JPH01296839A - Data transmission system - Google Patents

Abstract

PURPOSE:To correctly transmit data through many data transmitting devices by providing a means to correct the expansion of the waveform to occur by the signal processing part in a data transmission line and a data transmitting device. CONSTITUTION:In this example, the delay of t1-t0 occurs at the rise of a signal and at the fall of the signal, the delay of t4-t3 occurs. First, an output (b) of a receiving circuit 11 rises at the timing of the t1, and thus, a synchronizing clock signal generating circuit 13 synchronizes to this and generates a clock signal. A D type FF12 becomes active at a rise timing t2 of a clock signal and holds the condition of a D input. Thereafter, since (b) is an L level at the time of a next rise timing t5 of the clock signal, a Q output (d) of an FF12 becomes an L level. Hereinafter in the same way, for an output signal (b) of a receiving circuit, the expansion of the time base direction is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Al Industrial Application Field) This invention relates to a data transmission system using a data transmission line such as an optical fiber.

(bl Conventional technologyAs a system for transmitting predetermined data within a predetermined system,
Conventionally, various data transmission systems have been constructed.

As a transmission line used in such a data transmission system, a coaxial cable, twisted pair cable, optical fiber cable, or the like is used depending on the scale of the system, data transmission speed, etc. In addition, when data is transmitted over a relatively long distance, an amplifier circuit or a waveform shaping circuit is provided to correct signal attenuation caused by the cable and waveform distortion caused by this attenuation (C) Invention However, in a data transmission system in which multiple data transmission devices are connected in series at a certain interval via a data transmission path, due to the effects of the amplifier circuit and waveform shaping circuit installed in the data transmission device, There is a problem in that the expansion and contraction of the waveform in the time axis direction is cumulative. Particularly when using cheap and easy-to-handle plastic fiber as a data transmission path, the data transmission distance is 100% due to effects such as optical attenuation.
However, when performing medium-distance data transmission by connecting terminals and repeaters within a range not exceeding 100 m, the accumulation of waveform expansion and contraction becomes a serious problem.

For example, as shown in FIG. 3, consider a case where a plurality of data transmission devices 2 to 7 are connected in series to a controller 1 that transmits data via a data transmission path made of plastic optical fibers. Each of the terminals 2, 3, and 4.7 is equipped with means for amplifying the signal received from the data transmission path, shaping the waveform, and transmitting the signal to a subsequent terminal, etc., and reading the necessary signal as data. Note that the repeater 5.6 is provided to relay the signal transmitted from the terminal 4 to the terminal 7.

4 and 5 show examples of waveform expansion at the terminals and repeaters shown in FIG. 3 and waveforms at various positions on the data transmission path.

As shown in Figure 4, compared to the signal (a) inside the terminal or repeater on the transmitting side, the received signal on the receiving side (bl is the light emitting element on the transmitting side, the light receiving element on the receiving side, the amplifier circuit, etc.) Due to the characteristics of the waveform, there is a delay of T1 in the rising part and T2 in the falling part.In this example, since the relationship is Tl<T2, the "H" level period of the waveform is extended. .

FIG. 5 illustrates the cumulative effect of such waveform expansion and contraction, where (al~(el is (al~(e
) shows the waveform of the transmission signal of each data transmission device. As shown in the figure, each time the waveform passes through a data transmission device such as a terminal or repeater, the ■]°“ level section of the waveform is cumulatively expanded. As a result, terminals connected far from the controller may read incorrect data. That will happen.

The purpose of the present invention is to provide a data transmission system that can correctly transmit data even through a large number of data transmission devices by correcting waveform expansion and contraction caused by data transmission paths and signal processing units in data transmission devices. It is about providing.

(Means for Solving Problem d1) This invention connects a plurality of data transmission devices each having a means for transmitting part or all of a received signal as is to a succeeding data transmission device in an asynchronous transmission method, by connecting a data transmission path. In a data transmission system connected in series through a synchronous clock signal generating means that generates a clock signal in synchronization with a received signal, and a D-type clock signal generating means that maintains the state of the received signal at the timing of this clock signal until the timing of the next clock signal. (e) A flip-flop is provided in each data transmission device.

The data transmission system of the present invention includes a synchronous clock signal generating means that generates a clock signal in synchronization with a received signal, and a D-type flip-flop that maintains the state of the received signal at the timing of the clock signal until the timing of the next clock signal. A loop is provided in each data transmission device. Therefore, a signal obtained by synchronizing the received signal with a clock signal appears at the output of the above-mentioned flipflop, and since the period of this clock signal is equal on the transmitting and receiving sides, the original waveform without expansion or contraction is reproduced.

(f) Embodiment FIG. 1 shows a block diagram of main parts of a data transmission system such as terminals or repeaters in a data transmission system to which the present invention is applied. In the figure, 10 is an input side data transmission line made of optical fiber, and a receiving circuit 11
receives an optical signal, performs photoelectric conversion, and generates a logic level voltage signal. 12 is a D-type flip-flop;
The output signal ('b) of the receiving circuit 11 is connected to the input terminal, and the Q output is outputted to the transmitting circuit 14. The synchronous clock signal generation circuit 13 receives the output signal (bl
A clock signal (C1) is generated to the D-type flip-flop 12 in synchronization with the rising edge of C1 and with a delay of half a bit.

The transmitting circuit 14 receives the output signal of the D-type flip-flop 12 (
dl is converted into an optical signal and output to a data transmission line 15 made of an optical fiber.

FIG. 2 is a diagram showing the operation timing of each part of the circuit shown in FIG. 1, and (bl to (d) are (b) shown in FIG.
~td). Further, (a) shows an output signal from a data transmission device such as a terminal or a repeater connected upstream of the data transmission device shown in FIG. 1 via the transmission line 10.

As shown in Figure 2, in this example, at the rising edge of the signal, t
The l-to delay is t4-t at the falling edge of the signal.
3 delays have occurred. First, as the output (b>) of the receiving circuit 11 rises at timing tl, the synchronous clock signal generating circuit 13 generates a clock signal in synchronization with this. It becomes active and maintains the state of the D input.At this time, the D input (bl is “°H”)
level, the "H'" level is held and the Q output (
d3 becomes "HII." After that, at the next rising timing t5 of the clock signal, since tb> is "L" level, the Q output (d) of the D-type flip-flop 12
becomes the "L I+ level. Furthermore, at the next rising timing t7 of the clock signal, the D input (1)) of the D-type flip-flop is at the "HII level, so the Q output (
d) becomes the "'H" degree level. Thereafter, in the same way, the expansion and contraction in the time axis direction of the output signal δ[b] of the receiving circuit is corrected by a D-type flip-flop (a waveform similar to the original waveform shown in al is obtained).

Note that the synchronous clock signal generation circuit 13 receives the received signal (b)
Since the synchronization is performed each time the clock signal rises (tl, t6. tlO), etc., it can be accurately corrected if the waveform expansion/contraction of the received signal is less than half a bit (half cycle yIJ1) of the clock signal.

(g) Effects of the Invention As described above, according to the present invention, the transmission data waveform may be affected by the response delay due to the characteristics of the light receiving element, amplifier circuit, waveform shaping circuit, etc. in the receiving circuit, and the response characteristics of the light emitting element in the transmitting circuit. Even if expansion or contraction occurs in the time axis direction, the waveform is corrected in synchronization with the basic clock signal, so even if many terminals, repeaters, or other data transmission devices are connected in series via a data transmission path, the waveform The expansion and contraction of data is not accumulated, making it possible to transmit data accurately. Therefore, a medium-distance data transmission system can be easily constructed using, for example, a plastic optical fiber that is inexpensive and has good workability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts in a data transmission device in a data transmission system to which the present invention is applied;
The figure is a diagram showing the operation timing of each part in FIG. 1. FIG. 3 is a diagram showing an example of a data transmission system configured by connecting a large number of data transmission devices. FIG. 4 is a diagram illustrating an example of waveform expansion caused by transmission between data transmission devices, and FIG. 5 is a diagram illustrating waveform changes according to a conventional technique that does not correct waveform expansion/contraction. 10.15-Data transmission line, 12-D type flip-flop.

Claims (1)

[Claims] (1) In a data transmission system in which a plurality of data transmission devices are connected in series via a data transmission path, each having means for transmitting part or all of a received signal as is to a subsequent data transmission device using an asynchronous transmission method, Each data transmission device is provided with a synchronous clock signal generation means for generating a clock signal in synchronization with a received signal, and a D-type flip-flop that maintains the state of the received signal at the timing of this clock signal until the timing of the next clock signal. . A data transmission system, wherein the D-type flip-flop corrects waveform expansion and contraction of a received signal.