JPH06205022A - Signal transmission system - Google Patents

Abstract

PURPOSE:To provide a signal transmission system in which the delay permission value of data from a terminal equipment to a terminal equipment can be increased, and a transmissible distance can be extended. CONSTITUTION:A time after the lapse of the pulse width T of a start bit signal S1 (Ts) from the rising time T0 of the start bit signal S1 is used as a reference time, the time after the lapse of one bit time from the reference time is used as the time (first sampling point) when the first competition detecting operation is executed, and the time after the lapse of each one bit time since then is used as the sampling point. Therefore, when the delay of a signal transmitted by a terminal equipment B against the signal transmitted by a terminal equipment A is less than 1/2 bit time, the sampling point can be always set in a time zone where the time zone where the signal transmitted by the terminal equipment A can be a high level signal and the time area where the signal transmitted by the terminal equipment B can be the high level signal are overlapped by the terminal equipment A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to contention detection (CSM), which is one of channel access methods for connecting a plurality of terminals to one transmission medium and performing data communication by time division multiplexing.
A / CD) signal transmission system.

[0002]

2. Description of the Related Art Conventionally, in this type of signal transmission system, usually, each terminal device checks whether or not there is data on the transmission medium, and after confirming that there is no data on the transmission medium. ,
It is adapted to send signals to a transmission medium.

On the other hand, when a plurality of terminals transmit data to one transmission medium almost simultaneously, the plurality of data collide with each other on the transmission medium. In this case, contention detection is performed, and only the data that survives this contention detection is transmitted on the transmission medium.

FIG. 5 shows how the competition is detected. Figure 5
As shown in, the data transmission timings of the plurality of terminal devices A, B, C, D are substantially synchronized, and the plurality of terminal devices transmit data to the transmission medium substantially at the same time. The first data that survives this conflict detection is, as shown in FIG.
The data transmitted by the other terminals B, C, D have lost the competition, and the terminals B, C, D have stopped data transmission. Here, the contention-defeated data does not affect the contention-winning data sent to the transmission medium. In addition, the second data that has survived the competition detection is the data transmitted by the terminal device C, and the data transmitted by the other terminal devices A, B, D lose the competition, and the terminal devices A, B, D has stopped sending data.

FIG. 6 shows a communication system including the terminals A, B, ... D and a transmission medium. As shown in FIG. 6, a transmission / reception circuit and a transmission / reception control circuit are connected to each terminal. The transmission / reception control circuit detects the competition of the data, determines whether or not to stop the data transmission, synchronizes the data transmission timing of each terminal device, and transmits the data between the terminal device and the transmission / reception circuit. Hand over.

Further, the transmission / reception circuit serves as an interface between the transmission / reception control circuit and a transmission medium.

In the data output from the transmitting / receiving circuit, one byte is one signal group, and one signal group includes a start bit signal, a parity bit signal, and a stop bit signal. The waveform of the signal group has a duty ratio of 50% and is a binary signal that includes a positive pulse signal and does not include a negative pulse signal.
(RZ signal).

When the duty ratio is 50%, the waveforms of the above signal groups are AMI (alternate mark inversion) codes in which positive pulses and negative pulses alternate, as shown in FIG. May be

When a high level signal of data transmitted from one terminal unit and a low level signal of data transmitted from the other terminal unit collide on the transmission medium, a high level signal is generated. Has priority, and low level signals are canceled.

The transmission / reception control circuit, as shown in FIG. 7, has a sampling point at every 1 bit time.
It is designed to monitor the data on the transmission medium.
When the transmission / reception control circuit determines that the data transmitted by the terminal device to which the transmission / reception control circuit is connected and the data received from the transmission medium by the terminal device match, the data To continue sending,
It controls the terminal and the transmission / reception circuit. On the other hand, when the transmission / reception circuit determines that the data transmitted by the terminal device to which the transmission / reception control circuit is connected does not match the data received from the transmission medium by the terminal device, the transmission / reception circuit transmits the data. The terminal device and the transmission / reception circuit are controlled so as to stop.

Therefore, as shown in FIG. 7, in the transmission / reception control circuit of the terminal A, the data of the terminal A (low level signal) is the data of the terminal B at the second sampling point (second bit). Losing contention with the (high level signal), the terminal device A stops the data transmission from the third bit onward. On the other hand, the terminal device B continues to transmit data.

It should be noted that the first two cases are the competition judgments for continuing and stopping the data transmission based on the above-mentioned data matching and non-matching.
The data sent on the transmission medium will not be disturbed if it is always determined by bytes.

By the way, in the above signal transmission system, as shown in FIG. 7, the first sampling point is set at the time when a quarter bit time elapses from the rise of the start bit signal on the transmission medium. .

Therefore, from the time when the terminal A transmits the signal, when the signal reaches the terminal B, the terminal B which receives the signal transmits the signal, and when the signal reaches the terminal A. When the transmission distance between the terminal A and the terminal B is long such that the time until (the propagation delay time) exceeds 1/4 bit time, the terminal B at the position of the terminal A The waveform of the transmission data is 2 as shown by the dashed line in FIG.
It is also low level at the sampling point of the second time. Then, in this case, at each sampling point, the waveform of the transmission data of the terminal device B becomes low level, so that the terminal device A cannot detect the competition.

As described above, in the signal detection method, if the propagation delay time exceeds 1/4 bit time, conflict detection cannot be performed. Therefore, the propagation delay time should be less than 1/4 bit time. However, there is a problem that the transmission distance must be restricted to be short.

As another signal detection method, as shown in FIG. 8, the terminal A uses the width T of the start bit signal.
A method in which 20 is measured and a time point that is 1/4 bit time before the falling time point of this start bit signal is the reference time of the sampling point, and 1 bit time after this reference time is the first sampling point. There is. In this method, sampling is performed every 1 bit time from the first sampling point, the width of the start bit signal is measured again with the next start bit signal, and the width of the start bit signal is measured 4 times after the falling point of the start bit signal. The point one minute before the bit time is used as the reference point of the sampling point.

However, in this signal detection system, as shown in FIG. 8, the data transmitted by the terminal A, the data transmitted by the terminal B, and the data transmitted by the terminal C compete with each other, and The data sent by the terminal device C is the data of the terminal device A.
When the data sent by the terminal B and the data sent by the terminal B are delayed by a quarter bit time or more, the time point before the falling time of the start bit signal is a quarter bit time before the reference time. The data transmitted by the terminal A and the terminal B at each sampling point that is the time
The data sent by is always low. For this reason,
There is a problem that the terminal A cannot detect that it is in conflict with the terminal B.

[0018]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a signal transmission system capable of increasing a delay tolerance of data from a terminal to a terminal and extending a transmittable distance. To provide.

[0019]

In order to achieve the above object, the signal transmission system of the present invention is such that when a high level signal and a low level signal collide, the low level signal is canceled while the high level signal is canceled. The pulse signals from the plurality of terminals are output to the transmission medium adapted to transmit the level signal, and the above terminal determines whether the signal transmitted by itself and the signal received from the transmission medium match. Judge whether
If you determine that the signal you sent and the signal received from the transmission medium match, you continue to send the signal, but the signal you sent does not match the signal received from the transmission medium. When the determination is made, in the signal transmission method in which the competition detection operation of stopping the signal transmission is executed only for a predetermined period at every 1 bit time which is the minimum period of the pulse signal, The time when only one half of the pulse width of the start bit signal has elapsed from the rising time of the start bit signal, which is the first pulse signal of the pulse signal, is set as the reference time, and n bits time later (n: It is characterized in that the natural number) is the time when the first conflict detection operation is performed.

[0020]

According to the above signal transmission system, the time when a half of the pulse width of the start bit signal has elapsed from the rising time of the start bit signal is set as the reference time,
The time when the first conflict detection operation is performed is n bits time (n is a natural number) from this reference time. Therefore, when the high-level signal transmitted by one terminal and the high-level signal transmitted by the other terminal form the start bit signal, two high-level signals of the two terminals are generated. The middle of the time domain where the signals are overlapped is set as the reference time of the sampling point where the conflict detection operation is performed. Then, the conflict detection is performed every 1 bit time after n bits time from the reference time.

That is, the delay of the signal transmitted by the other terminal with respect to the signal transmitted by one terminal is approximately one half.
If it is less than the bit time, one terminal may have a high-level signal in the time domain in which the signal transmitted by one terminal may be a high-level signal, and the signal transmitted by the other terminal may be a high-level signal. It is possible to set each sampling point in a time domain in which the time domain in which there is a possibility overlaps, and it is possible to reliably execute the conflict detection. Therefore, according to the present invention, the propagation delay allowable time can be extended to less than half the bit time, which is almost twice as long as the conventional example, and the transmission distance can be extended.

Further, even when the high level signals transmitted from three or more terminals form the start bit signal,
If the time difference between the two high-level signals with the most time lag is less than about a half bit time, the signal transmitted by each of the three terminals may have a high level. You will set sampling points in the area,
Conflict detection can be executed reliably. Therefore, according to the present invention, the propagation delay allowable time can be extended to less than half the bit time, which is almost twice as long as the conventional example, and the transmission distance can be extended.

[0023]

The present invention will be described in detail below with reference to the embodiments shown in the drawings.

An embodiment of the signal transmission system of the present invention will be described with reference to FIG. 1A shows a signal waveform transmitted by the terminal A to the transmission medium, and FIG. 1B shows a signal waveform transmitted by the terminal B to the transmission medium and received by the terminal A. The signal waveform on the transmission medium received by the terminal A is shown in (C). As shown in FIG. 1, the minimum period of the signal waveform is 1 bit time.

As shown in FIG. 1, when a high level signal and a low level signal collide with each other on the transmission medium, the low level signal is canceled and the high level signal is transmitted. .

Next, the competition detection circuit provided in each terminal in the above embodiment will be described with reference to the block diagram shown in FIG. In FIG. 3, reference numeral 31 is an edge detection circuit that monitors the signal on the transmission medium and detects the rising edge and the falling edge of the start bit signal. 33
Is a counter that starts counting at the rising edge of the received start bit signal and stops counting at the falling edge of the start bit signal. The counter 33 counts the clock pulses of the clock 36 using the clock 36 having a cycle sufficiently faster than the signal transmission speed in the transmission medium, and outputs half of this count value to the comparator 34. Start bit signal pulse width T =
Since (count value) × (clock cycle), (count value) / 2 corresponds to a time T _S that is ½ of the pulse width T of the start bit signal. Then, as described above, if a clock that is sufficiently faster than the signal transmission rate is used, the error when evaluating the time Ts and the error when calculating half of the count value can be made sufficiently small.

The counter 35 starts counting 1 bit after the rise of the start bit signal and sends the counted value to the comparator 34. This counter 35
Converts the time into a count value.

The comparator 34 counts the count value representing the time T / 2 output from the counter 33 and the counter 3
When the count value of the counter 35 and the count value of the counter 35 match, the match signal is output. That is, the comparator 34 is
A coincidence signal is output at the time when (time T / 2) + (1 bit time) has elapsed from the rising time of the start bit signal. When the sample timing signal generator 32 receives the coincidence signal from the comparator 34, the sample timing signal generator 32 uses this coincidence signal as a trigger until the next start bit signal reaches 1
A sample timing signal is output every bit time.

The clock 36 is a clock for the counter 33 and the counter 35, and has a clock cycle sufficiently faster than the signal transmission speed.

The counter 33, the counter 35, the comparator 34, and the sample timing signal generator 32 are reset by the rising time of the next start bit signal.

The comparison circuit 37 compares the received signal with the transmitted signal, and when the received signal and the transmitted signal do not match, outputs a transmission stop signal for stopping the transmission to the gate circuit 38. When the gate circuit 38 receives the transmission stop signal from the comparison circuit 37, it stops transmitting the transmission signal. The comparator 37 and the gate circuit 38 are reset by the next rising edge of the start bit signal.

The RZ signal conversion section 40 includes the gate circuit 3
The transmission signal received via 8 is converted into an RZ signal which is a binary signal composed of a high level signal and a low level signal.

The decision circuit 39 decides the received signal at the time when the sample timing signal output from the sample timing signal generator 32 is received.

Next, in this embodiment, the operation in which the terminal A detects the conflict will be described below. First, the terminal device A
The start bit signal which is the first pulse signal of the group of pulse signals transmitted by the transmission medium is received, and the pulse width T of the start bit signal is measured.

Next, the terminal device A performs the conflict detection operation at time T ₁ when a time T _{S that} is one half of the pulse width T of the start bit signal elapses from the rising time T ₀ of the start bit signal. Set the reference time to determine the sampling point, which is the time.

Then, the terminal A sets the sampling point T ₂ as the first sampling point 1 bit time after the reference time T ₁ of the sampling point, and detects the competition every 1 bit time from the first sampling point T _2. To do. That is, the terminal device A determines whether or not the signal transmitted by itself and the signal received from the transmission medium coincide with each other at every 1 bit time from the first sampling point T ₂ and then transmits by itself. If it determines that the signal matches the signal received from the transmission medium, it continues to transmit the signal, while if it determines that the signal transmitted by itself does not match the signal received from the transmission medium. Performs a conflict detection operation to stop signal transmission. The terminal device A executes the contention detection operation for a 2-byte period.

In the above embodiment, at the first sampling point T ₂ , in the terminal A, the signal transmitted by itself (high level signal) matches the signal received from the transmission medium (high level signal). Then, the signal transmission is continued. On the other hand, the terminal device B determines that the signal transmitted by itself (low level signal) does not match the signal received from the transmission medium (high level signal), and stops transmitting the signal.

As described above, according to the above embodiment, the terminal A uses the time T _{1 in} the middle of the start bit signal as the reference time of the sampling point, so that the high level signal of the terminal A and the terminal B are set. That is, the middle of the period in which the high-level signal of 1 is overlapped with is the reference time. Therefore, if the delay of the signal transmitted by the terminal B with respect to the signal transmitted by the terminal A is less than a half bit time, the signal transmitted by the terminal A may be a high level signal. Each sampling point can be set in a time domain in which the time domain in which the signal transmitted from the terminal B is likely to be a high-level signal overlaps with the time domain in which there is a possibility .

Therefore, according to the above embodiment, the allowable signal delay time can be doubled as compared with the conventional example in which the signal delay time is limited to less than 1/4 bit time, and the transmission distance is increased. Can be extended.

The delay time of the signal is 2 times the transmission time d required for the signal to be transmitted from one terminal to the other terminal.
Double round trip transmission time 2d, transmission delay time Td from when a signal arrives from the one terminal to the other terminal until the other terminal transmits a signal, and error in signal transmission rate And the transmission time error α due to That is, if the delay time of the above signal is TE, TE
= Td + 2d + α.

Therefore, according to the above embodiment, 1/2
If bit time> TE, the conflict detection can be accurately executed. That is, the transmission time d <(1/2 bit time-Td-
It may be α) / 2.

For example, 1 bit time = 104 μsec, T
d = 13 μsec, α = 5.4 μsec, and the propagation velocity is 6.5.
Transmission time d <(52-13-5.
4) /2=16.8 μsec. Therefore, the maximum transmission distance is 16.8 / 6.5 = 2.58 km. On the other hand, in the conventional example, if the 1/4 bit time> TE is not satisfied, the contention detection cannot be accurately performed, so that the transmission time d <(2
6−13−5.4) /2=3.8 μsec, and the maximum transmission distance becomes 3.8 / 6.5 = 0.58 km. As described above, according to the above-described embodiment, the data transmission distance can be significantly extended as compared with the conventional example.
In the above embodiment, the reference time of the sampling point is updated for each start bit signal. because,
The sampling point for each bit based on the reference time set in the middle of the first start bit signal S1 shown in FIG. 1 is generally the next start bit signal S2 (see FIG. 2).
This is because it is not located in the middle of (), and therefore, if the reference time of the sampling point is not updated, conflict detection becomes uncertain.

In the above embodiment, each terminal may be provided with the competition detection circuit shown in FIG. 4 instead of the competition detection circuit shown in FIG. The edge detection circuit 43 of the competition detection circuit shown in FIG. 4 receives a start bit signal from the transmission medium via the transmission / reception circuit 42, outputs a rising signal at the rising time of the start bit signal, and outputs the start bit signal. The falling signal is output at the signal falling time.

The counter 44 starts counting when it receives a rising signal from the edge detection circuit 43 and stops counting when it receives a falling signal from the edge detection circuit 43. That is, the counter 44 measures the pulse width T of the start bit signal and converts the pulse width T into a count value. further,
The counter 44 calculates a count value corresponding to one half of the pulse width T and outputs this count value to the microcomputer 41.

From the rising time of the start bit signal, the microcomputer 41 calculates (1 bit time + T
/ 2) The time after the time is set as the first sampling point. At this first sampling point,
The signal of the second bit next to the start bit signal becomes fixed. Then, the microcomputer 41
Performs the conflict detection every 1 bit time after the first sampling point. Then, the microcomputer 41, even in the next start bit signal,
Similar to the above, the sample timing is determined and the competition is detected.

[0046]

As is apparent from the above, in the signal transmission system of the present invention, the time when approximately one half of the pulse width of the start bit signal has elapsed from the rising time of the start bit signal is set as the reference time, and The time at which the first conflict detection operation is performed is n bits after the reference time (n is a natural number).

Therefore, if the delay of the signal transmitted by the other terminal with respect to the signal transmitted by the one terminal is less than approximately one-half bit time, one terminal will always Sampling points should be set in the time domain where the signal to be transmitted may be a high level signal and the time domain to be transmitted by the other terminal may be a high level signal. Therefore, the conflict detection can be surely executed. Therefore, according to the present invention, the propagation delay allowable time can be extended to less than half the bit time, which is almost twice as long as the conventional example, and the transmission distance can be extended.

In addition, even when the high level signals transmitted by three or more terminals form the start bit signal,
If the time difference between the two highest-level signals with the most time lag is less than one-half bit time, that is, if the pulse width of the start bit signal is less than one bit time, then each of the three terminals Since the sampling point is set in the time domain in which the signal transmitted by the container may be at a high level, the conflict detection can be surely executed. Therefore, according to the present invention, even when contention detection of signals transmitted by three or more terminal devices is performed, the allowable propagation delay time is extended to less than half the bit time, which is almost twice as long as the conventional example. Therefore, the transmission distance can be extended.

[Brief description of drawings]

FIG. 1 is a diagram showing each signal waveform of an embodiment of a signal transmission system of the present invention.

FIG. 2 is a signal waveform diagram for explaining updating of the reference time of the sampling point in the above embodiment.

FIG. 3 is a block diagram showing an example of a conflict detection circuit included in the terminal device of the above embodiment.

FIG. 4 is a block diagram showing another example of a conflict detection circuit included in the terminal device of the above embodiment.

FIG. 5 is a conceptual diagram of competition detection.

FIG. 6 is a block diagram showing a communication system that performs contention detection.

FIG. 7 is a diagram showing each signal waveform in a conventional signal transmission system.

FIG. 8 is a diagram showing each signal waveform in another conventional signal transmission system.

FIG. 9 is a waveform diagram showing an AMI code.

[Explanation of symbols]

T ... pulse width of start bit signal, S1, S2 ... start bit signal.

Claims (1)

[Claims] 1. When a high level signal and a low level signal collide with each other, the low level signal is canceled and the high level signal is transmitted from a plurality of terminals to a transmission medium. The pulse signal of is output, and the terminal determines whether the signal transmitted by itself matches the signal received from the transmission medium and determines whether the signal transmitted by itself and the signal received from the transmission medium If it determines that the two signals match, it continues to transmit the signal, while if it determines that the signal that it has transmitted does not match the signal received from the transmission medium, it stops transmitting the signal. In the signal transmission method in which the operation is executed for a predetermined period at every 1-bit time which is the minimum period of the pulse signal, the start pulse which is the first pulse signal of the group of pulse signals transmitted by the transmission medium is The time at which the pulse width of the start bit signal has risen by approximately half of the pulse width of the start bit signal is set as the reference time, and the first conflict detection operation is performed after n bit time (n is a natural number) from this reference time. A signal transmission method characterized in that it is time to perform.