JPH0237148B2 - DEETADENSOSHISUTEMU - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a data transmission system, and particularly to a data transmission system between a host computer and each control device for realizing factory automation. .

[Background Art] As such a data transmission system, a system using a transmission method consisting of a single signal in which a clock is extracted from the signal is known.

For example, the NRZI method is one example.

An advantage of this system is that it has a small number of signal lines, so it is advantageous in terms of cost when the distance between stations is long.

The NRZI method is detailed in JP-A-55-89912 and JP-A-57-132461, so I will omit it here, but in a transmission system using this method, a demodulation circuit (for example, a PLL circuit) is installed in the receiving section of every station. The problem is that it is necessary.

When a station (also called a module) 2 is connected to a transmission line 1 as shown in FIG.
A specific example of the circuit is shown in FIG.

In FIG. 2, 4 is a PLL demodulator, which must be provided for each station 2.

In other words, when the distance between stations is short, the cost of the demodulation circuit increases rather than reducing the cost by reducing the number of signal lines.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a data transmission system that connects stations efficiently and at low cost.

[Summary of the invention]

The gist of the present invention is to configure a data transmission system in which a general and inexpensive clock and data are sent in parallel between lower stations, and to install an interface module that connects these lower stations with an upper transmission line. The point is that I decided to share it.

[Embodiments of the invention]

Hereinafter, specific examples of the present invention will be described.

FIG. 3 is a block diagram illustrating the concept of the present invention.

1 is an upper transmission line, and a transmission signal (NRZI system, Manchester system, etc.) in a format that allows the clock to be extracted from the signal is sent.

2 is a station, 3 is a lower transmission line, and 4 is an interface module.

FIG. 4 shows a specific circuit example of the present invention, in which a half-duplex bus system is used.
The specific operation will be explained using FIG. 4.

From the main station (data transmitting station), upper transmission line 1
When a signal is sent through the line driver 4-a, the line driver 4-a inputs data to the PLL circuit 4-b.

The PLL circuit 4-b extracts the clock from the signal and passes it through the gate 4-c to the lower transmission line 3-c.
It sends out a clock to the lower transmission line 3-b through the gate 4-d, formats the data, and sends the data to the lower transmission line 3-b. Secondary station (data receiving station) 2
import into RXD. At this time, the lower transmission line 3-c is "H". When the secondary station 2 finishes inputting data and issues a response signal,
Output the SEND signal and set the lower transmission line 3-c to "L".

This closes the gate 4-d, and the PLL circuit 4
-b becomes FREE RUN and sends a predetermined transmission clock to the lower transmission line 3-a.

Transmission data TXD from the secondary station is outputted to the lower transmission bus 3-b by this clock, and then sent to the upper transmission line 1 through the activated line driver 4-e.

In this way, the upper and lower transmission lines are connected.

Note that the upper transmission line may be composed of an optical fiber cable, and the lower transmission line may be composed of a flat cable or the like.

In other words, by storing multiple stations in one board,
If each panel is equipped with one demodulator, the panels can be connected by optical fiber cables and the panels can be connected by flat cables.

〔Effect of the invention〕

As described above, according to the present invention, an expensive demodulator (PLL circuit) can be shared by multiple stations, so
A data transmission system that is low cost, efficient, and highly flexible can be obtained.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a conventional example, FIG. 2 is a circuit diagram of a conventional example, FIG. 3 is a conceptual diagram of the present invention, and FIG. 4 is a specific embodiment of the present invention.

Claims (1)

[Scope of Claims] 1. An upper level transmission system is constructed using a single signal data transmission system in which a clock can be extracted from a signal, and a lower level transmission system is constructed using a data transmission system in which data and clocks are sent in parallel. A transmission system is configured, the transmission line of the upper transmission system and the transmission line of the lower transmission system are connected via a demodulation section, each of the lower stations shares the demodulation section for each plurality of stations, and the demodulation section includes: It bidirectionally converts between a single signal data format and a format in which data and clocks are sent in parallel, and stops sending data from the upper side to the lower transmission line in response to a transmission request signal issued by each lower station. A data transmission system characterized in that the demodulator sends a clock to the lower transmission line even during the stop period, and each lower station uses this as a transmission clock.