JPH0124383B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a loop data transmission system in which a plurality of data transmission devices are connected in a cascade through a single signal transmission path and connected in a loop as a whole. Regarding.

More specifically, in a loop data transmission system, one transmission device in the loop has a reference frequency, and other transmission devices transmit and receive data by synchronizing with this frequency. Fault detection in transmission equipment that does not have a reference frequency in a loop data transmission system of the type that uses
and a control method for a loop data transmission system that uses a common bus to ensure that a transmission device having a reference frequency is informed of the condition when an out-of-synchronization is detected so that it can enter diagnostic operation. It is.

Fig. 1 shows a general configuration example of a transmission device (hereinafter referred to as station) system connected in a loop, Fig. 2 shows the receiving circuit of these stations, and Fig. 3 shows the receiving circuit. Phase-locked loop (hereinafter abbreviated as PLL) used for
This shows the characteristics of the voltage controlled oscillator in

In FIG. 1, stations 1-4 are connected in a loop by transmission lines 50-53. The station 1 has an oscillation circuit 8 that serves as a reference frequency for transmission data within the loop system, and a control unit 1
The transmission data from 1 is modulated by the modulation circuit 9,
The transmission circuit 10 transmits the signal to the station 2 via the transmission line 50. Station 2 regenerates a reception clock from the reception signal from the transmission path and demodulates data.

Further, the transmit data is modulated by a clock synchronized with the receive clock, and transmitted to the next stage station 3 via the transmission path 51. Station 3 similarly regenerates the reception clock and transmits the transmission line 52.
is transmitted to station 4 via. Similarly, station 4 is connected to station 1 via transmission line 53.
The synchronization circuit 6 reproduces a reception clock from the signal received by the reception circuit 5, and the demodulation circuit 7 demodulates the reception data and inputs it to the control section 11.
The control unit 11 performs the above-described transmission operation while buffering the received data with the oscillation circuit 8.

The internal blocks of stations 2-4 will be explained with reference to the diagram shown in station 3.

The reception signal is received by the reception circuit 12, the reception clock is regenerated by the synchronization circuit 13, and the reception clock is regenerated by the demodulation circuit 1.
4 demodulates the data and inputs it to the control section 17.
Transmission data synchronized with the reception clock and the transmission clock are modulated by the modulation circuit 15 and sent to the transmission circuit 1.
6 is input.

The difference between stations 2-4 and station 1 is whether the sending clock is a clock synchronized with the receiving clock or an independent clock.

FIG. 2 shows an example in which a phase-locked loop (hereinafter abbreviated as PLL) is used as the receiving side circuit of stations 1 to 4.

The signal received by the receiving circuit 18 via the transmission line 54 is sent to the timing extraction circuit 19 and the demodulation circuit 2.
6 is input. The timing extracted clock information is connected to the phase comparator 21 of the PLL 20. Phase comparator 2 as in the general PLL configuration
The output of 1 passes through a low-pass filter formed by an amplifier 22 and a capacitor 23, and is output to a voltage controlled oscillator 2.
4 is input. The oscillation output according to the input control voltage of the voltage controlled oscillator 24 passes through the counter 25,
A feedback loop is formed which is fed back to the phase comparator 21, and the reception clock 2a synchronized with the reception signal is regenerated. The output of the counter 25 is input to the demodulation circuit 26 and demodulated received data 2b
create.

In addition, the input voltage level of the voltage controlled oscillator 24 is
A synchronization pull-in signal 2c is obtained by the monitoring detection circuit 27. The characteristics of the input control voltage and output oscillation frequency of this voltage controlled oscillator 24 are shown in FIG.

The above is an example of a configuration of a loop type transmission system in which a group of stations connected in a loop has one reference frequency, and other stations are sequentially synchronized with this reference frequency.

Now, the operation of the loop type system when the loop type transmission line is disconnected and the signal is lost, or when a certain station breaks down and synchronization pull-in and transmission cannot be performed normally will be described.

Because they are connected in a loop, stations downstream of the station where these problems occur will no longer be able to synchronize because they will no longer be receiving regular reception signals, and the PLL will operate at a free-run frequency. That is, the operating point 3a in FIG. 3 shifts to the operating point 3b.

This information is sequentially transmitted to the next station, and it is necessary for the station in the loop to convey the malfunction status to the station that has the only reference frequency, and to display some kind of display and perform diagnostic operations. The problem is whether the status can be reliably communicated to the recipient.

If we consider the case where a station (2 to 4 in Figure 1) that reproduces data from a received signal simply operates at a free-run frequency, the characteristics of the voltage controlled oscillator shown in Figure 3 will allow it to operate in a free-run state. It cannot be passed on to the next level with certainty. That is, since the stations in the loop are placed under different environments, there are naturally differences in ambient temperature and power supply voltage. As shown in Figure 3, the station free run frequency F ₀ (control input voltage
The point where V _io is 0V) corresponds to the control voltage of 1.5V for a station at a temperature of 70°C, and since the control voltage is not 0V, it may not be considered a free run state.

FIG. 4 shows an explanatory diagram of the operation mode, which corresponds to FIG. 1. If the signal is cut off at 4x, blocks 4a, 4b, and 4c can detect out-of-synchronization, but block 4d cannot, and therefore cannot proceed to the diagnostic function.

To solve these problems, it would be good if the range of pull-in frequency of the voltage controlled oscillator in the PLL could be widened, but when the oscillation frequency exceeds around 10MHz, it is necessary to use a small capacitance and a variable capacitor in the voltage controlled oscillator. Due to the characteristics of the oscillator, such as the use of a crystal oscillator as a stable capacitor, the width is as narrow as the example shown in Figure 3.

In addition, it is possible to simply detect a received signal disconnection state, stop the transmission signal to the next stage, transmit it sequentially, and transmit it to a data transmission device having a reference frequency, as disclosed in JP-A-52.
It is known from the publication No.-95104. This method has the following problems. The data transmission device with the reference frequency transmits a signal to convey clock information in order to resume next time, but other dependent data transmission devices receive the received signal regardless of the completion of synchronization pull-in. However, since the synchronization pull-in state has not yet been achieved, even if normal data transmission is started, the data will be transmitted incorrectly. In order to avoid this, it is necessary to continue transmitting a signal for transmitting clock information for a sufficient period of time for all dependent stations to synchronize, and then to start normal data transmission operations. For this reason, regardless of the number of devices actually connected, it is necessary to wait for the start of normal data transmission for a period of time commensurate with the maximum number of connected devices as per the product specifications, resulting in a slow recovery time in the event of a loop down. It was hot. For example, assuming that the synchronization pull-in time is 200 μs per transmission device, and the specification for the maximum number of data transmission devices connected to the loop is 255,
The time to wait for the start of transmission is simplified for the sake of explanation, but it is approximately 200 μs x 255 units ≒ 50 ms or more, allowing for a margin of approx.
It will be 100ms. Considering the case where this loop type data transmission device is actually applied to a system with 10 devices connected, 200 μs x 10 devices = 2 ms degree, and even though it is synchronized, it will wait 100 ms, which is due to relay bypass. This poses a problem, such as the recovery time after a disturbance or when the power of the transmission device is cut off using the loop-back method that constitutes a detour becomes long.

The present invention was invented in view of the above points,
The purpose of this is to reliably notify transmission line disconnections and transmission device failures such as during relay bypass operation to the transmission device with the reference frequency, display the status of the loop transmission system, and perform failure diagnosis.
An object of the present invention is to provide a control method for a loop type data transmission system that can speed up data transmission restart and speed up the recovery time when a loop is down such as during a relay bypass operation.

A feature of the present invention is that each data transmission device for synchronization is provided with a receiving signal disconnection detecting means, a means for detecting a state in which synchronization is not pulled in, and a transmitting signal stopping means for stopping the transmission of the transmitting signal, When it detects that the received signal is disconnected or synchronization is not being pulled in, the transmission signal to the next stage data transmission device is stopped and the signal is transmitted to the next stage data transmission device only after the reception signal is detected and synchronization is detected. This means that the transmission signal is sent out. According to this, in the event of a transmission line disconnection or a failure of the transmission equipment,
Immediately, the next-stage data transmission device can reliably detect the same state, and thereafter, the downstream data transmission devices can sequentially repeat this process and notify the data transmission device having the reference frequency. Also,
When restarting, each data transmission device is designed to send out a transmission signal upon detection of a received signal and synchronization pull-in, so the transmission signal to the next stage is stopped at least until synchronization pull-in is detected. Therefore, when the received signal returns, the data transmission device having the reference frequency can recognize that the slave data transmission device connected in the loop is in the synchronous pull-in state, and the data transmission device having the reference frequency can recognize that the subordinate data transmission device connected in the loop is in the synchronous pull-in state. Data transmission can be resumed within a time commensurate with the actual number of connected devices without waiting.

FIG. 5 shows a configuration diagram of an embodiment of the present invention. Fifth
The figure shows an embodiment of a station that regenerates a reception clock from a reception signal and transmits it to the next stage using a transmission clock synchronized with this.

It is input to the receiving circuit 18 via the transmission line 54 and the output is sent to the timing extraction circuit 19 and the demodulation circuit 26.
is input to. Furthermore, it is also input to a detection circuit 31 that monitors the presence or absence of a received signal.

The output of the timing extraction circuit 19 is input to the PLL 20, and the outputs of the PLL 20 and the demodulation circuit 26 are input to the control section 29 as the reception clock and reception data, as in the conventional case.

The transmission data and clock from the control section 29 are input to the modulation circuit 28, and the transmission circuit 30 transmits the transmission data to the transmission line 5.
5 to the next station. Here, when the detection circuit 31 detects that there is no received signal, and when the detection circuit 27 detects an out-of-synchronization, a logical sum is taken at the gate 32, and the result is input to the modulation circuit 28. The transmission signal to the transmission path 55 is stopped by the transmission signal suppressing means 60.

As shown in the operational block diagram of FIG.
On the receiving side of all the stations 6b, 6c, and 6d, it is possible to detect signal loss and detect out of synchronization. This ensures that this status is transmitted to the station that has the reference frequency, and the station starts diagnostic operation.

Various methods are known for diagnostic operation, such as issuing a command to bypass the downstream stations one by one from the loop, or using another loop to loop back.
Since it is not directly related to the present invention, its explanation will be omitted here.

As described above, according to the present invention, abnormal conditions such as transmission line breakage and station synchronization loss can be reliably transmitted through one common transmission line bus in a loop transmission system. , system fault display and fault diagnosis can be performed automatically.
This speeds up the recovery time when the system goes down and improves system availability.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a configuration of a general loop data transmission system, Fig. 2 is a conventional block diagram of a receiving section that regenerates a clock from received data, and Fig. 3 is a block diagram of a conventional example of a receiving section used in the receiving section. A diagram showing a general characteristic example of the control input voltage and output oscillation frequency of a voltage controlled oscillator, FIG. 4 is an explanatory diagram of the operation when the transmission line is disconnected in the conventional example, and FIG. 5 is an example of an embodiment of the present invention. The block diagram shown in FIG. 6 is an explanatory diagram of the operation when the transmission line is disconnected in the present invention. 27... Out-of-synchronization detection means, 31... Reception signal diagnosis detection circuit, 60... Transmission signal suppression means.

Claims (1)

[Claims] 1 Multiple data transmission devices are connected in cascade through one signal transmission path, and as a whole,
In a loop data transmission system connected in a loop, one transmission device in the loop has a reference frequency, and other transmission devices transmit and receive data by synchronizing with this frequency. , each data transmission device is equipped with a receiving signal disconnection detecting means, a means for detecting a state in which synchronization is not pulled in, and a transmitting signal stopping means for stopping sending out a transmitting signal, When it detects that there is no synchronization, it stops sending the transmission signal to the next stage data transmission device, and sends the transmission signal to the next stage data transmission device only after detecting the received signal and synchronization pull-in. A control method for a loop data transmission system characterized by the following.