JPH0583018B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a communication system having one primary station and a plurality of secondary stations.

[Conventional technology]

One of the formats for connecting one primary station and a plurality of secondary stations to a transmission line is a multi-drop format as shown in FIG. In the illustrated multi-drop communication system, one primary station 1' and one primary station 4
It has three secondary stations 2 _-1 , 2 _-2 , 2 _-3 and 2 _-4 ,
The transmitting/receiving circuit 11 of the primary station 1' is connected to one end of the transmission line 3, and the transmitting/receiving circuits 21 of the secondary stations _2-1 , _2-2 , _2-3 , and _2-4 are branch-connected to the transmission line 3. There is. Furthermore, in the illustrated example, the transmission line 3 consists of two transmission lines 31 and 32 in order to perform transmission and reception separately. That is, the transmitter T _x of the transmitter/receiver circuit 11 of the primary station 1' is connected to one end of the transmission line 31, and the transmitter/receiver of the secondary stations 2 _-1 , 2 _-2 , 2 _-3 and 2 _-4 is connected to one end of the transmission line 31 . The receiving section R _x of the circuit 21 is branch-connected, and the receiving section R _x of the transmitting/receiving circuit 11 of the primary station 1' is connected to one end of the transmission line 32, and the secondary stations 2 _-1 , 2 _- are connected to the transmission line 32 . The transmitting sections _Tx of each transmitting/receiving circuit 21 ₂ , _2-3 , and _2-4 are branch-connected.

As a transmission control procedure of this communication system, for example, a high-level data link control procedure (hereinafter abbreviated as HDLC procedure) is used. Second
The figure shows an example of the frame structure of the HDLC procedure. In the figure, F is a flag sequence, A is an address field, C is a control field, I is an information field, and FCS is a frame check sequence.

The contents contained in the control field C in the frame of the primary station and each secondary station are command information and response information, respectively, and the primary station sends a command, and the secondary station receives the command and returns a response. . The data link is established by transmitting a normal response mode setting command from the primary station to the secondary station designated by address field A in the frame.

Referring to FIG. 8, one transmission line (pair of lines) 3 includes one primary station 1' and four secondary stations 2 _-1 ,
An example of a communication system in which _2-2 , _2-3 and _2-4 are connected in a multi-drop format is shown. In this example, since data is transmitted and received through one transmission path, the transmitting and receiving circuit 11 of the primary station 1' and the secondary station 2 _-1 ,
Each transmitting/receiving circuit 21 of _2-2 , _2-3 , and _2-4 has a fourth
Three windings (primary winding n ₁ ,
It includes pulse transformers 111 and 211 having a secondary winding n ₂ and a tertiary winding n ₃ ).

The primary station 1' is, as shown by the solid line in FIG.
Transmission data is sent as a positive pulse to the transmission line 3 via the primary winding n ₁ and secondary winding n ₂ of the pulse transformer 111, and the negative pulse on the transmission line 3 is sent to the secondary winding n ₂ , received through the tertiary winding n ₃ . on the other hand,
As shown by the dotted line in FIG.
Transmission line 3 via primary winding n ₁ and secondary winding n ₂ of 11
The pulse of positive polarity on the transmission line 3 is received via the secondary winding n ₂ and the tertiary winding n ₃ .

A basic mode control procedure is used as a transmission control procedure for this communication system, and a polling/selecting method is adopted to establish a data link. That is, only when a primary station designates a certain secondary station and invites it to send (or receive) data, that secondary station starts a sending (or receiving) operation.

Alternatively, in both the examples shown in FIGS. 7 and 8, data transmission and reception may be performed in a time-division manner. For example, in the case of FIG. 7, the primary station 1' sends data to each secondary station _2-1 to _2-4 in a time-division manner via the transmission line 31, and each secondary station _2-1 to _2-4 Synchronization is established based on the signal sent from the primary station 1', and by reproducing the timing signal, data is sent to the primary station 1' via the transmission line 32 for the time allotted to the local station. In addition, in the case of Fig. 8, the primary station 1'
The secondary stations 2 _-1 to 2 _-4 transmit and receive data at predetermined intervals, and only one secondary station can transmit data to the primary station 1' at a given time. Note that in any of these time division systems, the secondary station cannot send data to the primary station unless it receives data from the primary station.

[Problem that the invention seeks to solve]

In such a configuration, for example, secondary station 2 _-1
A certain point on the transmission line 3 between 2 _{and 2} (point in Figure 7)
If x ₁ or x ₂ (point x ₃ in Figure 8) is disconnected,
Data communication between the secondary stations 2 _-2 , 2 _-3 and 2 _-4 and the primary station 1' becomes impossible. The only way to recover from this is to repair the cut point, which has the disadvantage that the system will be down for a long time.

[Means for solving problems]

A communication system according to the present invention has one primary station and a plurality of secondary stations, the primary station has a first transmitting/receiving circuit connected to one end of a transmission path, and each secondary station is connected to one end of a transmission path. In a multi-drop type communication system having branch-connected transmitting and receiving circuits, the primary station selects either the second transmitting and receiving circuit connected to the other end of the transmission path, or the first or second transmitting and receiving circuit. and a control circuit for operating the device.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, the communication system of this embodiment includes one primary station 1 and four secondary stations 2 _-1 , 2 _-2 ,
_2-3 and _2-4 . The primary station 1 includes a first transmitting/receiving circuit 11 connected to one end of the transmission line 3;
A second transmitting/receiving circuit 1 connected to the other end of the transmission line 3
2, a selection switch 13 for selecting either the first transmission/reception circuit 11 or the second transmission/reception circuit 12, and a control circuit 14 for controlling the selection switch 13. The transmitter/receiver circuit is not just a signal level converter, but also has the function of converting a parallel signal input from the control circuit 14 into a serial signal and transmitting it, and converting a serially received signal into a parallel signal and passing it to the control circuit. have. The secondary stations 2 _-1 , 2 _-2 , 2 _-3 and 2 _-4 each have a transmitting/receiving circuit 21 branch-connected to the transmission path 3 .

In this embodiment as well, the transmission line 3 consists of two transmission lines 31 and 32, as in FIG. The transmitter T _x of the first transmitter/receiver circuit 11 of the primary station 1 is connected to one end of the transmission path 31 , and the transmitter T _x of the second transmitter/receiver circuit 12 is connected to one end of the transmission path 31 .
is connected to the other end of the transmission line 31, and the secondary stations 2 _-1 , 2
_-2 , _2-3 and _2-4 receiving section R _x of each transmitting/receiving circuit 21
is branch-connected to the transmission line 31. On the other hand, the receiving section R _x of the first transmitting/receiving circuit 11 of the primary station 1 is connected to one end of the transmission path 32 , and the receiving section R
_{The receiving} section _{R x of}
One transmitter T _x is branch-connected to the transmission line 32 .

The transmission control procedure of this embodiment is an HDLC procedure with a frame structure as shown in FIG.

Next, the operation shown in FIG. 1 will be explained.

Normally, the control circuit 14 of the primary station 1 controls the selection switch 13 to select the first transmitting/receiving circuit 11 side as shown in the figure. Therefore, the data (command) sent from the control circuit 14 of the primary station 1
is sent to the transmission path 31 from the transmitter T _x of the first transmitter/receiver circuit 11 . In each secondary station 2, when a control circuit (not shown) receives the command via the receiving section _Rx of the transmitting/receiving circuit 21, the transmitting section _Tx of the transmitting/receiving circuit 21 sends a response to the transmission path 32.
The control circuit 14 of the primary station 1 receives the response on the transmission path 32 via the receiving section R _x of the first transmitting/receiving circuit 11 .

In this state, if point x ₁ of transmission line 31 or point x ₂ of transmission line 32 between secondary stations 2 _-1 and 2 _-2 is disconnected, primary station 1 connects secondary stations 2 _-2 , 2 _- No response received from ₃ and _2-4 . Therefore,
The control circuit 14 of the primary station 1 controls the selection switch 13 to select the second transmitting/receiving circuit 12 side so that transmission and reception can be performed with the secondary stations 2 _-2 , 2 _-3 and 2 _-4 . . As a result, the control circuit 1 of the primary station 1
4 receives the responses from the secondary stations 2 _-2 , 2 _-3 and 2 _-4 on the transmission line 32 to a receiving section of the second transmitting/receiving circuit 12.
Can be received via _Rx .

Note that in the case of a failure in the secondary station itself, there is no response to commands from both the first transmitting/receiving circuit 11 and the second transmitting/receiving circuit 12, so the control circuit 14 of the primary station 1: Since a disconnection has occurred, it can be determined whether a failure has occurred in the secondary station itself.

Also, in the above explanation, normally, the primary station 1
Transmission/reception is performed with the secondary station using only the transmitting/receiving circuit 11 side, and when a response is not received from the secondary station, the first transmitting/receiving circuit 11 is switched to the second transmitting/receiving circuit 12. , the first transmitting/receiving circuit 11 and the second transmitting/receiving circuit 12 may be switched and used at all times. In this case, if a secondary station does not respond to a command even when both transmitting/receiving circuits 11 and 12 are used, it is determined that the secondary station itself has failed, and if only one transmitting/receiving circuit responds, the It is possible to determine that the line is disconnected, and to determine the location of the disconnection (on which transmission line between secondary stations the disconnection is occurring) based on the response pattern.

In the above embodiment, the primary station has two transmitting/receiving circuits, but it may have three or more transmitting/receiving circuits. For example, in FIG. 1, the primary station 1 further has a third transmitting/receiving circuit branch-connected to the transmission line 3 of the secondary stations _2-2 and _2-3 , and the first, second, or third transmitting/receiving circuit One of the circuits is selected by the selection switch 13 by the control circuit 14. With this configuration, for example, even if a disconnection occurs not only on the transmission path between secondary stations _2-1 and _2-2 , but also on the transmission path between secondary stations _2-3 and _2-4 , , the primary station 1 can communicate with all secondary stations.

Also in the embodiment shown in FIG. 1, data transmission and reception may be performed in a time-division manner as described above.

Referring to FIG. 3, the configuration of another embodiment of the communication system according to the present invention is shown, in which one primary station 1 and one primary station 4 are connected to one transmission path 3, similar to FIG.
Two secondary stations 2 _-1 to 2 _-4 are connected. In this embodiment _, as _in FIG. 8 _, as shown in _FIG. Transmission/reception circuit 21
includes a pulse transformer with three windings. Further, the basic mode control procedure is used as the transmission control procedure of this embodiment, and the polling/selecting method is adopted for establishing the data link.

In this embodiment as well, as in the embodiment shown in FIG.
For example, secondary stations 2 _-1 and 2 _-2
Even if point x ₃ of the transmission path 3 between them is disconnected, the primary station 1 can communicate with all secondary stations. Furthermore, data transmission and reception may be performed in a time-division manner as described above.

Referring to FIG. 5, the configuration of still another embodiment of the communication system according to the present invention is shown, in which an optical fiber is used as the transmission line 3. Primary station 1
The secondary stations 2 _-1 , 2 _-2 , 2 _-3 , and 2 _-4 are connected to the transmission path 3 via nodes 40, 41, 42, 43, and 44, respectively. Primary station 1 and secondary station 2
The internal configurations of _-1 , _2-2 , _2-3 , and _2-4 are the same as those in FIG. The nodes 40 to 44 consist of an optical-to-electric conversion circuit O/E, an electric-to-optical conversion circuit E/O, and an OR circuit.

The operation of this embodiment is substantially the same as that of FIG. However, in this embodiment, a node may fail. For example, suppose that the node 42 fails while the control circuit 14 in the primary station 1 selects the first transmitting/receiving circuit 11 side with the selection switch 11. At that time, primary station 1 is secondary station 2 _-1
Communication is possible only between The control circuit of the primary station 1 selects the second transmitting/receiving circuit 1 using the selection switch 11.
When controlling to select side 2 and sending a command, responses are returned from secondary stations _2-3 and _2-4 . Therefore, the control circuit 14 can determine that the node 42 has failed.

In this embodiment, the primary station has two transmitting/receiving circuits, but it may have three or more transmitting/receiving circuits. FIG. 6 shows an example in which the primary station 1 further includes a third transmitting/receiving circuit 15. However, since the transmission line 3 is an optical fiber, the node 40
is different from that in Figure 5.

FIG. 9 shows another embodiment of the present invention, in which the primary station 1 in another embodiment is shown separately. The primary station 1 has three central processing units CPU1,
It has a CPU 2 and an HCPU, and the CPU 1 and CPU 2 can control the husband's transmitting/receiving circuits T _x and R _x and can independently perform predetermined communication procedures. CPU
1. The CPU 2 and the HCPU are connected by a bus line, and data can be transferred in any direction between the three, and such a bus line system is commonly used.

CPU1 and CPU2 are configured to mutually exclusively perform transmission and reception processing. That is, CPU1 polls the secondary station, checks the response from the secondary station, and
Furthermore, if there is no data to be sent to the secondary station, CPU2
Exclusive control is performed to pass the right to perform transmission and reception processing to. With this kind of configuration,
The HCPU can transfer data to the secondary station without timing any switching to CPU1 or CPU2.

In addition, in this embodiment, CPU1, CPU2 and
Although we have shown a hardware method in which HCPUs are connected by bus lines, it is also possible to consider these as three programming processing units and to connect these processing units using programming data transfer means and exclusive control means. It is possible,
It is clear that this does not depart from the scope of the invention.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, the transmission line is cut off while the primary station is transmitting and receiving data using one of the transmitting/receiving circuits, and communication with the primary station becomes impossible. Even if there is a next game,
By transmitting and receiving data at the primary station using the other transmitting/receiving circuit, there is an effect that it is possible to communicate with the secondary station that has become unable to communicate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the communication system according to the present invention, FIG. 2 is a diagram showing an example of the frame structure of the HDLC procedure used in the communication system of FIG. 1, and FIG. 4 is a block diagram showing the configuration of another embodiment of the communication system according to the present invention, FIG. 4 is a diagram showing an example of a pulse transformer included in the transmitting/receiving circuit of FIG. 3, and FIG. A block diagram showing the configuration of yet another embodiment of the system, FIG. 6 is a block diagram showing a modification of FIG. 5, and FIG. 7 is a block diagram showing an example of a conventional multi-drop type communication system. , FIG. 8 is a block diagram showing another example of a conventional multi-drop type communication system, and FIG. 9 is a block diagram of a primary station showing another embodiment of the present invention. 1...Primary station, _2-1 to _2-4 ...Secondary station, 11,
12... Transmission/reception circuit, 13... Selection switch, 1
4...control circuit, 21...transmission/reception circuit, 3...transmission line.

Claims (1)

[Claims] 1 The only primary station connected to one transmission line,
In a communication system having a plurality of secondary stations sequentially connected in a multi-drop format from one end of the transmission path to the other end, the primary station includes a first transmitting/receiving circuit connected to one end of the transmission path; a second transmitting/receiving circuit connected to the other end of the transmission path; a switching circuit that exclusively switches between the first and second transmitting/receiving circuits; and a switching circuit that controls the switching circuit and switches between the first transmitting and receiving circuit or the second a communication control circuit that selects a transmitter/receiver circuit to communicate with the secondary station, and performs communication from both directions of the transmission path.