JP2004328278A - Communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the noise of a line of a communication system which has a master station and slave stations connected by busses. <P>SOLUTION: A branch line switch 16 is provided between a branch point 15 from a transmission line L2 to each slave station and a transceiver 18, and a trunk line switch 20 is provided between the branch point 15 and an output part 12 to the next slave station, and only a slave station which will transmit data sets the branch line switch 16 to a conductive state to connect to a trunk line and sets the trunk line switch 20 to an open state to disconnect slave stations being father from the master station than the slave station itself, from the trunk line. A slave station which will not transmit data, sets the branch line switch 16 to an open state to disconnect the slave station itself from the trunk line and sets the trunk line switch to a conductive state to be set to such a state that transmission data from another slave station can be transmitted. Since such a state is equivalently set that lines unnecessary for data transmission between a slave station transmitting data and the master station are removed, an influence of the impedance or the like of removed parts is eliminated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides, for example, a servo amplifier control device for performing servo motor control and spindle motor control, or a plurality of slave stations including a spindle amplifier control device and a master station including a numerical control device via a serial transmission line. The present invention relates to a communication system which is connected and performs data transmission between the two.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a communication system including a plurality of slave stations and a master station controlling the slave stations, for example, the slave station and the master station are connected by a bus line for a half-duplex serial transmission. There has been proposed a communication system for performing the above. For example, FIG. 7 shows a communication system connected by a bus line for serial transmission of a half-duplex system called a multi-drop system, and the bus lines include stations 1 to n as master stations and slave stations. The stations 1 and n at both ends are connected and require terminating resistors 51 and 52.
[0003]
For example, when data is transmitted from the station 2 to the station 1, the terminating resistors 51 and 52 transmit data also to the station n. Reflection occurs, which causes transmission errors and the like, and is provided to avoid this. In FIG. 7, reference numeral 53 denotes a receiver, 54 denotes a transceiver, and 55 denotes an internal circuit, and each station has the same configuration.
As a method for connecting a master station and a slave station, as shown in FIG. 8, a method for connecting by a full-duplex serial transmission line has been proposed.
[0004]
Even in a communication system connected by a full-duplex serial transmission line, for example, when the slave station S2 transmits to the master station M, the data is also transmitted to the slave station Sn. The terminating resistors 61 and 62 are required in the slave station Sn that terminates, and the terminating resistors 66 and 67 are also required in the master station M. In FIG. 8, each slave station includes a transceiver 63, a receiver 64, and an internal circuit 65. Only the slave station Sn serving as a termination is further configured to include the termination resistors 61 and 62 as described above. You. Similarly, the master station M also includes a transceiver 68, a receiver 69, and an internal circuit 70, and further includes the terminating resistors 66 and 67 as described above.
[0005]
As a communication system that is connected by a full-duplex serial transmission line, a connection method as shown in FIG. 9 has also been proposed.
In FIG. 9, each slave station has a connection unit 71 for connecting a line from a previous station, that is, a station located on the master side, and a connection unit 72 for connecting a line to a subsequent station. , And slave stations are connected serially. This connection method is a connection method called a serial multi-drop method, and also in this case, the last station (slave station S3 in FIG. 9) requires terminating resistors 73 and 74. Each slave station has the same configuration, 75 is a receiver, 76 is a transceiver, and 77 is an internal circuit. Also, the master station M is configured to include the terminating resistors 66 and 67, the transceiver 68, the receiver 69, and the internal circuit 70 as in FIG.
[0006]
Also, as shown in FIG. 10, terminating resistors 81 and 82 are mounted for each slave station, and the terminating resistors 81 and 82 are enabled or disabled by a switch means 83, and whether or not the slave station is the final slave station is determined. A connection method in which slave stations are connected without being conscious has been proposed. In FIG. 10, each slave station has the same configuration, and includes the terminating resistors 81 and 82, switch means 83, receiver 84, transceiver 85, and internal circuit 86, respectively. The master station M is configured in the same manner as in FIGS.
[0007]
When multiple stations are connected by such a multi-drop method, not only the effect of longer cable length but also the effect of branched branch lines are added, which causes reflection noise and noise effects. More easily.
In order to avoid this, the first arrival of signals in two transmission routes, which are signals from a trunk line for connecting a master station and a slave station and a branch line for connecting a transceiver or a receiver of the slave station, is detected, and By enabling one of the two transmission routes and disabling the other according to the detection result, it is possible to prevent signal sneak, to ensure reliable signal transmission in bidirectional communication, and to facilitate impedance matching. (Patent Literature 1), or a method of removing the influence of a branch line by setting the length of the branch line at a specific ratio (Patent Document 2). Etc. have been proposed.
[0008]
[Patent Document 1]
Patent No. 3054318
[Patent Document 2]
JP 2001-333115 A
[0009]
[Problems to be solved by the invention]
However, as described above, in a communication system in which a plurality of slave stations are connected to the master station by the multi-drop method, data is transmitted not only to the line to the master station but also to the lines and branch lines of all slave stations. Is transmitted, it is easily affected by a branch line or a transceiver, and particularly easily affected by noise due to a longer cable. For this reason, the circuit scale is increased, for example, it is necessary to add a circuit for adjusting the impedance so that the termination can be performed properly, or to add a component for increasing noise resistance.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a communication system that is resistant to noise while suppressing an increase in circuit scale and reducing noise due to the influence of a line connecting slaves or a branch line.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a communication system according to claim 1 of the present invention has a master station and a slave station connected by a bus, and each station has a line through which the slave station transmits data to the master station. In a communication system in which a plurality of stations are used at a timing not used at the same time, the slave station is inserted into a branch line between the slave station and a branch point of the line to which the slave station is connected, and the slave station is connected to the branch station. Branch line disconnecting means for disconnecting from the line, and a slave station provided between each branch point of the line corresponding to each slave station and located farther from the master station with respect to the slave station; Main line cutoff means for disconnecting the data from any of the branch line cutoff means when any of the slave stations performs data transmission to the master station. Only the branch line disconnecting means that can connect a slave station that performs transmission to the line is in a conductive state, and is located adjacent to a branch point to which the slave station that performs data transmission is connected and farther from the master station. It is characterized in that the main line blocking means is set in an open state.
[0011]
Further, in the communication system according to claim 2, the master station and the slave station are bus-connected in a full-duplex manner, the slave station receiving the transmission frame from the master station transmits a response frame to the master station, and In a communication system in which a master station transmits the transmission frame at a timing at which a response frame is not received from a plurality of slave stations at the same time, the slave station is connected to the slave station and the line to which the slave station is connected. A branch line intercepting means inserted into a branch line between the branch station and the branch station for disconnecting the slave station from the line, and located on a side farther from the master station with reference to a branch point to which the slave station is connected; Main line cutoff means for disconnecting the slave station from the line, wherein the slave station transmits a response frame addressed to the master station. When the data is not transmitted to the master station, the branch line disconnecting means is opened and the trunk line disconnecting means is turned on when the data transmission to the master station is not performed. It is characterized in that it is in a state.
Further, the communication system according to claim 3 is characterized in that the master station is a terminal station.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described.
FIG. 1 is a schematic configuration diagram showing a configuration of a communication system to which the first embodiment of the present invention has been applied.
As shown in FIG. 1, the communication system 100 includes a master station M, and three slave stations S1 to S3 connected to the master station M by a full-duplex serial transmission line. Then, the master station M transmits a transmission frame to the slave station, and the slave station receiving the transmission frame addressed to the own station transmits a response frame to the master station M. Further, the master station M adjusts the transmission timing of the transmission frame so that the transmission frame is not transmitted from a plurality of slave stations at the same time.
[0013]
When each of the slave stations has its own station, m, the connection section 11 between the preceding station (m−1), that is, the slave station closer to the master station M or the previous stage that can be connected to the master station, And a connection unit 12 with the next stage that can be connected to the station (m + 1) of the stage, that is, a station far from the master station M. The connection units 11 and 12 with the previous and next stages are connected to the master station M. It is provided independently for data transmission and for data transmission from the master station. The transmission line L1 for transmitting data from the master station M is connected from the master station M or the preceding slave station to the receiver 14 of the slave station via the connection section 11 and the branch point 13 in the slave station. At the same time, it is connected from the branch point 13 to the connection unit 12 with the next stage, and is connected via the connection unit 12 to the next-stage slave station.
[0014]
A transmission line L2 for transmitting data to the master station M is connected to the slave station transceiver 18 from the master station M or the preceding slave station via the connecting portion 11, the branch point 15 in the slave station, and the branch line switch 16. , And from the branch point 15 via the trunk switch 20 to the connection unit 12 with the next stage, and via the connection unit 12 to the next-stage slave station.
[0015]
Then, resistors R1 and R2 are connected to the connection section 12 of the last-stage slave station, and constitute the terminating resistors of the transmission lines L1 and L2, respectively.
The branch line switch 16 and the trunk line switch 20 are on / off controlled by a switch switching circuit 30 provided in each slave station so as to be opposite to each other. The switch switching circuit 30 controls the branch line switch 16 and the trunk line switch 20 based on a transmission enable set by the internal circuit 10 of the slave station according to whether or not the own station is in a state capable of performing data transmission. Is switched.
[0016]
Here, in the slave station, when data transmission is performed from the slave station, transmission is enabled from the transceiver 18 with transmission enable enabled (HIGH). On the other hand, when the transmission enable is invalid, the transmission data becomes high impedance. The switch switching circuit 30 turns on the branch switch 16 when the transmission enable is valid, and turns on the trunk switch 20 when the transmission enable is invalid. Therefore, when the transmission enable is valid, the branch switch 16 is turned on, the transceiver 18 is connected to the connection section 11 with the preceding stage, and the transmission data of the transceiver 18 can be transmitted to the preceding stage. Since it is in the OFF state, the transmission data of the transceiver 18 cannot be transmitted to the next stage. On the other hand, when the transmission enable is invalid, the branch line switch 16 is turned off, the transceiver 18 is disconnected from the connection 11 between the previous stage, and the connection 11 between the previous stage and the connection 12 between the next stage are connected. Thus, the transmission data from the next stage can be transmitted to the previous stage.
[0017]
The receiver 14 and the transceiver 18 are connected to an internal circuit 10. The internal circuit 10 receives transmission data from the master station M via the receiver 14, and generates response data based on the received transmission data. Is transmitted via the transceiver 18.
On the other hand, the master station M includes an internal circuit 51, and a transceiver 52 for transmitting transmission data from the internal circuit 51 is connected to a transmission connection unit 54, and the transmission connection unit 54 By connecting to the line L1, data is transmitted from the master station M to the slave station S1. In addition, a receiver 55 for receiving transmission data from the slave station S1 and transmitting the transmission data to the internal circuit 51 is connected to the reception connection unit 57, and the reception connection unit 57 is connected to the transmission line L2. Thereby, the transmission data from the slave station S1 is transmitted to the master station M. Terminating resistors 53 and 56 are connected between the transmitting connection 54 and the transceiver 52 and between the receiving connection 57 and the receiver 55, respectively.
[0018]
Then, the internal circuit 51 issues a transmission request of transmission data or control status data including parameters for controlling a device to be controlled of each slave station to any slave station at a predetermined timing set in advance. The transmission data to be transmitted is transmitted, and response data is received from each slave station as a response. Further, the master station M transmits the transmission frame to the next slave station after the reception of the transmission frame from the slave station is completed.
[0019]
Further, when receiving the transmission data addressed to the own station from the master station M, the slave station generates a response frame according to the instruction in the transmission frame, and transmits the response frame to the master station M.
Next, the operation of the first embodiment will be described.
Now, as shown in FIG. 2, it is assumed that the master station M sequentially transmits a transmission frame in the order of the slave stations S1, S2, and S3, and receives a transmission frame as a response from each of the slave stations S1 to S3. .
[0020]
2A shows the timing at which the master station M transmits a transmission frame to the slave station, FIG. 2B shows the timing at which the slave station transmits a transmission frame to the master station M, and FIG. (D) shows the state of the trunk switch 20 of the slave station S1, (e) shows the state of the branch switch 16 of the slave station S1, (f) shows the state of the transmission enable of the slave station S2, and (g) shows the state of the transmission enable of the slave station S2. The state of the trunk switch 20 of the slave station S2, (h) the state of the branch switch 16 of the slave station S2, (i) the transmission enable state of the slave station S3, and (j) the state of the trunk switch 20 of the slave station S3. , (K) indicate the state of the branch switch 16 of the slave station S3.
[0021]
When the internal circuit 51 of the master station M transmits transmission data addressed to the slave station S1 at time t1, the transmission data is transmitted to the slave station S1 via the transceiver 52 and the connection unit 54 via the transmission line L1. The signal is transmitted to the connection unit 11, and is transmitted to the internal circuit 10 via the receiver 14 via the branch point 13. Further, the transmission frame is transmitted from the branch point 13 to the next-stage slave station S2 via the connection unit 12, and the transmission frame is similarly transmitted to the internal circuit 10 at the slave station S2. The signal is transmitted to the slave station S3 at the next stage, and is similarly transmitted to the internal circuit 10 at the slave station S3. Then, the data is transmitted from the branching point 13 to the next stage via the next-stage connection unit 12. Since the terminating resistor R1 is connected, the data transmission to the next stage ends at the terminating resistor R1.
[0022]
Each of the slave stations S1 to S3 determines whether or not the received transmission frame is a transmission frame addressed to the own station. Since the slave stations S2 and S3 are not transmission frames addressed to the own station, the received transmission frame is not determined. Is not performed.
On the other hand, the slave station S1 generates a transmission frame addressed to the master station M as a response to the transmission frame because the transmission frame is addressed to the own station, and transmits the transmission frame at time t2 with the transmission enable being HIGH.
[0023]
Here, in the slave station S1, since the communication enable is HIGH, the switch switching circuit 30 switches the trunk line switch 20 off and the branch line switch 16 on.
Thereby, as shown in FIG. 3, the internal circuit 10, the transceiver 18, the branch line switch 16, and the connection unit 11 on the slave station S1 side, and the reception side connection unit 57, the receiver 55, and the internal circuit 51 on the master station M side. Since the conduction state is established, the transmission data from the slave station S1 can be transmitted to the master station M. On the other hand, since the main switch 20 is turned off, the transmission path to the slave station S2 is cut off, that is, the transmission line L2 connecting the master station M and each of the slave stations S1 to S3 is cut off by the slave station S1. It will be in the state that was done. Therefore, the transmission line L2 after the slave station 1 is removed, that is, the cable length is shortened accordingly, so that noise can be reduced accordingly.
[0024]
Further, since the slave stations S2 and S3 do not transmit transmission data, the trunk line switch 20 is turned on and the branch line switch 16 is turned off. However, since the trunk line is cut off at the slave station S1, transmission to the next stage is performed. No data is transmitted.
Therefore, the transmission data transmitted by the slave station S1 is transmitted only to the master station M without being transmitted to the other slave stations S2 and S3, that is, between the master station M and the slave station S1. Thus, the state becomes equivalent to the case where one-to-one communication is performed, and the cable length is the shortest cable length necessary for performing communication between the master station M and the slave station S1. Therefore, it is possible to suppress the occurrence of noise caused by a part unnecessary for communication.
[0025]
Next, at time t3, the transmission of the transmission frame from the slave station S1 ends, and when the transmission enable becomes LOW, the trunk line switch 20 is turned on and the branch line switch 16 is turned off. Therefore, the trunk switch 20 in each of the slave stations S1 to S3 is turned on, so that the trunk between the master station M and each of the slave stations S1 to S3 is connected, and the transmission from each of the slave stations S1 to S3 is performed. The frame can be transmitted to the master station M.
[0026]
Then, at time t3, the transmission of the transmission frame from the slave station S1 ends, and the master station M transmits a transmission frame to the slave station S2 in response to the transmission frame, and the transmission frame is transmitted to each of the slave stations S1 to S3. However, since this transmission frame is a transmission frame addressed to the slave station S2, the slave station S2 sets the transmission enable to HIGH and transmits a transmission frame addressed to the master station M at time t4 as a response to the transmission frame.
[0027]
At this time, in the slave station S2, since the transmission enable is HIGH, the switch switching circuit 30 switches the branch line switch 16 on and the trunk line switch 20 off as shown in FIG.
As a result, in the slave station S2, the internal circuit 10, the transceiver 18, the branch line switch 16, and the connection 11 with the preceding stage are in a conductive state, and the transmission data from the internal circuit 10 of the slave station S2 can be transmitted to the slave station S1. It becomes a state. On the other hand, since the trunk switch 20 is off, the transmission line L2 is disconnected between the slave station S2 and the slave station S3.
[0028]
On the other hand, in the slave stations S1 and S3, since the transmission enable is off, the trunk switch 20 is turned on and the branch switch 16 is turned off. Here, the trunk line between the slave stations S2 and S3 is cut off by the slave station S2 because the trunk switch 20 of the slave station S3 is off, but the trunk switch 20 of the slave station S1 is on. The trunk line between the slave stations S1 and S2 is in a connected state.
[0029]
Therefore, the transmission data from the slave station S2 is transmitted from the slave station S2 to the master station M via the slave station S1, but in this case, the transceiver 18 is disconnected from the transmission line L2 in the slave station S1. It is in a state. Therefore, a state equivalent to the case where one-to-one communication is performed between the master station M and the slave station S2, that is, a cable having a cable length necessary for communication between the master station M and the slave station S2 and between them. Only the connected cables are connected, and unnecessary cable portions and unnecessary slave stations are removed from the communication between them. This can remove noise that occurs.
[0030]
Next, at time t5, when the transmission of the transmission data in the slave station S2 ends and the transmission enable becomes LOW, in the slave station S2, the trunk line switch 20 is turned on, the branch line switch 16 is turned off, and the slave stations S1 to S3 switch to the master station. Data transmission to the station M is enabled.
Subsequently, when the master station M transmits a transmission frame to the slave station S3, and at time t6, the slave station S3 sets the transmission enable to HIGH and transmits the transmission frame to the master station M, as shown in FIG. Since the transmission enable is HIGH in the slave station S3, the branch switch 16 is turned on and the trunk switch 20 is turned off. In the slave stations S1 and S2, the transmission enable is LOW, so that the branch switch is turned off. 16 is off, and the trunk switch 20 is kept on.
[0031]
Therefore, as shown in FIG. 5, the transmission frame generated by the internal circuit 10 of the slave station S3 is transmitted from the slave station S3 to the master station M via the slave station S2 and the slave station S1. In the slave stations S1 and S2, the branch line switch 16 is turned off, so that the master station M and the slave station S3 are connected by the shortest cable length and are in the same state as when one-to-one communication is performed. It becomes.
[0032]
Then, at time t7, when the transmission of the transmission frame in the slave station S3 is completed and the transmission enable becomes LOW, the branch line switch 16 is turned off and the trunk line switch 20 is turned on, and the slave stations S1 to S3 to the master station M. Is connected.
As described above, in each slave station, the branch line switch 16 for disconnecting the transceiver 18 from the transmission line L2 and the trunk line switch 20 for disconnecting between the own station and the next-stage slave station are provided. When transmitting a frame, the trunk switch 20 of the own station is turned off, the slave station at the next stage is cut off from the trunk, and the branch switch 16 is turned off at the other slave stations, and the transceiver 18 and the transmission line L2 are connected. I try to cut off.
[0033]
Therefore, when data transmission is performed from the slave station to the master station, a state equivalent to the case where one-to-one communication is performed between the master station M and the slave station is formed, and data transmission to the master station is performed. Only the shortest line connecting the master station and the slave station is connected.By disconnecting the transmission line to which the subsequent slave station is connected, the transmission frame is transmitted to the subsequent slave station that is not related to communication, and is affected by reflected noise. Can be prevented, and the transceiver of the slave station existing between the slave station transmitting the transmission frame addressed to the master station M and the master station is disconnected from the trunk line, so that the slave in the next stage can be shifted. Reduces noise due to the influence of transmission lines to and from branch stations and the impedance of transceivers, and is in a state equivalent to one-to-one communication In other words, so that the state is not affected by the other stations.
[0034]
For this reason, a communication system resistant to noise can be obtained, and a system resistant to noise can be obtained in this manner. A circuit or the like for adjusting the size of the circuit becomes unnecessary, and the circuit scale can be reduced.
In the first embodiment, a case has been described where an external terminating resistor R2 is connected as a terminating terminal on the transmission line L2 from the slave station to the master station. It is not necessary to connect.
[0035]
However, by providing the terminating resistor R2, for example, the branch switch 16 and the trunk switch 20 of each slave station are all brought into a conductive state, so that the operation is performed as a multi-drop system shown in FIG. Is also possible.
Further, by making the branch switch 16 and the trunk switch 20 conductive, it is possible to perform the same operation as a slave station having no branch switch 16 and the trunk switch 20 shown in FIG. It is also possible to configure a communication system in which a slave station having the branch line switch 16 and the trunk line switch 20 shown in FIG. 9 and a slave station having no branch line switch 16 and the trunk line switch 20 shown in FIG. 9 are mixed. Even when a communication system is configured by mixing different types of slave stations, a system can be easily constructed by operating the branch line switch 16 and the trunk line switch 20. In this case, since the system is operated as a multi-drop communication system, it is necessary to provide an external terminating resistor R2.
[0036]
Next, a second embodiment of the present invention will be described.
The second embodiment is an example applied to a communication system in which a terminating resistor is mounted on each slave station as shown in FIG. The same parts as those in the communication system according to the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0037]
The communication system 100 according to the second embodiment is different from the communication system shown in FIG. 1 in that terminal resistors R11 and R12 are provided in each slave station instead of the terminal resistors R1 and R2 as shown in FIG. Have been. The terminating resistor R11 is connected via a terminating switch 23 to a branch point 21 between the branch point 13 and the connection part 12 to the next stage. The terminating resistor R12 is connected via a terminating switch 27 to a branch point 25 between the trunk switch 20 and the connection section 12 to the next stage.
[0038]
These termination switches 23 and 27 are switched according to whether or not they are the last-stage slave stations, for example, by setting manually by an operator. Specifically, the termination switches 23 and 27 are controlled to be ON only in the last-stage slave station, and the termination switches 23 and 27 are controlled to be OFF in slave stations other than the final-stage slave station. , The terminating resistor is made effective.
[0039]
The branch line switch 16 and the trunk line switch 20 are switched in accordance with the transmission enable, as in the first embodiment.
Therefore, also in the second embodiment, the same operation and effect as those of the first embodiment can be obtained, and in the second embodiment, a terminating resistor is mounted on each slave station. Since this can be set to be valid or invalid in each slave station, there is no need to consider which slave station is to be the last-stage slave station, and there is no restriction on the slave stations in the communication system, It can be connected to any position.
[0040]
Also in the second embodiment, when the transmission frame is transmitted from the slave station to the master station M by switching the branch line switch 16 and the trunk line switch 20, the state is equivalent to the one-to-one communication. Therefore, it is not always necessary to provide a terminating resistor on the transmission line L2 side.
However, also in this case, by providing the terminating resistor, a communication system in which a slave station having no branch switch 16 and the trunk switch 20 shown in FIG. 9 and a slave station having the branch switch 16 and the trunk switch 20 are mixed. In this case, by setting the branch line switch 16 and the trunk line switch 20 to the conductive state, a normal multi-drop communication system can be easily configured.
[0041]
In each of the above embodiments, the case where the terminating resistor is provided as the terminating point is described. However, the present invention is not limited to this, and a terminating circuit can be applied.
In each of the above embodiments, a case has been described in which a communication system is configured with one master station and three slave stations. However, the present invention can be applied to a communication system including an arbitrary number of slave stations. Needless to say.
[0042]
Further, in each of the above-described embodiments, the case has been described where the slave station transmits the transmission frame to the master station M when the transmission frame is received from the master station M. However, the present invention is not limited to this. The present invention can be applied to any transmission system in which a plurality of slave stations do not transmit a transmission frame at the same time, and if such a transmission system is used, it is applied to a half-duplex serial multi-drop communication system. It is also possible.
[0043]
Further, in each of the above embodiments, the case where the present invention is applied to a communication system that performs numerical control on a servo device has been described. However, the present invention is not limited to this and can be applied to any communication system.
In each of the above embodiments, the case where the branch line switch 16 and the trunk line switch 20 are mounted on the slave station has been described. However, the present invention is not limited to this, and the branch line switch 16 may be replaced with a trunk line, that is, a transmission line. The main line switch 20 may be provided between L2 and the connection unit 12 of the slave station, and between the master station M side of the branch line switch 16 and the connection unit 11 of the subsequent slave station.
[0044]
Further, in each of the above embodiments, the case where the master station M is connected to the end of the transmission line has been described. However, the present invention is not limited to this, and the case where the master station M is arranged in the middle of the transmission line is described. Can be applied. In this case, with respect to the slave station, the trunk switch 20 is provided at a position where a slave station located farther from the master station than the slave station can be separated from the trunk, and furthermore, at both ends of the transmission line. What is necessary is just to provide a termination resistor. By doing so, it is possible to connect the master station M and the slave station in the shortest way on the transmission line to which the slave station that performs data transmission is connected with reference to the master station M. In the transmission line on the other side with respect to the station M, the slave station is separated from the transmission line, so that noise can be reduced.
In each of the above embodiments, the branch line switch 16 corresponds to the branch line breaking means, and the trunk line switch 20 corresponds to the trunk line breaking means.
[0045]
【The invention's effect】
As described above, according to the communication system of claim 1 of the present invention, the branch line disconnecting means is provided on the branch line between the branch point to which the slave station is connected and the slave station, and the trunk line is further provided between the branch points. In the case where any of the slave stations performs data transmission, the slave station performing data transmission is set to a conductive state only with the branch line disconnection means that can be connected to the line, and the slave station performing data transmission is provided. Since the trunk line blocking means adjacent to the branch point to be connected and located on the far side from the master station is set to the open state, only the slave station performing data transmission is connected to the line, and Since the lines on the side farther from the master station of the slave station that performs data transmission are in a disconnected state, a portion corresponding to the disconnected cable or a branch line, and a slave station that does not perform data transmission. Effect of the impedance or the like due can be removed, it is possible to reduce noise.
[0046]
Further, according to the communication system of the present invention, the slave station is connected to the branch station cut-off means inserted into the branch line between the branch station to which the slave station is connected and the slave station. Main line cutoff means for disconnecting a slave station located farther from the master station from the line with respect to the branch point is provided, and the slave station conducts the branch line cutoff means when transmitting a response frame addressed to the master station. State and the trunk line disconnecting means open, connect the own slave station to the line, disconnect the line after the own slave station, and open the branch line disconnecting means when not transmitting data to the master station. In addition, the trunk line disconnecting means is made conductive, the own slave station is disconnected from the line, and the lines after the own slave station are set in a secured state. Means that only the slave station that transmits the response frame is connected, and the line after the slave station that transmits the response frame, which is farther from the master station, is cut off. The influence of impedance or the like by a considerable amount or branch line, or a slave station that does not perform data transmission can be eliminated, and noise can be reduced.
Furthermore, according to the communication system of the third aspect, since the master station is a terminal station, only cables required for communication between the master station and a slave station performing data transmission are provided. It can be effectively adjusted to be effective.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram showing an example of a communication system to which the present invention has been applied.
FIG. 2 is a timing chart for explaining the operation of the first embodiment;
FIG. 3 is an explanatory diagram for explaining an operation of the first embodiment;
FIG. 4 is an explanatory diagram for explaining the operation of the first embodiment;
FIG. 5 is an explanatory diagram for explaining the operation of the first embodiment;
FIG. 6 is a system configuration diagram illustrating an example of a communication system according to a second embodiment.
FIG. 7 is an example of a conventional half-duplex multi-drop communication system.
FIG. 8 is an example of a conventional full-duplex communication system.
FIG. 9 is an example of a conventional full-duplex serial multi-drop communication system using an external terminating resistor.
FIG. 10 is an example of a conventional full-duplex serial multi-drop communication system using an on-board terminating resistor.
[Explanation of symbols]
14 Receiver
16 branch line switch
18 Transceiver
20 Trunk switch
23, 27 Terminal switch
30 Switch switching circuit
100 communication system
R1, R2 terminator
R11, R12 Terminating resistor

Claims (3)

In a communication system in which a master station and a slave station are connected by a bus, and each station uses a line for transmitting data to the master station by the slave station at a timing that a plurality of stations do not use at the same time,
A branch line cut-off means inserted into a branch line between the slave station and the branch point of the line to which the slave station is connected, and for disconnecting the slave station from the line,
Main line cutoff means provided between each branch point of the line corresponding to each slave station, for separating a slave station located farther from the master station with respect to the slave station from the line. ,
When any one of the slave stations performs data transmission to the master station, among the branch line disconnecting means, only the branch line disconnecting means capable of connecting the slave station performing the data transmission to the line is made conductive, and A communication system, characterized in that a trunk line blocking means located adjacent to a branch point to which a slave station performing data transmission is connected and located farther from the master station is opened. A master station and a slave station are connected by a bus in full-duplex mode, a slave station receiving a transmission frame from the master station transmits a response frame to the master station, and the master station simultaneously transmits response frames from a plurality of slave stations. In a communication system adapted to transmit the transmission frame at a timing at which the transmission frame is not received,
The slave station is inserted in a branch line between the slave station and a branch point of the line to which the slave station is connected, and branch line cutoff means for disconnecting the slave station from the line.
Trunk cutoff means for disconnecting the slave station located farther from the master station from the line with reference to a branch point to which the slave station is connected,
The slave station, when transmitting a response frame addressed to the master station, the branch line cutoff means to the conductive state and the trunk line cutoff means to the open state,
A communication system, wherein when the data transmission to the master station is not performed, the branch line cutoff means is opened and the trunk line cutoff means is turned on. 3. The communication system according to claim 1, wherein the master station is a terminal station.

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