JPS60203035A - Bidirectional communication system using burst type code string - Google Patents

Abstract

PURPOSE:To prevent the generation of circuit distortion, by using the detection output of code polarity sent from a transmission line to control the polarity of an output code. CONSTITUTION:A polarity detecting circuit 30 is provided at the reception output of at least one of two circuit terminators 1 and 2, i.e., the terminator 2 which are set at both ends of a 2-wire transmission line 3. The circuit 30 detects the polarity of the last bit of a reception signal code string in response to the actuation of a transmission/reception switch circuit 29 when the reception state of the circuit 30 is changed to a transmission state. Then the circuit 30 controls a code converter circuit 24 so that the polarity of the minimum bit of a transmission signal code string is coincident with an AMI code rule.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a digital communication system using a two-wire transmission line. In particular, the present invention relates to an AMl code transmitting device of a transmitting device, which is a method of bidirectionally transmitting burst signals using a two-wire transmission path. Here, AMl code (Automati
c Mark Inversion Code)
It is a code configured such that the polarity is reversed between positive and negative for each "1" of the binary code, and the energy component thereof is concentrated on 1/2 of the transmission lock frequency (11).

[Description of prior art]

In such a conventional device, both line termination devices installed at both ends of a two-wire transmission line perform code transmission under control so that only their own transmission code strings satisfy the AMI code rules. Therefore, it is fine if burst signals of sufficiently long duration are transmitted from both line termination devices that sandwich a two-wire transmission line, but if short burst signals are sent and received alternately,
The AMI code rules are not necessarily satisfied between the two-way transmission code strings. In the conventional device, when the receiving state is switched to the transmitting state, the polarity of the first transmitted code is determined by a chance factor.

Since the two-wire transmission line on which the AMI code string is transmitted is a transmission system in which the low frequency is attenuated between the line terminal equipment, the transmission waveform distortion due to the attenuation of the low frequency does not satisfy the AMI code rule. If not, they will be added, increasing waveform distortion of the received code and causing deterioration of transmission characteristics.

[Purpose of the invention]

The present invention improves this and aims to provide a system that satisfies the AMI code rule between burst codes even when the transmission direction of the signal is reversed by switching between transmission and reception.

[Features of the invention]

In the present invention, at least one of two line termination devices installed at both ends of a two-wire transmission line is provided with a detection circuit for detecting the polarity of a code received from the transmission line, and the detection output of this detection circuit is used to control transmission and reception. The present invention is characterized in that it includes circuit means for generating an output code string in which the code string on the transmission path satisfies the AMI code rules before and after switching.

[Explanation based on examples]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. A two-wire transmission line 3 is connected between the line termination devices 1 and 2. The line termination device 1 includes a signal input terminal 11 and a signal output terminal 12. The signal at the signal input terminal 11 is converted into an AMI code by the code conversion circuit 14, a balanced code from the balanced code circuit 15 is inserted, and the signal is transmitted from the transmitting circuit 16 to the transmission line 3 via the transformer 17. In the line termination device 2, the transmission line 3 is connected to a transformer 27, and the receiving power is sent from the receiving circuit 28 to the receiving output terminal 22. Similarly, the signal input terminal 21 of the line termination device 2
The signal is converted into an AMI code by the code conversion circuit 24, a balanced code from the balanced code circuit 25 is inserted, and the signal is transmitted from the transmitting circuit 26 to the transmission line 3 via the transformer 27. In the line termination device I, the transmission line 3 is connected to a transformer 17, and its reception input is sent from a reception circuit 18 to a reception output terminal 12. The transmission line 3 is a two-wire line, and signals cannot be transmitted from both directions simultaneously. For this reason, the line termination device 1 is equipped with a control signal terminal 13 to which a transmission/reception switching control signal is manually input, and the transmission/reception switching circuit 19 enables the transmission circuit 16 and the reception circuit 18 alternately according to the logical value of this control signal. . On the other hand, line termination device 2
Based on the received signal output obtained from the receiving circuit 28, the transmission/reception switching circuit 29 enables the receiving circuit 28 when the burst signal is arriving, and enables the transmitting circuit 26 when the burst signal is interrupted.

Here, the feature of the present invention is that a polarity detection circuit 30 is provided at the received signal output of the line termination device 2, and the polarity of the output code of the code conversion circuit 24 is controlled by this detection output. be.

That is, the polarity detection circuit 30 detects the polarity of the last bit of the received signal code string when switching from the reception state to the transmission state according to the operation of the transmission/reception switching circuit 29,
The code conversion circuit 24 is controlled so that the polarity of the smallest bit of the transmission signal code string matches the AMI code rule.

FIG. 2 is a diagram illustrating a signal code string of this transmission line 3. Figure 2A is the waveform at end A of transmission line 3 shown in Figure 1, and waveform B
Similarly, shows the waveform at the B end. The part surrounded by a broken line is one burst signal, and the arrow indicates the transmission direction. That is, the burst signal a1 propagates through the transmission line 3 and becomes the burst signal b1.

At the next timing, the burst signal b2 moves from the B end to the A
It is transmitted to the end and becomes a burst signal a2.

In this way, burst signals are transmitted alternately. The bit added at the end of the burst signal outside the dashed line is a balanced code, which is the code generated by circuits 15 and 25.

Here, as shown with diagonal lines in Figure 2, if we look at the polarities of the last bit and first bit of each burst signal propagating to the transmission path, they are always reversed alternately and satisfy the AMI sign rule. It is configured as follows.

FIG. 3 is a diagram illustrating a signal code string of a conventional device shown as a comparative example. In this case, each code conversion circuit does not control the polarity of the first bit of the burst signal, so the polarity of the last bit of each burst signal and the first bit of the next burst signal is not necessarily the same. It is exemplified that it is not inverted and does not satisfy the AMI sign rule.

In the above example, the polarity detection circuit 30 is provided only in the line termination device 2 to control the polarity of the transmission code string of the code conversion circuit 24. However, a polarity detection circuit is provided in both the line termination devices at both ends, and each It is also possible to control the polarity of the transmission code string.

〔Effect of the invention〕

As explained above, according to the present invention, the code string transmitted to the transmission line satisfies the AMI code rule even before and after switching between transmission and reception, so there is no addition of DC signal components, and therefore line distortion will never occur. The present invention is extremely effective in devices that transmit bidirectional signals by frequently switching short burst signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a waveform diagram for explaining the operation of the device according to the embodiment of the present invention. FIG. 3 is an operation waveform diagram of a conventional device shown as a comparative example. 1.2... Line termination device, 3... Bidirectional transmission line by two-wire line, 11.21... Transmission signal input terminal, 12
．． 22... Reception signal output terminal, 13... Transmission/reception switching control signal terminal, 14.24... Code conversion circuit, 15.2
5...Balanced code circuit, 16.26...Transmission circuit, 1
8.28...Reception circuit, 30...Polarity detection circuit. Patent applicant Naotaka Ide, patent attorney representing Nippon Telegraph and Telephone Public Corporation

Claims (1)

[Claims] (1) A two-wire transmission line and a line termination device installed at both ends of the two-wire transmission line, the two-wire transmission line is composed of a line with large attenuation of the DC component of the signal, and the line termination devices at both ends are connected to the two-wire transmission line. The line termination device includes switching means for synchronously switching between transmission and reception so as to alternately transmit and receive burst-like code strings via the line transmission path, and each of the line termination devices converts the input signals to be transmitted according to the AMI code rules. In the bidirectional communication system using a burst-like code string, which is equipped with a code conversion means for transmitting a code, at least one of the line termination devices is provided with a detection circuit for detecting the polarity of the code received from the transmission path, and the code conversion The means detects that the code string on the transmission path is AM by the detection output of the detection circuit before and after switching between transmission and reception.
1. A bidirectional communication system using a burst-like code string, characterized by comprising circuit means for generating an output code string that satisfies the I code rule.