JP3402352B2 - Repeater - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a repeater that relays a signal received from a communication bus and sends the signal to the communication bus. More specifically, the present invention relates to a repeater designed to prevent erroneous transmission.

[0002]

BACKGROUND OF THE INVENTION Repeaters are used to extend communication distance. LAN (Local Area Network)
In a communication system such as the above, an optical repeater is used as a repeater. An optical repeater is a repeater of optical signals.

FIG. 5 is a diagram showing a configuration example of a conventional optical repeater. In FIG. 5, 1 is a communication bus, and 2 and 3 are receiving circuits for receiving signals sent from the communication bus 1. The communication bus 1 is a bus for transmitting an optical signal and is composed of, for example, an optical fiber. The reception circuits 2 and 3 output a reception detection signal and reception data. Reference numerals 4 and 5 denote relay circuits that perform a relay operation by receiving the reception detection signal and the reception data, and reference numerals 6 and 7 denote transmission circuits that send the reception data after the relay to the communication bus 1.
Each of the transmission circuits 6 and 7 has a light emitting element such as an LED, converts an electric signal received from the relay circuits 4 and 5 into an optical signal, and sends the optical signal to the communication bus 1. Two receiver circuits, two relay circuits, and two transmitter circuits are provided for bidirectional communication.

FIG. 6 is a diagram showing a configuration example of the receiving circuits 2 and 3. In FIG. 6, A1 is an amplifier, and a photodiode D is connected to the input stage. When the photodiode D receives an optical signal from the communication bus 1, the amplifier A1 outputs an electric signal corresponding to the received optical signal. C is amplifier A1
This is a capacitor for removing the DC component of the output of. A2 is a data identification circuit, which compares the level of the signal after passing through the capacitor C with the reference voltage Vr and outputs a binary signal according to the comparison result. The data identification circuit A2 identifies a voltage signal higher than the reference voltage Vr as communication data and outputs it. A3
Is an amplitude discrimination circuit, which compares the amplitude of the signal after passing through the capacitor C with a predetermined reference value, and outputs a reception detection signal according to the comparison result. When the amplitude of the signal after passing through the capacitor C is larger than the reference value, the reception detection signal is turned on, and when it is small, it is turned off. The amplitude identification circuit A3 is composed of, for example, a peak detection circuit and a comparator.

The communication of optical signals mainly aims to extend the communication distance. Therefore, there is a demand to increase the dynamic range of the receiving circuit so that even an attenuated optical signal can be received. When the dynamic range of the receiving circuit is increased, a change in signal level caused by offset or drift of the receiving circuit may be erroneously detected as received data. In order to avoid this, the capacitor C is connected to the output stage of the amplifier A1 to remove the DC component. As a result, it is not permissible to keep the signal level constant even when there is no transmitted data. Therefore, even when there is no transmission data, a dummy signal called a pseudo silence signal that changes at a constant cycle is continuously sent.

However, the conventional examples shown in FIGS. 5 and 6 have the following problems. If the reception detection signal is an incorrect signal, noise may be mistakenly recognized as communication data and relayed, or correct communication data may be mistakenly recognized as noise and not relayed. That is, the reception detection signal cannot be trusted. Also,
Even when the amplitude detection circuit A3 is not provided and the reception detection signal is not given, an erroneous relay operation may be similarly performed.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and communication is provided by providing a circuit for monitoring a signal pattern that does not correspond to communication data or pseudo silence signal. It is an object of the present invention to realize a repeater that can correctly identify and relay data.

[0008]

The present invention is a repeater configured as follows. (1) In a repeater that relays a signal received from the communication bus and sends it to the communication bus, when the received data received from the communication bus changes a predetermined number of times or more within a predetermined time , a normal communication is performed.
Data detection means for identifying that the received data has been detected, turning on the data detection signal, and turning it off in other cases, and starting counting when the data detection signal is turned on, and turning it off It is reset and normal communication data
The counter that measures the time that the counter continues, the comparing means that compares the count immediately before the counter is reset with a predetermined value, and the result of the comparison by the comparing means is that the count immediately before the counter is reset. When the value is larger than a predetermined value, a determination signal indicating that the received data is valid is output, and when the value is smaller than the predetermined value, a determination unit that outputs a determination signal indicating that the received data is invalid, A repeater comprising: (2) The repeater according to claim 1, wherein the predetermined value is a minimum communication frame length.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.
In FIG. 1, the same parts as those in FIGS. 5 and 6 are designated by the same reference numerals.
Although only the configuration of the relay portion in one direction is shown in FIG. 1, the configuration of the relay portion in the opposite direction is also similar. In FIG. 1, reference numeral 20 is a monitoring circuit which is a feature of the present invention.
Based on the reception data and the reception detection signal received from the reception circuit 3, the signal pattern that does not correspond to the communication data or the pseudo silence signal is monitored.

FIG. 2 is a diagram showing a specific configuration example of the monitoring circuit 20. In FIG. 2, reference numeral 21 denotes a data detecting means which receives the received data and the received detection signal, discriminates the pseudo silence signal from other signals, and outputs a data detection signal indicating the discrimination result. The data detection means 21 identifies that a signal other than the pseudo silence signal is detected when the received data changes a predetermined number of times or more within a predetermined time while the reception detection signal is on, and the data detection signal is detected. Turn on. In other cases, the data detection signal is turned off. Normal communication data has a higher frequency than the pseudo silence signal. Some noise has a higher frequency than the pseudo silence signal. A counter 22 starts counting when the data detection signal is turned on and is reset when the data detection signal is turned off. The counter 22 measures the time during which signals other than the pseudo silence signal continue. Reference numeral 23 is a comparison means for comparing the count immediately before the counter is reset with a predetermined value. Reference numeral 24 is a one-shot circuit, and as a result of the comparison by the comparison means 23, when the count immediately before the counter 22 is reset is smaller than a predetermined value, an inhibition pulse is generated as the received data is invalid, and a predetermined value is generated. If it is larger than the above, the inhibit pulse is not generated because the received data is valid. An AND gate 25 outputs a determination signal which is the logical product of the data detection signal and the output of the one-shot circuit 24. Since the inhibit pulse is a low level signal,
When the inhibition pulse is issued, the data detection signal does not pass through the AND gate 25. The determination signal of the AND gate 25 becomes low level when the received data is invalid, and becomes high level when the received data is valid.

The operation of the repeater shown in FIGS. 1 and 2 will be described.
First, the operation during normal operation will be described. FIG. 3 is a time chart of each signal in a normal state. During normal operation, the reception detection signal is always on. The received data changes as shown in (a). The communication data has a higher frequency than the pseudo silence signal. When receiving the pseudo silence signal, the data detecting means 21 turns off the data detecting signal because the received data does not change more than the predetermined number of times within the predetermined time. When the communication data is received, the data detection signal is turned on because the received data changes a predetermined number of times or more within a predetermined time. When the communication data is received , the data detection signal turns on after a predetermined time , the counter 22 starts counting, and when the communication data ends , the data detection signal turns off after a predetermined time and the counter 22 is reset. At this time, the judging means 23 judges whether the count immediately before the counter 22 is reset is equal to or more than a predetermined value.
The predetermined value is, for example, the minimum communication frame length. In the illustrated example, the predetermined value is "8" and the count immediately before resetting is "12". Therefore, the received data is determined to be normal communication data, and the one-shot circuit 24 outputs the prohibition pulse. Instead, the monitoring circuit 20 outputs a determination signal that the received data is valid.

Next, the operation at the time of abnormality will be described. 4 is different
It is a time chart of each signal at all times. A case where an abnormality such as disconnection of the communication cable occurs and the reception detection signal is held on will be described. It is assumed that the received data changes almost randomly. Data detection means 21
Turns on the data detection signal when it detects a portion of the received data that changes a predetermined number of times or more within a predetermined time. The counter 22 starts counting at the rising edge of the data detection signal and is reset at the falling edge. Since the received data is a signal that changes from random to random, the count immediately before the counter 22 is reset does not become larger than a predetermined value. In the example in the figure, the count is "5",
It is smaller than the predetermined value "8". Therefore, the one-shot circuit 24 generates a prohibition pulse because the received data is invalid. As a result, the low-level determination signal is given to the relay circuit 5, and the fact that the received data is invalid is notified. The pulse width of the inhibit pulse (the time width of the low level portion) is sufficiently longer than the duration of the received data which changes almost randomly.

In the embodiment, the case where the communication bus is an optical signal bus has been described, but the communication bus may be an electric signal bus.

The monitoring circuit may have another structure. For example, a counter that counts the number of times the received data received from the communication bus changes within a predetermined time, a comparing unit that compares the count of this counter with a predetermined upper limit value and a lower limit value, and the result of the comparison of this comparing unit, When the count is larger than the upper limit value, or when the count is smaller than the lower limit value, a judging means for outputting a judgment signal indicating that the received data is invalid may be provided. In the monitoring circuit having such a configuration, for example, the pseudo silence signal is 1.25 Mbps (Mega bits).
per second), when the communication data has a transmission rate of 20 Mbps, it is abnormal when there are 1 × 2 ²⁰ or less data changes per second or 25 × 2 ²⁰ or more data changes per second. To determine.

[0015]

According to the present invention, since the circuit for monitoring the signal pattern which does not correspond to the communication data or the pseudo silence signal is provided, the communication data can be correctly identified and relayed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a main part of the repeater in FIG.

FIG. 3 is an operation explanatory diagram of the present invention.

FIG. 4 is an explanatory diagram of the operation of the present invention.

FIG. 5 is a diagram showing a configuration example of a conventional optical repeater.

6 is a diagram showing a configuration example of a receiving circuit of the optical repeater of FIG.

[Explanation of symbols]

1 communication bus A few receiving circuits 4, 5 Relay circuit 6,7 Transmitter circuit 20 monitoring circuit 21 Data detection means 22 counter 23 Judgment means 24 One-shot circuit 25 AND GATE

Claims (2)

(57) [Claims] 1. A repeater for relaying a signal received from a communication bus and sending the signal to the communication bus, when the received data received from the communication bus changes a predetermined number of times or more within a predetermined time , normal communication data is detected. When
Data detecting means for identifying and turning on the data detection signal, and turning it off otherwise, starting counting when the data detection signal is turned on, resetting when the data detection signal is turned off, and normal communication De
The counter that measures the time the data continues, the comparison means that compares the count immediately before the counter is reset with a predetermined value, and the count just before the counter is reset as a result of the comparison by the comparison means. Is greater than a predetermined value, a determination signal indicating that the received data is valid is output, and when less than the predetermined value, a determination signal that outputs a determination signal indicating that the received data is invalid. And a repeater. 2. The repeater according to claim 1, wherein the predetermined value is a minimum communication frame length.