of system startup to check how many remote stations 6 are connected to the transmission line 7 (initial slave station connection detection). There is. In this initial polling, the master station 5 sequentially sends the talker addresses from the minimum to the maximum of the remote stations 6 connected to the transmission line 7, and determines that the remote station 6 that responded is connected. Is. Then, in subsequent scans in normal polling, the master station 5 sends only the talker address of the connected remote station 6.

[0008]

However, in this initial polling, regardless of the number of remote stations 6 actually connected to the transmission line 7, the master station 5 always gives the talker address from the minimum to the maximum. Since the control center 8 as a system is started up slowly, the operation cannot be started immediately because the control center 8 as a system is delayed because the control center 8 is sent out sequentially and a response is waited for a fixed time each time.

The present invention solves the above problems, and an object thereof is to provide a data transmission system in which a master station can quickly detect whether or not each slave station is connected to a transmission path.

[0010]

In order to achieve the above object, a data transmission system according to a first aspect of the present invention is a data transmission system in which a master station and a plurality of slave stations are connected via a transmission path, and data is polled / selecting. In the transmission,
When the master station detects the initial slave station connection detection when the master station checks whether there is a connection to the transmission path of each slave station at startup, the master station detects the CSMA / CD
Issue a command to change the communication mode of the transmission line to CSMA / C
This is performed by setting the D mode and receiving the address transmitted by each slave station.

In this case, when the master station sets the communication mode of the transmission path to the CSMA / CD mode, it is said that the transmission of the addresses of all the slave stations is completed when the transmission of the addresses from the slave stations is not performed for a certain time or more. Alternatively, the polling / selecting command may be issued to switch the communication mode of the transmission path to the polling / selecting mode (claim 2).

Further, the slave station has a communication mode of CS on the transmission line.
In MA / CD mode, the master station completes transmission of its own address and then the master station polls / selects.
You may make it hold | maintain on standby until a command is issued (Claim 3).

Further, even when the communication mode of the transmission path is the polling / selecting mode, the master station performs the same process as the initial slave station connection detection every time each slave station is scanned once in polling. It may be carried out as the intermediate station connection detection (Claim 4).

Furthermore, when the communication mode of the transmission path is the polling / selecting mode, the master station
1 every time each slave station is scanned multiple times during polling
The same process as the initial slave station connection detection may be performed as the intermediate slave station connection detection (claim 5).

In addition, when the slave station is connected to the transmission line while the system is operating and issues a slave station connection detection request command to the master station, the master station performs the same processing as the initial slave station connection detection. May be performed as the intermediate station connection detection (claim 6).

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 3 shows a schematic configuration of a data transmission system. A master station 1 which is a master station is connected to a remote station 2 which is a plurality of slave stations by a transmission line 3 which is a twisted pair cable. The remote station 2 group constitutes a part of the control center 4. The master station 1 transmits / receives data between a plurality of remote stations 2 connected to a plurality of motor protection relays (none of which is shown) based on an instruction from the programmable controller. The master station 1 has a transmission memory (not shown) therein, and a programmable controller is connected to the transmission memory in a writable and readable manner.

The configuration of this embodiment is substantially the same as that of the conventional one shown in FIG. 4, and different operations will be described below with reference to FIGS. 1 and 2. In FIG. 1, which shows a flow chart of the control contents inside the remote station 2, when the control center 4 is activated, each remote station 2 firstly, in the processing step S1 of "CSMA / CD command transmission?" It is determined by 1 whether or not the CSMA / CD command is transmitted (issued) on the transmission path 3. When the CSMA / CD command is not transmitted and it is determined to be "NO", the process proceeds to step S6 of the "normal transmission process" to execute a normal transmission process routine as will be described later, and then to step S1.

On the other hand, in step S1, when the CSMA / CD command is transmitted from the master station 1 onto the transmission line 3 and it is determined to be "YES" (see FIG. 2A), each remote station 2 has the transmission line 3 connected. It is determined that the communication mode has shifted to the CSMA / CD mode. This CSMA / CD mode is Ethernet (ETHERNET)
CSMA / CD (Carrier Sence Mu
ltiple Access with Collision Detection) It is similar to the communication method. And each remote station 2
Shifts to the processing step S2 of "random delay processing".

In processing step S2, each remote station 2 takes a random waiting time according to a random number given by an internal random number generator or the like, and then proceeds to processing step S3 of "address transmission". Transition. In processing step S3, each remote station 2 confirms that no carrier (carrier signal) for data transmission is detected on the transmission path 3, and then masters the ID address (address) assigned to itself. It is transmitted to the station 1 (see FIG. 2 (c)). Then, the process proceeds to the judgment step S4 of "collision detected?".

In the determination step S4, each remote station 2 monitors the state of the transmission path 3 and, as a result of transmitting the ID address of its own station in step S3, a collision (Collision) occurs on the transmission path 3. Judge whether or not. This collision means that there is a time lag in transmitting the transmission data on the transmission path 3, so after confirming that no carrier is detected, even if one remote station 2 transmits, another remote station Two
May simultaneously perform transmission, resulting in collision of transmission data.

If a collision is detected at a certain remote station 2 and if "YES" is determined in the determination step S4, the process proceeds to steps S2 and S3, and the ID address is retransmitted after taking a random waiting time again. Then, until no collision is detected in step S4, the ID address is normally transmitted, and the determination is “NO”,
The loop of steps S2 to S4 is repeated.

If a collision is not detected and it is judged "NO" in the judgment step S4, the process proceeds to a judgment step S5 of "polling / selecting command transmitted?". In the determination step S5, the remote station 2 waits until the master station 1 transmits a polling / selecting command on the transmission path 3. The master station 1 monitors the transmission time interval of the ID address randomly transmitted by the remote station 2. Immediately after issuing the CSMA / CD command, the transmission time interval of the ID address is short, but as each remote station 2 gradually completes the transmission of the ID address, the transmission time interval gradually becomes longer. Then, when the transmission time interval becomes equal to or longer than the predetermined time, it can be determined that all the remote stations 2 have completed the transmission of the ID address.

When the master station 1 determines that all the remote stations 2 have completed the transmission of the ID address, the master station 1 transmits a polling / selecting command on the transmission line 3 (see FIG. 2 (a)). ). Then, each remote station 2 judges "YES" in the judgment step S5 and recognizes that the communication mode of the transmission line 3 has shifted to the polling / selecting mode (the CSMA / CD mode is released). ), And proceeds to step S6 to perform normal transmission processing. The above processing is performed as the initial slave station connection detection, and the master station 1
Can detect how many remote stations 2 are connected on the transmission path 3.

Process step S6 is a normal transmission process in the polling / selecting mode. The remote station 2 waits for the listener or talker address to be transmitted from the master station 1, and when the talker address is transmitted, the remote station 2 starts the motor according to the attached control command. After that, the master station 1 performs a scanning operation to sequentially transmit the talker address of each remote station 2 which is confirmed to be connected in the initial slave station connection detection, and relates to the motor held by each remote station 2. The operation state of the motor is monitored by periodically obtaining various data, and the operation of the motor is controlled if necessary.

When the normal transmission processing routine as described above is completed, the process moves to step S1 and the remote station 2 restarts from the master station 1 to the CSMA / C.
It is periodically checked whether or not the D command is transmitted, and if not transmitted, the process proceeds to step S6.

As described above, according to this embodiment, the master station 1 detects the initial slave station connection at the time of starting the CSM.
Issue the A / CD command and set the communication mode of transmission line 3 to C
Each remote station 2 in SMA / CD mode
Since it is performed by receiving the ID address transmitted by, unlike the prior art, it can be performed promptly without needing a useless waiting time, and can be promptly started up to start the operation.

Further, according to this embodiment, when the master station 1 sets the communication mode of the transmission line 3 to the CSMA / CD mode, when the ID address is not transmitted from the remote station 2 for a certain time or longer, It is judged that the transmission of the ID addresses from all the remote stations 2 is completed, and the polling / selecting command is transmitted to switch the communication mode of the transmission line 3 to the polling / selecting mode. The communication mode can be switched quickly.

Further, according to the present embodiment, when the communication mode of the transmission line 3 is the CSMA / CD mode, the remote station 2 completes the transmission of its own ID address and then the master station 1 Since the standby state is held until the polling / selecting command is transmitted, it is possible to quickly respond to the switching of the communication mode of the transmission path 3.

The present invention is not limited to the embodiments described above and shown in the drawings, but the following modifications and expansions are possible. The master station 1 has a transmission line 3
Even when the communication mode is the polling / selecting mode, the processing similar to the initial slave station connection detection may be performed as the intermediate slave station connection detection every time each remote station 2 is scanned in the polling. By doing so, it is possible to detect the remote station 2 connected to or disconnected from the transmission line 3 after the data transmission system is activated.

Further, this intermediate station connection detection may be performed once every time each remote station 2 is scanned a plurality of times in polling. By doing so, the transmission efficiency of the data transmission system can be improved.

When the remote station 2 is connected to the transmission line 3 after being activated, the slave station connection detection request command is transmitted from the connected remote station 2 to the master station 1 so that the master station 1
May detect the intermediate slave station connection when the slave station connection detection request command is received. According to this structure, the transmission efficiency of the data transmission system can be further improved.

When the communication mode of the transmission path 3 becomes the CSMA / CD mode, the remote station 2 transmits the ID address assigned to itself, but the talker address or listener assigned to itself is transmitted. You may send the address. Not limited to the control center 4, any data transmission system can be applied as long as it is a data transmission system that connects a master station and a plurality of slave stations via a transmission path.

[0033]

Since the present invention is as described above,
The following effects are obtained. According to the data transmission system of claim 1, the master station issues a CSMA / CD command at startup, sets the communication mode of the transmission path to CSMA / CD mode, and receives the address transmitted by each slave station. Since the presence or absence of connection to the transmission path of each slave station is checked by, unlike the conventional method, it is possible to quickly detect the presence or absence of the connection of each slave station to the transmission path without needing unnecessary waiting time. The system can be started up quickly and put into operation.

According to the data transmission system of the second aspect, when the master station sets the communication mode of the transmission path to the CSMA / CD mode, when all addresses are not transmitted from the slave station for a certain time or longer, all the slave stations Since it is judged that the transmission of the station address is completed and the communication mode of the transmission path is switched to the polling / selecting mode, the communication mode can be switched quickly.

According to the data transmission system of the third aspect, when the communication mode of the transmission path becomes the CSMA / CD mode, the slave station polls the master station after completing transmission of its own address. / Held in a standby state until a selecting command is issued.

According to the data transmission system of the fourth aspect, even when the communication mode of the transmission path is the polling / selecting mode, the master station has an intermediate node each time each slave station is scanned once in polling. Since the station connection is detected, it is possible to detect a slave station that is connected to the transmission path or has left the transmission path after the system is activated.

According to the data transmission system of the fifth aspect, even if the communication mode of the transmission path is the polling / selecting mode, the master station makes 1 every time each slave station scans a plurality of times in polling. Since the intermediate slave station connection is detected, the transmission efficiency can be improved.

According to the data transmission system of the sixth aspect, the master station is connected to the transmission path while the slave station is operating, and when the slave station issues a slave station connection detection request command to the master station, Since the station connection is detected, the transmission efficiency can be further improved.

[Brief description of drawings]

FIG. 1 is a flowchart of control contents of a remote station showing an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing data transmission of a control center.

FIG. 3 is a block diagram of a data transmission system

FIG. 4 is a view corresponding to FIG. 3 showing a conventional technique.

[Explanation of symbols]

Reference numeral 1 is a master station (master station), 2 is a remote station (slave station), 3 is a transmission line, and 4 is a control center (data transmission system).

Claims (6)

[Claims] 1. In a data transmission system in which a master station and a plurality of slave stations are connected via a transmission path and data is transmitted by a polling / selecting method, the master station connects to the transmission path of each slave station at startup. The parent station detects the initial slave station connection detection that checks for the presence of
Issue a command to change the communication mode of the transmission line to CSMA / C
Data transmission system characterized by performing in D mode by receiving an address transmitted by each slave station 2. The master station sets the communication mode of the transmission path to CSMA.
In the / CD mode, if the addresses from the slave stations are not transmitted for a certain period of time or more, it is determined that the addresses of all the slave stations have been transmitted, and a polling / selecting command is issued to send the transmission path. 2. The data transmission system according to claim 1, wherein the communication mode is switched to a polling / selecting mode. 3. The slave station has a transmission line communication mode of CSMA.
3. The data according to claim 2, wherein in the / CD mode, after the transmission of the address of the own station is completed, the master station is kept in a standby state until it issues a polling / selecting command. Transmission system. 4. The master station performs the same processing as the initial slave station connection detection every time each slave station is scanned once in polling even when the communication mode of the transmission path is the polling / selecting mode. The data transmission system according to any one of claims 1 to 3, wherein the data transmission system is performed as an intermediate station connection detection. 5. The master station, even when the communication mode of the transmission path is the polling / selecting mode, is the same as the initial slave station connection detection once every time each slave station is scanned multiple times in polling. The data transmission system according to any one of claims 1 to 3, wherein the processing is performed as an intermediate slave station connection detection. 6. The master station performs the same process as the initial slave station connection detection when the slave station is connected to the transmission line while the system is operating and issues a slave station connection detection request command to the master station. The data transmission system according to any one of claims 1 to 3, wherein the data transmission system is performed as an intermediate station connection detection.