JPS5947505B2 - data transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data transmission device in which a plurality of terminal devices are connected to one central device via a common transmission path, and in particular, the present invention relates to a data transmission device in which a plurality of terminal devices are connected to one central device via a common transmission path, and in particular to The present invention relates to a data transmission device that processes transmission requests from.

Recently, in order to centrally control multiple terminal devices that are dispersed over a distance, data transmission devices in which these terminal devices are connected to one central device via a common transmission path have become widely used. I came.

In such a data transmission device, there is a problem of how to process simultaneously occurring transmission requests, and various solutions have been proposed in the past. In order to solve the above-mentioned problems, conventional data transmission devices use a center polling method or an end call method.

In the center polling method, the central processing unit polls each terminal device sequentially, for example, in the order in which the common transmission path is connected, to see if there is a transmission request, and then transmits to the terminal device for which a transmission request is detected first. It is a method of forgiveness.

A disadvantage of the center polling method is that when there are a large number of terminal devices, the time from when a transmission request is generated until the transmission request is detected by the central device and allowed to be transmitted, that is, the waiting time, generally becomes long. . On the other hand, the disadvantage of the end call method is that it does not require long waiting times like the center polling method. In this case, accurate data transmission may not be possible.

The present invention has been made in order to solve the above-mentioned drawbacks, and the present invention has been made to solve the above-mentioned drawbacks. An object of the present invention is to provide a data transmission device that allows only terminal devices to transmit data.

The data transmission device &ζ of the present invention is formed by connecting a plurality of terminal devices to one solid device via a common transmission path.

The common transmission line is a 4-wire line, each consisting of a 2-wire transmission line and a 2-wire reception line. A carrier signal sent out from one terminal device for transmission is transmitted via the transmission line to the solid device, amplified by the solid device, and sent out again to the receiving line, thereby transmitting it to the other terminal device. The transmitter is configured to prevent the transmission of a new carrier signal that would cause interference. On the other hand, after detecting the end of transmission to a terminal device that has entered a waiting state due to transmission from another terminal device due to the discontinuation of the carrier signal, the carrier signal continues to be transmitted until the time corresponding to the priority given to that terminal device. The device is configured so that when no signal is detected, the device enters a transmission state and is allowed to send out a carrier signal. In other words, terminals with a higher priority are allowed to transmit carrier signals in a shorter waiting time after detection of discontinuation of the carrier signal, and as a result, the priority order for simultaneous transmission requests that occur between multiple terminal devices is lowered. Control is exercised. The solid device further prevents all terminal devices from transmitting, so
A carrier signal is also sent to the receiving line at times other than when the data ring is being established. The data transmission device of the present invention will be explained in detail below with reference to the drawings, but the common transmission line only needs to be at least one 4-wire common transmission line, and is mainly a transmission line attached to a railway line or a public transmission line. A dedicated line can be used as this common transmission line, and the data transmission device of the present invention is realized.

FIG. 1 is a block diagram showing one embodiment of a data transmission device according to the present invention. In FIG. 1, a solid device 1 has a transmission control circuit (not shown) connected via a modulator 1a and a demodulator 1b, and transmits and detects a carrier signal and also controls data transmission devices such as polling. It has various normal transmission and reception control functions necessary for configuration. The modulator 1a is connected to the amplifier 1d via the normally open contact NO of the switch 1c, which in turn is connected to the receiver path 2. A demodulator 1b is connected to a transmission line 3 attached to the reception line 2 via an amplifier 1e and a resistor 1f. In addition, the transmission line 3 is an amplifier 1e11g1 switch 1
It is connected to the reception line 2 via the normally closed contact NC of c and the amplifier 1d. In other words, since the amplifiers 1d and 1e function as relay amplifiers, the data transmission device 1 also forms a return transmission path using the reception line 2 and the transmission transmission line 3. The terminal devices 4 to n all have the same configuration and are connected to the solid device 1 using the receiving line 2 and the transmitting line 3 as a common transmission path.

To explain in detail using the terminal device 4 as an example, the terminal device 4 connects a demodulator 4a to the receiving line 2 in a branch-connected manner, and then the demodulator 4a is connected to a transmission control circuit 4b. The transmission control circuit 4b has normal functions regarding transmission and reception. On the other hand, the terminal device 4 is connected to the transmission line 3 via a modulator 4c and a switch 4d, and the switch 4d is closed during transmission by the transmission control circuit 4b. The data transmission apparatus of the present invention configured as described above performs the following operations in establishing a data link for transmission and releasing the data link.

In establishing a data link, first, only the terminal device 4 issues a transmission request, and other terminal devices 5 to n including the solid device 1
The case where there is no transmission request and is in a standby state will be explained. Since no carrier signal is detected on the transmission control circuit 4b1ζ reception line 2 of the terminal device 4, the switch 4d is closed and the carrier signal is sent to the transmission line 3 via the modulator 4c. In this case, the carrier signal is, for example, an intermittent signal capable of transmitting a digital code, and the solid device 1 uses the received carrier signal to determine which of the terminal devices 4 to n is in the transmitting state. can be identified. That is, the carrier signal is transmitted through the transmission line 3, the resistor 1f, and the demodulator 1b.
The signal is guided to the transmission control circuit via the terminal device 4, and it is determined which of the terminal devices 4 to n is transmitting the signal. At the same time, the carrier signal is transmitted from the transmission line 3 to the reception line 2 via the amplifier 1e1, the resistor 1g, the switch 1c, and the amplifier 1d.
It is also transmitted to Therefore, each terminal device 5 to n is connected to the receiving line 2.
Since a carrier signal is detected at this point, even if a transmission request occurs after this point, the transmission state cannot be entered until the carrier signal is no longer detected.

When the transmission control circuit of the solid device 1 detects the presence of a carrier signal on the transmission line 3, it switches the switch 1c to connect the modulator 1a to the amplifier 1d, and then closes the switch 4d from the transmission control circuit to the terminal device 4. Sending out instructions to continue to accomplish
A data link is established here. Central device 1
Following the establishment of the data link, the other terminal devices 5 to 5
In order to prevent the transmission of a new carrier signal causing interference from n, a carrier signal is transmitted from the solid device 1 to the receiving line 2, and the carrier signal continues to be transmitted until the data link is released. 1. When releasing the data link, the solid device 1 sends a command to the transmission line 2, and the terminal device 4 detects this command and opens the switch 4d.

Furthermore, the solid device 1 switches the switch 1e to the resistor Ig side to stop sending out the carrier signal, and here the data ring is switched.
, a release is made. Terminal device n during data ring establishment
The case where a transmission request occurs at -l and n will be explained.

As mentioned above, since the carrier signal is being sent from the solid device 1 while the data link is being established, even if the transmission request 2 occurs, the terminal device n-1 or n cannot immediately enter the transmission state. Therefore, terminal devices n-1 and n are placed in a waiting state until no carrier signal is detected.
FIG. 2 is a waveform diagram showing timing for explaining priority control among the terminal devices 4 to n shown in FIG.

In the data transmission device of the present invention, the priority among the terminal devices 4 to n is determined according to the order of connection from the solid device 1, and the priority is determined so that the terminal device 4 has the highest priority. In other words, the higher the priority of the terminal device, the shorter the time it takes to transmit the carrier signal after the carrier signal is interrupted. Time 1, as shown in Figure 2a.

At this point, the data link of the terminal device 4 (FIG. 2c) is released, and the carrier signal on the receiving line 2 is cut off.

This causes the terminal device n-1 to have the power to send a carrier signal to the transmission line 3 at the time tl (d in FIG. 2, and the terminal device n at time T3 (e in FIG. 2). In this case, the terminal device Since n-1 starts transmitting the carrier signal at time tl, terminal device n detects the presence of the carrier signal again at time T2 (Fig. 2b), and eventually terminal device n starts transmitting from time T3. The transmission of the carrier signal to line 3 is prevented. In this case, the difference between time tl and T3 may be sufficient to establish the priority order between terminal device n and terminal device n-1; Includes the time from when terminal device n starts sending a carrier signal to transmission line 3 until it is turned back by solid device 1 and sent to reception line 2, and then demodulated and detected by each terminal device 4 to n. If any of the terminal devices 4 to n accidentally enters the transmitting state at the same time due to some reason, such as noise, then ι
Naturally, the solid device 1 cannot receive data correctly due to interference.

In this case, the solid device 1 performs polling again from the solid device 1 without establishing a data link with any of the terminal devices 4 to n, and sends data to any one of the terminal devices 4 to n according to the priority order. Resolved by establishing a link. FIG. 3 shows another embodiment of the data transmission device according to the invention.

Receiving lines 2a) 2b and 2c are connected to the amplifier 1d of the solid device 1 via resistors 1h1i and 1j, respectively, and transmitting lines 3a) 3b and 2c are connected to the amplifier 1e via resistors Ik) 11 and 1m, respectively. 3c are connected to each other. A terminal device 4e is connected to the reception line 2a and the transmission line 3a.
-Ne are connected to each other, and similarly the receiving line 2b
Terminal devices 4f to Nf are connected to the transmission line 3c, and terminal devices 4g to Ng are connected to the reception line 2c and the transmission line 3c, respectively. The operation of the data transmission device in this case is almost the same as that described in FIG. In any case, one of the terminal devices 4e-Ne) 4f-Nf) 4g-Ng will be in the transmitting state, and the receiving lines 2a, 2b and 2
A carrier signal is sent from the solid device 1 via c, and duplicate transmissions are prevented. Note that the common transmission path may be constructed by frequency division so that the reception line 2 and the transmission line distance 3 are two-wire lines.

Furthermore, it is clear that the priority order among the terminal devices 4 to n does not need to be limited to the order of connection. As explained above, according to the present invention, the terminal equipment is allowed to transmit when no carrier signal is detected on the receiving line for the time determined by the priority order, and this allows simultaneous transmission requests. This has advantages such as being able to control transmission without causing interference even if interference occurs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the data transmission device according to the present invention, FIG. 2 is a waveform diagram showing timing for explaining the operation of FIG. 1, and FIG. 3 is a block diagram showing another embodiment of the data transmission device according to the present invention. FIG. 2 is a block diagram showing an example. ...Solid device, 1a14d, . nd...Modulators 4a, . na... Demodulator, 1c14d, . nd
Switch, 1d11e...Amplifier, 2...
- Receiver 3...Transmission lines 64-n...Terminal device.

Claims (1)

[Claims] 1. In a data transmission device in which a plurality of terminal devices are connected to one central device via a common transmission path, a common transmission path including a unidirectional four-wire reception line and a transmission line; The central device relays and amplifies the carrier signal received via the transmission line and sends it out to the reception line, and then transmits the carrier signal during establishment of a data link, and the central device detects a carrier signal on the reception line for a certain period of time. and the terminal device that sends out a carrier signal for transmission when the terminal device is not used. 2. The data transmission device according to claim 1, wherein the fixed time during which no carrier signal is detected on the reception line is set to be shorter for terminal devices with higher priority. 3. The data transmission device according to claim 1, wherein the common transmission path is a common transmission path composed of a plurality of reception lines and transmission lines branched and connected in a central device. . 4. The data transmission device according to claim 1, wherein the common transmission path is a two-wire common transmission path composed of a frequency-divided reception line and a transmission line.