JPS6367379B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data communication system, and more particularly to a data communication system in a system in which a plurality of devices perform data transmission using a common communication medium.

When a communication medium is shared by a plurality of devices, there may be conflicts in the use of the communication medium, such as transmission requests, between the devices.

Conventionally, a method disclosed in Japanese Patent Application Laid-Open No. 114804/1983 has been known as a method for resolving such conflicts. This method includes a conflict counting device that integrates transmission conflict signals and a random number generator that generates a random number signal, and the conflict count is weighted by random numbers, and the result is used as the retransmission timing. This method eliminates simultaneous retransmissions, that is, repeated conflicts.

A practical drawback of this method is that it does not take into account the frequency of use of the devices used. Operators of frequently used equipment feel particularly psychologically distressed by being kept waiting, and it is desirable that the data communication system take this into account.

SUMMARY OF THE INVENTION An object of the present invention is to provide a data communication system that eliminates the above-mentioned drawbacks of conventional data communication systems and allows retransmission timing to be set in accordance with the frequency of use of the device in use.

In order to achieve the above object, the data communication system of the present invention includes a plurality of utilization devices each including a communication medium and a transmitting circuit and a receiving circuit connected to the communication medium. The utilization device includes a conflict signal generating device provided between the transmitting circuit and the receiving circuit, a call counter device that counts the number of transmission blocks transmitted from the transmitting circuit when there is no conflict signal, and a call counter device that counts the number of transmission blocks transmitted from the transmitting circuit when there is no conflict signal. The present invention is characterized in that it is provided with a retransmission control device that retransmits the transmission earlier in a certain case as the count value of the call counter device is higher.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 is a schematic block diagram showing one embodiment of the present invention, and FIG. 2 is a block diagram showing its details.

The data transmission system shown in this embodiment consists of a utilization device 3 having a transmitting circuit 1 and a receiving circuit 2, and a collision circuit 4.
and are connected to a common transmission line 5.

In the transmission operation, data from the utilization device 3 is transferred to the shift register 14 through the output buffer 16.
The signal is temporarily stored in , and sent to the transmission line 5 through the phase encoder 12 and driver 11 .

In the receiving operation, the input signal from the transmission line 5 is inputted to the phase decoder 22 through the receiver 21, where data and clock are distinguished and the data is stored in the shift register 23.

The first data is compared with the own address in the address identification circuit 24, and if it is the own address, the subsequent data is sent to the utilization device 3 through the input buffer 25.
is input.

As described above, since the transmitting circuit 1 and the receiving circuit 2 are connected to the common transmission path 5, the transmitted/received signal comparison circuit 42 constantly compares its own transmitted signal with the signal on the transmission path. If there is no transmission from another usage device, the transmission signal and the reception signal match, but if transmission from another usage device is received, the transmission signal and the reception signal are determined to be mismatched by the transmission/reception signal comparison circuit. 42 is detected. This is called a "collision detection signal." This signal is input to the transmission control circuit 15, which stops its own transmission and waits for retransmission timing.

When the transmission is performed normally, the amount of transmitted data is incremented and stored in the call origination counter 47. When the collision detection signal is output as described above, the data stored in the call counter 47 is input to the retransmission counter 43. A retransmission clock 44 is provided to the retransmission counter 43, and the time until the retransmission counter 43 overflows becomes the retransmission wait timing. When the retransmission counter 43 overflows, the transmission control circuit 15 starts transmission again.

Since the call origination counter 47 is incremented as the amount of data transmitted from the own device 3 increases, this output shortens the time required for the retransmission counter 43 to overflow, that is, the waiting time. This indicates that in the event of a collision with another less frequently used device (transmitted data amount is small), data can be transmitted with priority over that device.

In order to prevent re-collision from occurring when the call counters 47 of a plurality of devices have exactly the same value, a random number counter 48 and circuits 45 and 46 that weight the output of the random number counter 48 and the output of the light emission counter 47 are provided. It is provided.

It is desirable to provide means such as a battery 50 so that the memory of the call counter 47 does not disappear even when the power to the device is turned off.

Incidentally, when it becomes necessary to intentionally set transmission priority rights to each user device, the calling counter of each user device can be set via the transmission path 5. For example, data with an identification code attached to the beginning is sent along the path of receiving circuit → utilization device → calling counter, and the above data is set in the calling counter. In this case, since the call counter may exceed a predetermined number of digits, it is better to interrupt the device 3 and issue a reset command to all the devices connected to the transmission line 5.

As described above, according to the present invention, the frequency of use of each device is taken into consideration when determining the priority in data retransmission after a collision occurs.
A data communication system that is extremely effective in practice can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the outline of the present invention, Figure 2 is a block diagram showing an overview of the present invention.
The figure is a block diagram showing one embodiment. 1: Transmission circuit, 2: Receiving circuit, 3: Utilization device,
4: Collision circuit, 5: Transmission line, 11: Driver, 1
5: Transmission control circuit, 21: Receiver, 4
2: Transmission/reception signal comparison circuit, 43: Retransmission counter,
47: Call counter.

Claims (1)

[Claims] 1. In a data communication system consisting of a plurality of utilization devices equipped with a communication medium and a transmission circuit and a reception circuit connected to the communication medium, the plurality of utilization devices are provided with a a conflicting signal generating device, which counts the number of transmission blocks transmitted from the transmitting circuit when there is no conflicting signal; and a retransmission control device for early retransmission timing.