JPH0720112B2 - 2-wire area information and communication network - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention is a two-wire regional information communication network (hereinafter, LAN (Local
Area Network). ), A LAN in which a plurality of small computers such as personal computers are connected by a normal telephone line, that is, a single two-wire cable.

[Prior art]

LAN is being constructed as a data communication network between small computers. A star LAN system developed by AT & T in the United States is known as a LAN using a two-wire cable called a telephone line or a pair cable. In FIG. 2, personal computers (personal computers) A, B, C, ... N as the small computer 1 are network hubs.
An example of a star LAN system radially connected to the unit NHU2 is shown, and the principle is shown in FIGS. 3, 4A and 4B. Communication cable 3 to connect each PC to NHU2
Is composed of four wires, a two-wire transmission cable S and a two-wire reception cable R. That is, the star LAN system requires a pair of two-wire cables for each small computer 1. The operation will be described. For example, when the personal computer A sends the information signal IA to the transmission cable S at the time t0 in FIG. 4A, the signal is transmitted through the bus lines L1 and L2, the NHU2 lines N1 and N2, and the bus lines N3 and N4 to the reception cables of all the personal computers. Added to R. Information signal IA
The receiving personal computer designated in the figure takes in the information signal IA in response to the designation. At the same time, the information signal IA is the personal computer A
Return to the receiving cable R of. The personal computer A confirms the normal transmission by detecting the coincidence of the sending signal and the return signal, and continues the sending, and finishes sending the information signal at time t1. After that, another personal computer, for example, personal computer B, is allowed to send the information signal after waiting the waiting time W necessary for preventing interference. That is, the star LAN system uses multiple access (Carrier Sense Mu
ltiple Access (CSMA) method. Referring to FIG. 4B, when the personal computer A is transmitting the information signal IA, the personal computer B transmits the information signal IB at a time (t1-Δt) before the end time t1 of the information signal IA for some reason.
, The personal computer A simultaneously receives its own return signal IA and the information signal IB from the personal computer B, so that its own transmission signal IA and its reception signal (IA + IB) become different. By detecting the difference, that is, inconsistency, detection of signal collision (Collision Detection, CD) becomes possible. In response to this detection, the personal computer A sends the collision signal CD and stops sending its own information signal IA. PC B
Shows its own information signal at time tc in response to receiving the collision signal CD.
Stop IB hitting. After confirming that there is no signal on the bus lines L1, L2, L3, L4 for an appropriate waiting time W, the personal computer A and the personal computer B retransmit the information signal in the same order as in the case of normal operation.

[Problems to be Solved by the Invention]

The star LAN system described above provides a CSMA / CD type LAN using an ordinary telephone cable.
There is still room for improvement in that one pair of 2-wire cables is used for each small computer and that an NHU is indispensable. FIG. 5 shows the configuration of a LAN system in which the communication cable of the small computer 1 is one 2-wire cable. If the communication cable 3 of each small-sized computer 1 is simply a two-wire cable, it is difficult to compare the sending signal and the return signal, and the signal collision cannot be detected. As a result of various experimental studies, the inventors of the present invention have detected a signal collision during transmission of an information signal even if the communication cable of each small computer is used as one two-wire cable if the signal collision is detected by using a directional bridge circuit. I noticed that I could do it. FIG. 1 shows the connection between the directional bridge circuit 10 and the LAN system, and FIG. 6 shows the principle of the directional bridge circuit 10. Referring to FIG. 6, the small computer 1 is connected to the load 11 by the communication cable 3 which is a two-wire cable. Here, the load 11 is the impedance seen from the output points P3, P4 of the directional bridge circuit on the LAN side, that is, the external circuit in FIG. One electric wire of the communication cable 3 has a connection point P1.
Is connected to the series resistor R1, and the other end of the series resistor R1 serves as one output point P3 of the directional bridge circuit 10. The other wire of the communication cable 3 has a series resistance at the connection point P2.
The other end of the series resistor R2 connected to R2 is the other output point P4 of the directional bridge circuit 10, and the load 11 is connected to both output points P3 and P3.
Connected between 4. A plow resistor R3 is connected between the coupling point P1 and the other output point P4, another plow resistor R4 is connected between the coupling point P2 and one output point P3, and two detection terminals DT Is the contact point P
5 and P6 touch the scraping resistors R3 and R4 respectively. The series resistors R1 and R2, the shunt resistors R3 and R4, and the contact terminal DT thus connected form the directional bridge circuit 10. In FIG. 6, the load 11 surrounded by the alternate long and short dash line is shown inside the directional bridge circuit 10 for the sake of convenience, but it goes without saying that the actual load 11 is outside the directional bridge circuit 10 as shown in FIG. Absent. When the load 11 is a passive circuit with a large impedance value, the resistance value and contact point of the series resistors R1 and R2 and the stacking resistors R3 and R4
By appropriately selecting the positions of P5 and P6, the voltage between the two detecting elements DT can be made zero regardless of the voltage fluctuation between the connecting points P1 and P2. For example, when the load 11 is an infinite resistance, r1 = (R1 + r2) is the condition for zero output at the detection terminal DT. Here, r1 is the resistance value between the coupling point P1 and the contact point P5, R1 is the resistance value of the series resistor R1, and r2 is the resistance value between the output point P3 and the contact point P6. If this zero output condition is satisfied, the output of the detection terminal DT is maintained at zero even if the voltage between the connection points P1 and P2 changes according to the value of the information signal. When the load 11 changes to an active circuit that generates a signal in this state, the current distribution in the directional bridge circuit 10 changes and an output is generated at the detection terminal DT. Therefore, the directional bridge circuit
10 can detect an incoming call during the transmission of an information signal by one 2-wire cable, that is, a signal collision can be detected. However, this directional bridge circuit 10 is always LAN
If it is connected to the system, the impedance of each small-sized computer 1 as seen from the system side is lowered, and it is difficult to ensure normal operation. Therefore, an object of the present invention is to provide a two-wire type intra-region information communication network which has a high input impedance of a small computer and can detect a signal collision.

[Means for Solving the Problems]

The configuration of the two-wire intra-region information communication network according to the present invention will be described with reference to the embodiments shown in FIGS. 1, 5, and 6. When connecting a plurality of small computers 1 to the two busbars L1 and L2 via a communication cable 3 consisting of a two-wire cable, the output terminals of each small computer 1 were connected in series to the two wires of the communication cable 3. Two series resistors R1 and R2, two plow resistors R3 and R4 selectively connected in a bridge shape to the both series resistors R1 and R2, and two plow resistors R3 and R4 contacting each other 2
A directional bridge circuit 10 having one detection terminal DT is connected. According to the present invention, the open / close switch SW1 is connected between the series resistors R1 and R2 and the knock resistors R3 and R4. The open / close switch SW1 at the output end of the small computer that is not transmitting is opened to separate the tapping resistors R3 and R4 from the series resistors R1 and R2, and the open / close switch SW1 at the output end of the small computer that is transmitting is closed. Then, the bridge connection is completed, and the occurrence of signal collision due to a signal other than the signal sent by the transmission is detected by the voltage change between the both detection terminals DT. Preferably, a two-pole changeover switch SW2 is provided for selectively connecting the two-wire communication cable 3 connected to the bus lines L1 and L2 to the small computer 1 and the pseudo circuit Z of the small computer.

[Action]

The LAN of FIG. 5 in which a plurality of small computers 1 are connected to the busbars L1 and L2 via the directional bridge circuit 10 respectively.
In, when the information signal is not transmitted, the open / close switch SW1 is opened. Therefore, the impedance of each small computer 1 viewed from the busbars L1 and L2 is maintained at an appropriate high level without escape from the decrease due to the insertion of the blow resistances R3 and R4. At the time of transmission, a small computer 1 that sends out an information signal,
For example, the open / close switch for the small computer A shown in FIG.
Close SW1. Since there is no incoming signal in this small computer A, the output of the detection terminal DT in FIG. 6 is zero. By using the zero output of the detection terminal DT, it is possible to prevent the transmission information signal from flowing into the self circuit. In the example of FIG. 1, the gate circuit 20 described below is used to prevent this sneak, but the sneak prevention means is not limited to the gate circuit. The transmitted information signal is received by all the small computers 1 connected to the bus lines L1 and L2, so that the small computer specified in the information signal responds to the designation by transmitting the information signal to itself. Can be captured. That is, multiple access (CS
MA) function can be achieved by a two-wire cable. When a signal from the outside arrives at the small computer 1 during the transmission operation for some reason, the directional bridge circuit 10 of the small computer 1 regards the arrival of the signal as the impedance change of the external circuit, and Output is generated at the detection pin DT. The small computer 1
Can send the collision signal CD shown in FIG. 4B and interrupt its own information signal sending in accordance with the detection terminal output DT. That is, the same signal collision detection (CD) function as the conventional
It can be achieved by a wire cable. Thus, the object of the present invention is to provide a "two-wire intra-region information communication network having a high input impedance of a small computer and capable of detecting a signal collision". Preferably, each small computer 1 for the buses L1 and L2
Is connected / disconnected between the small computer 1 itself and the equivalent impedance Z of the small computer by the change-over switch SW2 in FIG. 1 to compensate the fluctuation of the input impedance.

【Example】

In the embodiment of the present invention shown in FIG. 1, the output of the communication control circuit 5 of each small-sized computer 1 is added to the connection points P1 and P2 of the directional bridge circuit 10 via the driver 12, and the connection points P1 and P1 thereof are added. The reception signal reaching P2 is applied to the communication control circuit 5 via the reception receiver 13 and the gate circuit 20. The detection terminal DT of the directional bridge circuit 10 is added to the detection receiver 14. At the time of normal transmission, the zero output at the detection terminal DT is applied to the detection receiver 14, and the monostable circuit MS1 applies a zero voltage signal to the communication control circuit 5 according to the zero output. As a result, the transmitting small computer confirms the normal transmission and continues the transmission. If a signal comes from the outside for some reason during normal transmission and a collision occurs, a finite voltage appears as a detection signal at the detection terminal DT, and the monostable 17 performs communication control of the finite voltage signal according to the detection signal. Add to circuit 5. The communication control circuit 5 detects a collision by the simultaneous occurrence of the output to the driver 12 and the existence of the finite voltage signal from the monostable 17. In response to the collision detection, the communication control circuit 5
The transmission is stopped and the collision signal CD is sent, and the system enters the collision avoidance process. During normal reception, the finite value output at the detection terminal DT
It is applied to the monostable circuit MS1 and the detector 15 via the detection receiver 14. The detector 15 rectifies the output of the detection receiver 14 and adds it to the comparator 16, inspects by the comparator 16 whether it is a predetermined value or more, and if the output of the detection receiver 14 is a predetermined value or more, a gate circuit. 20 is opened, and the output of the reception receiver 13, that is, the received information signal is applied to the communication control circuit 5. The monostable circuit 18 shown in FIG. 1 is for performing a silent time (for example, about 16 μS) at the end of reception and discharging the smoothing capacitor of the rectifier circuit of the detector 15. In the illustrated embodiment, the open / close switch SW1 and the changeover switch SW2 are controlled by the relays RL1 and RL2, respectively, but the present invention is not limited to the use of this relay. [Experimental example] Five personal computers were connected in the manner shown in FIGS. 1 and 5 to fabricate a two-wire intra-region information communication network according to the present invention. As a result of measuring the line utilization rate (throughput) when communicating between each personal computer for this prototype, a line utilization rate of 80% or more was confirmed for the transfer of actual data. This value is equivalent to the conventional 4-wire star LAN system, and is superior to the so-called ACK line utilization rate.

【The invention's effect】

As described in detail above, the two-wire type intra-regional information communication network according to the present invention includes a plurality of small computers connected via a two-wire cable and a directional bridge circuit including a series resistor, a tap resistor and a detection terminal. Since it is connected between a small computer and a two-wire cable, a CSMA / CD system LAN can be realized by using the same two-wire cable as a normal telephone line, and it has a remarkable effect of providing highly efficient transmission at low cost.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of the present invention, FIGS. 2 and 3 are explanatory views of a conventional example, FIGS. 4A and 4B are time charts of information signals, and FIGS. 5 and 6 are It is an explanatory view of a two-wire intra-region information communication network according to the present invention. 1 ... Small computer, 2 ... Network hub
Unit NHU, 3 ... communication cable, 5 ... communication control circuit, 10 ... directional bridge circuit, 11 ... load, 12 ... driver, 13 ... reception receiver, 14 ... detection receiver, 15
...... Detector, 16 …… Comparator, 17 …… Monostable circuit 1, 18 …… Monostable circuit 2, 20 …… Gate circuit.

Claims (2)

[Claims] 1. A plurality of small computers connected to a bus through a two-wire communication cable, two series resistors serially connected to the two wires of the communication cable at the output end of each small computer, and the two series resistors. Directional bridge circuit having two plow resistors selectively connected in a bridge shape and two detection terminals in contact with both plow resistors, and an open / close switch connected between the series resistor and the plow resistors And opening the open / close switch at the output end of a small computer not transmitting to separate the plow resistance from the series resistance, and closing the open / close switch at the output end of the small computer during transmission to close the bridge. Completion of connection and occurrence of signal collision due to a signal other than the signal sent by the transmission is detected by a voltage change between the both detection terminals 2
A line-type information communication network within the area. 2. The intra-region information communication network according to claim 1, wherein a two-pole changeover switch selectively connects the communication cable connected to the bus bar to the small computer and a pseudo circuit of the small computer. A two-wire intra-region information and communication network equipped with.