JPH01260949A - Collision detection circuit - Google Patents

Abstract

PURPOSE:To accurately detect collision even if a level change at collision is very small by differentiating a signal on a transmission medium so as to detect a change point and ANDing the point with a change point based on a prescribed signal sent from a terminal equipment. CONSTITUTION:When a terminal equipment 2-2 sends a signal B from a driver 5-2, signals A, B are collided with each other on the transmission medium 1 near the terminal equipment 2-2 to generate a signal C received by a receiver 4-2 and the collision is detected by a collision detection circuit 6-2. The signal C is differentiated by a differentiating circuit 62 and given to one input of an AND circuit 63. An input signal to the driver 5-2 is given to the other input of the AND circuit 63 as the gate signal and a short pulse of a change point based on the output signal from the driver 5-2 of the terminal equipment 2-2 is eliminated. Thus, the presence of collision between signals is detected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a circuit that detects collisions between signals on a single transmission medium to which a plurality of terminal devices are connected.

(Prior art) A plurality of terminal devices are connected to a single transmission medium, and communication is performed between arbitrary terminal devices or between an arbitrary terminal device and an arbitrary plurality of other terminal devices. Figure 2 shows an overview of the system.

In Figure 2, 1 is one transmission medium, 2~1.2-2
is a terminal device (DTE), the terminal device 2-1 is connected to the transmission medium 1 via the driver 3-1 and the receiver 4-1, and the terminal device 2-2 is connected to the transmission medium 1 via the driver 3-2 and the receiver 4-1. -2 to the transmission medium 1. In addition, although multiple terminal devices are actually installed,
Only two of them are shown here.

Usually, the driver 3-1.3-2 includes rI E
As stated in "EE Standard 802.3, CSMA/CD Access Method and Physical Layer Specifications" (Published by Japan Electronics Industry Promotion Association, pp. 115-117.1983), those with high output impedance are used. On the other hand, as the transmission medium 1, a medium with a numerically low characteristic impedance is used in order to ensure broadband characteristics of the transmission line.

In the above configuration, the terminal device 2-1 sends the signal a shown in FIG. 3 to the driver 3-1 to another terminal device (not shown).
It is assumed that the data is sent to the transmission medium 1. At this time, the terminal device 2-2 sends the signal shown in FIG. 3 to the driver 3-2.
2 to the transmission medium 1, the signal a and the signal S collide on the transmission medium 1 near the terminal device 2-2. At this time, since the level of signal a and the level of signal A signal C occurs.

The signal C is received by the receiver 4-2 of the terminal device 2-2 and binarized using a predetermined threshold voltage VTR, resulting in a signal d as shown in FIG. The signal d differs in pulse width, pulse transition point, etc. from a signal when there is no collision between signals on the transmission medium 1 (usually a signal having the same waveform as the signals a and b). Therefore, collisions between signals in this case could be easily detected by checking the sign rule.

(Problem to be Solved by the Invention) However, in the above configuration, since the output impedance of the drivers 3-1 and 3-2 is high, an impedance mismatch occurs between the drivers 3-1 and 3-2 and the transmission medium 1 having a low characteristic impedance. 1.3-2 has a problem in that the drive efficiency is poor and it is difficult to drive a balanced transmission medium that is resistant to externally induced noise as the transmission medium 1.

On the other hand, in order to solve the problem, the driver 3-1
．． As 3-2, it is also possible to use a device with low output impedance during signal transmission. In this case, similarly to the above, the terminal device 2
When the signal a sent from the terminal device 2-1 collides with the signal a sent from the terminal device 2-2, the voltage of the signal a is divided because the output impedance of the driver 3-2 is low.
A signal e as shown in the figure is generated.

By the way, the signal e has a threshold voltage V at the receiver 4-2.
When binarized at T11, the signal f as shown in FIG.
becomes. Since the waveform of this signal f is almost the same as the waveform of the output signal S of the driver 3-2 of the terminal device 2-2, there is a problem in that it is difficult to detect collisions between the signals.

An object of the present invention is to eliminate the above-mentioned problems and provide a circuit that can reliably detect signal collisions using a low output impedance driver that has high drive efficiency and is easy to drive a balanced transmission medium. be.

(Means for Solving the Problem) In order to achieve the above object, the present invention connects a plurality of terminal devices each having a driver with a low output impedance when transmitting a signal to a single transmission medium with a low characteristic impedance,
In a system that performs communication between arbitrary terminal devices or between an arbitrary terminal device and arbitrary plurality of other terminal devices, each terminal device is equipped with a differentiating circuit that differentiates a signal on a transmission medium. , an AND circuit that takes an AND of an input signal to the driver and the output of the differentiating circuit, and a determination circuit that determines whether or not there is a collision between signals on the transmission medium based on the output signal of the AND circuit. Established.

(Function) According to the present invention, a terminal device that sends a predetermined signal to another terminal device uses a differentiation circuit to differentiate a signal on a transmission medium and detects a change point thereof, and further uses an AND circuit to differentiate a signal on a transmission medium and detect a change point thereof. The change point based on the transmitted predetermined signal and the detected change point are logically ANDed, and the change point based on the transmitted predetermined signal is removed from the detected change point. If no other signal is flowing on the transmission medium, the AND circuit will not output anything, and therefore the judgment circuit will judge that there is no collision between the signals.Also, if another signal is flowing on the transmission medium, The AND circuit outputs a change point based on the other signal, and the determination circuit therefore determines that there is a collision between the signals.

(Embodiment) FIG. 1 shows an embodiment of the collision detection circuit of the present invention, and in the figure, the same components as those of the conventional example are denoted by the same reference numerals. That is, 1 is the transmission medium, 2-1.2-2 is the terminal device (
DTE), 4-1.4-2 is the receiver, 5-1.5-
2 is Drino (, 6-1, 6-2 are collision detection circuits).

The drivers 5-1 and 5-2 are for sending signals from the terminal devices 2-1 and 2-2 to the transmission medium 1, respectively, and their output impedance is always high, and the output impedance is high only when sending signals. Control circuits (not shown) in the terminal devices 2-1 and 2-2 control the impedance to be low.

The collision detection circuits 6-1 and 6-2 detect collisions of signals on the transmission medium 1. Figure 4 shows the configuration of the collision detection circuit 6-2 (6-1 is also the same), in which 61 is a differential amplifier, 62 is a differentiation circuit, 63 is an AND circuit, and 64 is a judgment circuit. .

The input terminal of the differential amplifier 61 is connected to the transmission medium 1 and extracts the signal generated on the transmission medium 1.

Further, the output of the differential amplifier 61 is input to the differentiating circuit 62, and the changing points in the signal are extracted. The output of the differentiating circuit 62 is connected to one input terminal of the AND circuit 63, and the input signal to the driver 5-2, that is, the transmission data, is input to the other input terminal. It looks like it's outputting. Further, the determination circuit 64 is, for example, a well-known rectifier circuit, a monostable multivibrator, or an integrating circuit.

It consists of a level detection circuit and the like, rectifies the output of the AND circuit 63, extends its pulse width, compares the integrated signal with a predetermined threshold, and outputs the result.

Next, the operation will be explained according to FIG. 5 showing waveforms of each part.

In the above configuration, the terminal device 2-1 sends the signal A shown in FIG. 5 to the driver 5-1 to another terminal device (not shown).
It is assumed that the data is sent to the transmission medium 1. At this time, the terminal device 2-2 transmits the signal B shown in FIG.
2 to the transmission medium 1, the signals A and B collide on the transmission medium 1 near the terminal device 2-2.

At this time, the output impedance of the driver 5-2 is set low by the control signal input to its control terminal C0NT, so the voltage of the signal A is divided, and the voltage on the transmission medium 1 near the terminal device 2-2 is A signal C as shown in FIG. 5 occurs. The signal C is received by the receiver 4-2 of the terminal device 2-2, and a collision is detected by the collision detection circuit 6-2.

That is, the signal C is received from the transmission medium 1 by the differential amplifier 61, sent to the differentiation circuit 62, and differentiated there.
As shown in FIG. 5, a signal having short pulses corresponding to all the changing points is generated and is input to one input terminal of the AND circuit 63.

Note that since the differentiating circuit 62 is a circuit with a large gain for signals that change rapidly, there is actually no level difference as shown in each short pulse of the signal, but here, the signal C
It is shown to make it easier to understand the correspondence relationship.

Further, the other input terminal of the AND circuit 63 is connected to the driver 5.
-2 input signal is input as a gate signal, and the short pulse at the change point based on the output signal from the driver 5-2 of the terminal device 2-2 is removed by ANDing this gate signal and the above-mentioned signal. The signal E shown in FIG. 5 is obtained.

The signal E is input to the determination circuit 64, where each of the short pulses is rectified and converted into a pulse of a predetermined width, and further integrated.
The level is determined between a predetermined threshold value. At this time, if the integrated signal level is above the threshold value, it is determined that there is a collision between the signals, and if it is below the threshold value, it is determined that there is no collision between the signals. The corresponding signal level is determined to be a collision.

Further, if there is no output signal from the driver 5-1, no short pulse in the signal E is generated at all, and therefore, it is determined that there is no collision at this time.

The terminal device 2-2 receives the determination result and, for example, if there is a collision between the signals, temporarily stops transmitting the signal from the driver 5-2, and after a predetermined time, transmits the signal from the driver 5-2 again. Performs control such as sending.

In this way, according to the embodiment, since a differentiating circuit is used which is highly sensitive to changing points, even changing points where the level change is small can be converted into short pulses. Therefore, changing points caused by collisions between signals can be converted into short pulses. Based on this, it is possible to accurately detect whether there is a collision between signals.

In addition, in the above embodiment, the collision detection circuit 6-1.6-
2 is directly connected to the transmission medium 1, but since the receiver 4-1.4-2 converts all its input signals into binary digital values, a differentiating circuit is connected to its output. This is also because changing points caused by collisions with other signals cannot be detected.

(Effects of the Invention) As explained above, according to the present invention, a change point is detected by differentiating a signal on a transmission medium, and a collision is detected based on a predetermined signal sent from a terminal device that attempts to detect a collision with the change point. The change point based on the transmitted signal is removed by performing a logical product with the change point, and the presence or absence of a collision between signals is determined from the remaining signals, so the output impedance of the driver is low and the level at the time of collision is low. Even if the change is small, it can be detected accurately and can be effectively used for detecting signal collisions in local area networks and the like.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram showing an embodiment of the collision detection circuit of the present invention, FIG. 2 is a diagram showing an outline of a conventional system, and FIG. 3 is a diagram showing signals in each part of FIG. FIG. 4 is a block diagram showing details of the collision detection circuit, and FIG. 5 is a signal waveform diagram at each part of FIGS. 1 and 4. 1... Transmission medium, 2-1.2-2... Terminal device, 4
-1.4-2...Receiver, 5-1.5-2...Driver, 6-1.6-2...Collision detection circuit, 62...
- Differentiation circuit, 63... AND circuit, 64... Judgment circuit. Patent applicant Oki Electric Industry Co., Ltd. Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] A plurality of terminal devices each having a driver with low output impedance when transmitting a signal to a single transmission medium with low characteristic impedance are connected, and a plurality of terminal devices are connected to each other, or between any one terminal device, or between any one terminal device. In a system that performs communication between a terminal device and a plurality of arbitrary other terminal devices, each terminal device includes a differentiating circuit that differentiates a signal on a transmission medium, and a logical product of the input signal to the driver and the output of the differentiating circuit. What is claimed is: 1. A collision detection circuit comprising: an AND circuit that takes the following equation; and a determination circuit that determines whether there is a collision between signals on a transmission medium based on the output signal of the AND circuit.