JPS6349944B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a loop data transmission system in which data transmission devices are connected in a ring and data is transmitted between arbitrary data transmission devices.

Generally, in the loop data transmission method, as shown in Figure 1, data transmission devices ST1 to ST4 are connected in a ring on a transmission path, and these data transmission devices ST1
Terminals TM1 to TM6 are connected to terminals TM1 to TM4, respectively. Data transmission from the data transmission device of the transmitting station to the data transmission device of the receiving station is performed between each station using the data format shown in FIG. At the data transmitting station, the frame synchronization word F is inserted into the time slot that is permitted for transmission.
SYNC, source address SA, destination address
Along with RA, the information word DATA is allocated and sent on the transmission path. The data receiving station indicated by the destination address RA receives the information word DATA and sends out the time slot as an empty time slot. In such a loop data transmission method, if both the destination address RA and the source address SA become addresses that do not exist on the loop due to a disturbance in the transmission line, the time slot will be permanently routed on the loop. In order to avoid monopolization, one of the data transmission devices has a time slot monitoring function that monitors the destination and source addresses of the time slot that transmits the loop, and removes the time slot that indicates an address that is not registered in the loop. If detected, the time slot is also immediately sent out as an empty time slot. This requires a storage circuit and a control circuit for storing addresses on the loop, which has the disadvantage of increasing the circuit scale. Furthermore, there is a drawback that it is not possible to cope with the disappearance/occurrence of addresses due to removal/insertion of a device from a transmission path by bypass control performed at the time of failure/recovery of a data transmission device.

SUMMARY OF THE INVENTION An object of the present invention is to provide a loop data transmission system that eliminates the above-mentioned drawbacks.

The loop data transmission system of the present invention is a loop data transmission system in which data transmission devices are connected in a loop to transmit and receive data between each other, in which at least one of the data transmission devices is connected to an arbitrary time slot, and the other data transmission devices are connected in a loop. A flag indicating that the data transmission device is permitted to receive data in the time slot and prohibited to transmit the data is sent to the data transmission device, and after the time slot has gone around the loop-shaped transmission path, the data is transmitted to the empty time slot. It is characterized in that it is determined whether the

A feature of the present invention is that in a data transmission device that has become a monitoring station, a transmission prohibition flag is added to the time slot to be monitored and the data is transmitted, so that the data transmission device can be used for new data transmission to other data transmission devices. By prohibiting data transmission and enabling data reception for frames that have already been transmitted, the time slot becomes an empty time slot after going around the loop once without causing data loss. It is in.

Next, embodiments of the present invention will be described in detail using the drawings.

As shown in Figure 1, data transmission equipment ST1-4
are connected in a ring. Data transmission device ST1
serves as a system control station and has a timing signal generation function that regulates the time slots shown in FIG. 3, controlling so that there are temporally continuous time slots at any point on the transmission path. The other devices ST2 to ST4 are synchronized with this and constantly monitor the time slot. As shown in Figure 3, the data format of the transmission signal includes a frame synchronization word FSYNC for frame synchronization, a flag bit FB indicating whether the time slot is used, and a transmission prohibition indicating whether transmission is prohibited. It consists of a flag bit SI, a source address SA indicating the address of the transmitting station, a destination address RA indicating the address of the data receiving station, and an information word DATA carrying the transmitted data.

Consider the case where data is transmitted and received using such a time slot. If a station receives a time slot where FB indicates unused and SI indicates transmittable and there is data to be transmitted, the FB of the frame is set to be in use, SA is changed to the own station address, RA is changed to the destination address, The data is placed on the following information word and transmitted. The data receiving station monitors the time slot sent from the upper station, and if FB indicates data presence, SA indicates the address of another station, and RA indicates the address of the own station, the data is received from the station indicated by SA. It determines that the data is for its own station and receives the data. The received frame is sent to the FB at the receiving station.
is sent to the lower station as having no data.

An example of the data transmission device shown in FIG. 1 is shown in FIG. A received signal a from an upper station is converted into a TTL level input signal b by a receiving interface circuit 1, and then input to a receiving buffer 12. A reception clock c synchronized with the input signal b is generated by the timing detection circuit 2. The input signal b is input to the frame synchronization circuit 13, and the frame synchronization signal d is input to the bit counter circuit 3, which counts the number of bits for one frame.
The required clock is created. A gate 6 compares the local station address outputted by the address generation circuit 5 and the SA of the input signal b, and if they match, the output of the flip-flop 8 is set to 1. Similarly, the own station address and RA are compared at the gate 7, and if they match, the output of the flip-flop 9 is set to 1. If the FB of the input signal b indicates the presence of data, the output of the flip-flop 10 is set to 1, and if the SI indicates that transmission is not possible, the output of the flip-flop 11 is set to 1. The operation mode shown below is determined using the above output signals.

(1) If FB has data and neither SA nor RA has its own station address, the output of gate 23 opens gate 30 via gate 29, and data e from reception buffer 12 is sent to gates 34, 35 and transmission interface circuit 36. and then sent to the lower station.

(2) If the FB has data and RA = own station address, the gate 31 is opened by the output of the gate 16, and the received data k is received, and the gate 33 is opened via the gate 22, and the FB of the time slot is marked as having no data. The selected time slot is transmitted to the lower station.

(3) If FB has data and SA = own station address, output from gate 20 passes through gate 22 to gate 3.
3 and set the FB of the time slot to have no data.

(4) If FB has no data and SI can be sent,
If there is a transmission request h, a transmission enable signal i is outputted through the gate 26 and the flip-flop 27, and at the same time the gate 28 is opened and the transmission data j is sent to the gate 3.
4, 35, and is transmitted to the lower station via the transmission interface circuit 36. If there is no transmission request h, the outputs of gates 25 and 24 open gate 30 via gate 29, and the time slot is directly sent to the lower station.

On the other hand, in the data transmission device serving as a time slot monitoring station, the setting switch circuit 19 outputs a monitoring station signal f (always "1") to control the monitoring operation. The monitoring timing g output from the monitoring timing generating circuit 18 passes through the gate 32 opened by the signal f, and disables the transmission of the SI of the sending frame. The monitoring timing signal g becomes "1" or "0" in frame units, and sets the frame to be monitored to "1". The distribution of “1” and “0” may be random. In the monitoring station, for time slots where the SI of the received signal that has gone through the loop cannot be transmitted, the output of the gate 21 is used to open the gate 33 via the gate 22 and transmit the signal to the time slot.
A time slot with no data on FB and transmission enabled on SI is sent to the lower station.

If the received signal that has gone around the loop is normal,
Although the FB indicates no data, the FB may indicate the presence of data at a time slot where SA and RA indicate an address that does not exist on the loop due to a data error or the like. In this case, by setting the FB to no data, control is performed so that no data is transmitted on the loop forever.

According to the present invention, since it is necessary to store and monitor addresses in the control for removing frames whose destinations are unknown from the loop, the present invention has the feature that even if an address changes, it can be monitored completely independently. Furthermore, it is possible to cope with the disappearance/occurrence of addresses due to the removal/insertion of a device from a transmission path by bypass control performed at the time of failure/recovery of a data transmission device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a general loop data transmission method, and FIG. 2 is an explanatory diagram showing a data format in the conventional loop data transmission method.
FIG. 3 is an explanatory diagram showing a data format in an embodiment of the invention, and FIG. 4 is a circuit diagram showing a data transmission device in an embodiment of the invention. ST1, ST2, ST3, ST4...Data transmission device, TM1, TM2, TM3, TM4, TM5,
TM6...Terminal device, F SYNC...Frame synchronization word, SA...Source address, RA...Destination address, DATA...Information word, FB...
Flag bit, SI...Send inhibition flag bit.

Claims (1)

[Claims] 1. In a loop data transmission system in which data transmission devices are connected in a loop to send and receive data between them, at least one of the data transmission devices acts as a monitoring station and sets a flag at a predetermined time slot of any frame. In a data transmission device other than the transmitter and the monitoring station, when the flag is set in the predetermined time slot, the data transmission device receives the frame but prohibits data transmission, and the frame transmits the data through the loop-shaped transmission path. A loop data transmission system characterized in that when the flag is set in the predetermined time slot of the frame received by the monitoring station after one round, the frame is determined to be an empty frame. .