JPS6382138A - Slave station leadership type data communication line system - Google Patents

Abstract

PURPOSE:To contrive the improvement of the line utilizing efficiency by providing a carrier detection means detecting whether or not a private main line is used by other slave station to each slave station. CONSTITUTION:A CPU 6 built in a slave station 2 is connected to a branch line 4 and a carrier detection circuit 7 is provided between a private main line 3 and the CPU 6 as a bypass circuit. The carrier detection circuit 7 is so interconnected that it detects a voltage between the line 3 and the CPU 6 when a communication trigger is applied to the slave station 2 and discriminates whether or not the private main line 3 is already in use depending on the voltage. That is, in appling communication trigger from the slave station 2 to a master station 1, the carrier detection circuit 7 detects whether the private main line 3 is used by other slave station or not. In case of the discrimination of not in use, the line is connected between the slave station 2 and the master station 1 and the communication enable state is attained. Thus, it is not required to introduce the polling/selecting system between the master station 1 and the slave stations 2, 2 and smooth communication is attained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a slave-initiated data communication line system in which a slave station receiving data can request data transmission from a master station transmitting data. It is related to.

[Prior Art] Actual typical examples of configuring data links between computers or between computers and terminal devices in a data communication line system are shown in FIG. 3 or 4.
The system shown in the figure is already known. Figure 3 shows a so-called direct line system in which a master station A that sends data and a slave station that receives data are directly connected by a dedicated line C. It has been adopted. Further, in Fig. 4, a master station a and a plurality of slave stations b... This is a so-called branch line system in which the network and the network are interconnected. This branch line method is generally adopted when the distance to be transmitted is long and the amount of data is small, and because it has a higher concentration density than the direct line method mentioned above, the transmission cost is lower. The line is economical.

[Problems to be solved by the invention] However, the above-mentioned branch line type data communication line system has conventionally been main station-driven, and data transmission and reception has been based on the so-called polling/selecting method. . As is well known, this polling/selecting method consists of a master station a, each slave station, b...
..., in turn asking if there is a transmission request (this is called polling), and if there is a slave station waiting for transmission data, it transmits the data. Also, when master station A wants to send data to slave station A, it asks "I have data to send, but can it be received?" (this is called selecting).
The message is sent after waiting for a response that it can be received. Therefore, according to this polling/selecting master station-driven data communication line system, it is not possible for the slave station to directly issue a communication trigger to the master station to request data transmission. In this case, since the dedicated line is connected only after polling from the main station, there is inevitably a waiting time (access time).
was long, and the usage efficiency was poor.

[Object of the Invention] The present invention has been devised in view of such conventional problems, and its purpose is to provide a slave-initiated system in which a communication trigger can be applied from the slave side to the master station. Our goal is to provide a data communication line system for This aims to shorten the access time on the slave side and improve line usage efficiency.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a system in which a main station that transmits data and a plurality of slave stations that receive data are connected to a dedicated trunk line and a plurality of branch lines branching from the main station. A slave station-driven data communication line system in which at least each slave station is provided with carrier detection means for detecting whether or not the dedicated trunk line is being used by another slave station, in a data communication line interconnected by two slave stations. The main points are as follows.

"Operation" When the slave station issues a communication trigger to the master station, the carrier detection means determines whether the dedicated trunk line is being used by another slave station.If it is not in use, the slave station A line is established between the main station and the main station, and subsequent communication becomes possible.

[Example] An example of the present invention will be described below with reference to FIGS. 1 and 2. In the illustrated data communication line, a master station 1 that transmits data, such as a computer, and slave stations 2, 2, etc. that receive data are connected to one dedicated trunk line 3 and multiple lines branching from it. are mutually connected by branch lines 4, 4, . . . . In addition, modems (modems) 5, 5, . , or converting the digital signal transmitted from the slave station 2 into an analog signal for the communication line, or conversely, playing the role of converting the analog signal coming over the communication line back into a digital signal, as in the past. Thus, in the present invention, at least each of the slave stations 2, 2, . FIG. 2 shows a detailed circuit diagram thereof. Since each slave station has the same configuration, to explain one of them, the CPU 6 built in the slave station 2 is connected to the branch line 4,
A carrier detection circuit 7 is installed between the dedicated trunk line 3 and the CPU 6 as a bypass circuit. The carrier detection circuit 7 detects the voltage between the dedicated main line 3 and the CPU 6 when a communication trigger is applied to the slave station 2,
The wiring is such that it is determined whether the dedicated main line 3 is already in use or not based on the voltage.

Note that various configurations other than those described above are conceivable as the carrier detection means, but these are omitted here. Furthermore, in this embodiment, in the middle of the wiring between the carrier detection circuit 7 and the CPU 6,
A waiting circuit 9 is interposed as a logic for removing the synchronization between each slave station 2, 2, . The dedicated main line 3 is configured to be on standby until the dedicated trunk line 3 becomes vacant due to the operation of a timer. Furthermore, each slave station 2, 2...
- A collision detection circuit 8 for detecting a contention for the dedicated trunk line 3 between the two is connected between the dedicated trunk line 3 and the CPU 6 in parallel with the carrier detection port 7; Also, the waiting circuit 9 is relayed in the middle of the wiring between the collision detection circuit 8 and the CPU 6. As a result, when a plurality of slave stations transmit carriers to the dedicated trunk line 3 at the same time, the collision detection circuit 8 and the waiting circuit 9 are activated, and the transmission rights of the dedicated trunk line 3 are subsequently controlled. It is considered.

However, when performing data communication using the data communication line configured in this way, when a communication trigger is applied to the master station 1 from the slave station 2 side, the carrier detection circuit 7 detects whether the dedicated main line 3 is used by another slave station. It is detected whether the If it is determined that the slave station 2 is not in use, the line is connected between the slave station 2 and the master station 1.
It becomes possible to communicate. Therefore, according to this data communication line system, the master station 1 and each slave station 2, 2...
There is no need to introduce a polling/selecting method between the two, and smooth communication can be achieved. Although not shown, a carrier detection means similar to that described above may be provided on the main station 1 side of the dedicated trunk line 3 as well. By doing so, in a communication line system in which communication between slave stations 2, 2 is possible, from the master station 1 to each slave station 2, 2...
On the other hand, it is effective for checking whether the dedicated trunk line 3 is being used when communication is desired.

[Effect of the invention] As is clear from the above description of the embodiments,
According to the slave-initiated data communication line system of the present invention, if the dedicated trunk line is not in use, the slave station can immediately become ready for communication by pressing a communication trigger. This eliminates the long access time required for applications that use the polling/selecting method, resulting in a smooth communication system and a significant improvement in line usage efficiency.Also, the polling/selecting method is not required. This also contributes to lower equipment costs by acclimating the equipment.

[Brief explanation of the drawing]

FIG. 1 is a schematic circuit diagram of a data communication line system according to the present invention, FIG. 2 is an electrical block diagram of the main part thereof, and FIGS. 3 and 4 are schematic circuit diagrams of a conventional data communication line system. 1...Main station, 2,2...Slave station, 3...Dedicated trunk line,
4, 4... Branch line, 7... Carrier detection circuit.

Claims (1)

[Claims] In a data communication line in which a master station that transmits data and a plurality of slave stations that receive data are connected to each other by a dedicated main line and a plurality of branch lines branching from the main line, at least on the side of each slave station, A slave station-initiated data communication line system, comprising carrier detection means for detecting whether the dedicated trunk line is being used by another slave station.