JPH04157839A - Line branching device - Google Patents

Abstract

PURPOSE:To select a line which is free from interference at the time of signal reception by delaying a received signal from one line through a delay circuit by a much longer time than a propagation time difference. CONSTITUTION:Signals when sent to lines A and B are received by line receivers 31A-R and 31B-R and the received signals are outputted, the received signals are outputted to AND gates 34 and 36 while the signal of the line A is sent directly and the signal of the line is passed through an 8-bit delay circuit; and they are inputted to carrier detecting circuits 38A and 38B. The delay time of the delay circuit 35 is so set that the delay of the line-A received signal behind the line-B signal due to the route difference between the two communication lines can be absorbed in case, so the detection signal from the line A is inputted earlier to a decision control part 7. If the line A is in this trouble, only the output of the line receiver 31B-R of the line B appears, so the received signal of the line B is sent out to a slave station line C.

Description

[Detailed Description of the Invention] [Summary] A signal reception method relating to a line branching device in a data transmission system that transmits and receives data between a master station and a plurality of slave stations connected in a multi-drop manner to a duplex communication line. The purpose of this device is to provide a line branching device that can select a line without interference, and is installed between the duplexed communication line and each slave station in order to connect multiple slave stations to the duplex communication line using a multi-drop method. A line branching device comprising: a carrier detection circuit connected directly to one communication line and via a delay circuit to the other communication line, and detecting the presence or absence of a received signal from the communication line; a determination control unit that determines the order in which the detection outputs from the detection circuit are generated and outputs a selection control signal on a first-come, first-served basis; and a determination control unit that selects one of the communication lines and connects it to the slave station based on the selection control signal. This configuration includes a switch section.

[Industrial application field]

The present invention relates to a line branching device in a data transmission system that transmits and receives data between a master station and a plurality of slave stations connected in a multi-drop manner to a duplex communication line.

[Conventional technology]

FIG. 3 is a block diagram of a conventional line duplexing system.

In building management systems, etc., the master station (building management device)
l has multiple slave stations (power equipment,
Each device (air conditioning equipment, water supply equipment, crime prevention/disaster prevention equipment, etc.) is connected to communication lines A and B, and the building's electricity usage, gas flow rate, water flow rate, voltage and current at various locations, elevator status,
Measured values and status information such as the condition of the security floor and whether or not a fire has occurred are constantly collected through polling, and automatically/as needed.
Buildings are managed by manually controlling these devices and displaying their status.

The plurality of slave stations 2 are connected to communication lines A and B from the master station in a multi-drop manner.

In such a transmission system, two communication lines A are connected via separate routes in order to duplicate the transmission line in case of an unexpected disaster.
, B may be provided.

In a transmission system that uses duplex communication lines, there are methods in which the sender selects one of the lines and sends a signal, and notifies the receiver of the selected line using another line, or the receiver sends a signal at an appropriate frequency. There is a method of detecting and selecting which line the signal is being sent to by switching the line. The former requires a third line to transmit the line selection signal, which increases the line cost, while the latter requires a switching cycle to monitor the presence or absence of a signal by switching the receiving line at a predetermined cycle. Difficult to set up. Therefore, a method can be considered in which the transmitting side always sends out transmission signals to both lines at the same time, and the receiving side receives the signals as one signal. This method includes, for example,
sends the same signal to the duplexed communication line via the hybrid circuit 9, and the multiple branch-connected slave stations 2 also receive the signal from each line via the hybrid circuit 9, and add the dual signal. is taken in as a received signal.

This hybrid circuit 9 is provided between a single-line station device and a duplexed communication line, and divides the transmission signal from the station device into two to create two communication lines A.

B, and the received signals from the two communication lines are combined and transmitted to the station equipment, and both communication lines A.

Prevent signal interference between 8.

[Problem to be solved by the invention]

However, in building management systems and the like, two communication lines are often installed on different routes for safety reasons. In this case, even if the transmitting device sends signals to both lines at the same time, the timing of the received signals will be different due to the difference in the route length of both lines from the transmitting position to the receiving position, so the same signal will be sent to both lines with a time difference. Since data is received from the line, there is a problem in that interference occurs and data cannot be received correctly. In particular, in the case of a multi-drop system, when a signal sent from a slave station to a dual line is received by another slave station, interference due to the double line often occurs, resulting in reception errors (such as hybrid There was a problem in that connection by circuit was practically impossible.

The present invention was created in view of the above problems, and an object of the present invention is to provide a line branching device that can select a line without interference when receiving a signal in a multi-drop information transmission system using duplex lines.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle configuration of a line branching device according to the present invention.

The above problem arises as shown in Figure 1, in order to connect a plurality of slave stations 2 to the duplex communication lines A and B using a multi-drop method, there is a gap between the duplex lines A and B and each slave station 2. A carrier detection device is provided in the line branching device 3, which is connected directly to one communication line A and connected to the other line via a delay circuit 35, and detects the presence or absence of received signals from communication lines A and B. circuits 38A and 38B, a determination control unit 7 that determines the order in which detection outputs from the carrier detection circuits 38A and 38B are generated and outputs selection control signals on a first-come, first-served basis; This problem is solved by the line branching device of the present invention, which is characterized by having a switch section 8 that selects one of the terminals and connects it to the slave station.

[Effect]

Signals sent simultaneously from the master station and other slave stations to the duplex communication line arrive at the branch circuit on the receiving side with a transmission time difference due to line length, but it is uncertain which line the signal comes from first. be. However, within the line branching device, the received signal from one line (for example, 8 lines) is delayed by a delay circuit that is sufficiently long compared to the above-mentioned propagation time difference, and then input to the carrier detection circuit. Therefore, when both lines are normal, the delayed carrier detection signal from the low-priority line is always generated after the high-priority line. Since you select to connect to the station, subsequent signal reception will be done via this line. Further, when the priority line is in failure, the reception signal from the priority line is not detected, and the reception signal is received only from the low priority line via the delay circuit. Therefore, since only the received signal from one line is transmitted from the branching device to the slave station device, the received signal is correctly received without causing any interference on the receiving side.

〔Example〕

The present invention will be explained in detail below with reference to the accompanying drawings.

FIG. 2 is a circuit diagram of an embodiment of the present invention. Note that the same reference numerals represent the same objects throughout the plan.

In the figure, A and B are dual, balanced communication lines,
This is a communication line for transmitting and receiving data with the master station.

Each of the plurality of slave stations 2 is branch-connected to this line by a slave station line C via a line branching device 3, and data and commands are exchanged by half-duplex communication between the master station and the slave stations. Sending and receiving takes place.

Data transmission using these communication lines is based on 9600b based on the specified line interface standard for the transmission line.
This is done by transmitting and receiving digital signals of IT/sec.

In the figure, the line branching device 3 includes line interface sections 31A, 31B, and 31C, and a carrier detection circuit 38A.

38B, 38C, delay circuit 35, judgment control circuit 7, AN
(D game) 81, 82 and an OR gate 83. Line interface section 31A
.

31B and 31C are provided corresponding to the duplex communication lines A and B and the slave station line C, and constitute a line interface based on the R8-485 standard capable of l:n multipoint long distance transmission. Each interface section 31
A, 31B, and 31C are composed of a line driver D that sends signals to the line, and a line receiver R that receives signals from the line. Line receiver 31C- on slave station line side
The output of H is branched into two and input to two line drivers 31A-D and 31B-D on the communication line side. The outputs of the input line line receivers 31A-H are directly AND gated) 81
The outputs of the eight line receivers 31B-H are input to the delay circuit 3 which provides a predetermined delay time (e.g. 8 bits).
5 and input to AND gate 82. The outputs of the two AND gates 8L and 82 are input to the line dryer/<3IC-D of the slave station line C via an OR gate 83. All line receivers 31A-R, 31B-R, 31C-H
The outputs of the corresponding carrier detection circuits 38A and 38B
, 38C, and output a carrier detection signal when a received signal from the line is detected. These carrier detection signals are input to the determination control circuit 7. This determination control circuit 7 is composed of a gate and a priority encoder, and detects which of the three carrier detection signals arrives first, and outputs a 3-bit selection control signal. Two AND gates and two line drivers are controlled by this selection control signal. First, when the slave station l transmits to respond to a polling request from the master station, the line receiver 31C-R receives the transmission signal from the slave station line C, and the carrier detection circuit 38C detects the carrier. Since the signal is output, the determination control unit 7 outputs a selection control signal in which bit 1 is "H" and bits 2 and 3 are "L". As a result, the line drivers 31A-D and 31B-D on the line side are enabled, convert the received signal from the slave station device into a predetermined form, and send it to both communication lines A and B, as well as the two AND games) 33 .36 to block incoming signals from communication line AB. That is,
Even if the transmission signal from the own station reaches the line receivers 31A-R and 31B-H on the line side during this period, it is blocked by the respective AND gates and is blocked by the line receiver 31 of the slave station line.
It is not input to 1C-D.

Next, a signal is transmitted to line A/B without any transmission from the own station (then, line receivers 31A-R, 31
The received signals are output directly to the 6 lines and through an 8-bit delay circuit to the AND gate (34 and 36), respectively, and are input to the carrier detection circuits 38A and 38B.

The delay time of the delay circuit 35 is set so that it can absorb even if the received signal on the line A side is delayed from the line B side due to the route difference between the duplex communication lines. The detection signal is input first, and the determination control unit 7 determines that the second bit is "H" and the 1.3rd bit is "L".
outputs a selection control signal. As a result, the AND gate 81 is turned ON, the AND gate 82 is turned OFF, and the line A
The outputs of the line receivers 31A-H are input to the child station line side driver 310-D, and the communication line side drivers 31A-D and 31B-D are disabled. Therefore, only the received signal on the line A side is sent to the slave station line C, the received signal on the line B side is prevented from being sent to the slave station line C, and signal interference between lines A and B is prevented. be done.

When line A is out of order, line cash register on line A side /<31
There is no output on A-H, and the line receiver 31B on the line B side
Since only the -H output appears, only the third bit of the output from the determination control section 7 becomes "H". As a result, the AND gate 82 is turned on, and the received signal on line B is connected to slave station line C.
At the same time, the line driver 31 on the communication line side
A-D, 31B-D are disabled and line B
This prevents the received signal from leaking to line A.

As described above, by delaying the received signal on one line and allowing the received signal on the other line to arrive first, a high priority is given to the other line, and that line is connected to the slave station line, and a low priority line is connected. Therefore, even if a signal is sent to both duplicated lines, it will normally capture six lines,
Interference of received signals does not occur at the receiving terminal station, and normal receiving operations can be performed.

〔Effect of the invention〕

As explained above (according to the branch circuit of the present invention, the slave station device receives the signal from the line given high priority, so even if the same signal is always sent to the duplicated communication line, the multi-drop method is not possible). The connected slave station devices always receive one signal, ensuring good communication without interference.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of a line branching device of the present invention, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a block diagram of a line duplexing system according to the prior art. In the figure, l... Master station, 2... Slave station, 3... Line branching device, 31A, 31B, 31C... Line interface section, 35... Delay circuit, 38A, 3
8B, 38C...carrier detection circuit, 7-judgment control unit (circuit), 8-switch unit, A, B...duplex communication line, C...slave station line.

Claims (1)

[Claims] In order to connect the duplex communication line (A, B) and a plurality of slave stations (2) in a multi-drop manner, the duplex communication line (A, B) is
A, B) and each slave station (2) is a line branching device (3) installed between the communication line (A) directly and the other communication line (A).
B) includes carrier detection circuits (38A, 38B) that are connected to each other via a delay circuit (35) and detect the presence or absence of a received signal from the communication lines (A, B), and the carrier detection circuits (38A, 38B). a determination control unit (7) that determines the order in which the detection outputs are generated and outputs a selection control signal on a first-come, first-served basis; switch section (8) that connects to the slave station (2)
A line branching device comprising: