JP2535870B2 - Current-Pro-Cal area network system - Google Patents

Description

The present invention relates to a local area network system, and more particularly to a current loop transmission system.

[Conventional technology]

Traditionally, local area networks (LAN: Local
Optical cables, infrared rays, wireless, and conductor cables are used as transmission line media for Area Networks. In a LAN that uses a conductor cable as a transmission line medium, generally, a type that transfers data at high speed by a potential difference between two pairs of conductors (for example, DEC (DEC) Company, Intel (INTEL) Company in the US, There is a current loop type that transfers data by interrupting a current flowing through a loop-shaped conductor, such as Ethernet of Xerox Co., Ltd. A conventional example of the latter type is shown in FIG. .

Referring to FIG. 2, the current loop local area network system includes a current source I _S , a current loop line CL, and a station ST ₁ inserted in series in the middle of the current loop line CL.
~ ST _n (In Fig. 2, stations ST _{1 to} ST ₃ are shown, stations ST _{4 to} ST _3
n is omitted). Each station ST _{1 to} ST _n
It consists of transmission switches S _{1 to} S _n realized by electronic switches or relay contacts that interrupt the current according to the bit value of the transmission data, and photocouplers PC _{1 to} PC _n consisting of light emitting diodes and phototransistors. . It should be noted that the stations ST _{1 to} ST ₃ shown in FIG. 2 include circuits for realizing transmission / reception operations with respect to the local area network, but since they are not directly related to the present invention, their display and description are omitted.

Normally, when the stations ST _{1 to} ST _n do not perform the transmission operation, the transmission switches S _{1 to} S _n are turned on and the constant current I _C supplied from the current source I _S is continuously supplied to the current loop line CL. Station ST
Communication between _{1 ~ST n} is performed by the frame converting the packet configuration shown in Figure 3 to a serial bit stream. In Fig. 3, SYN, DA, SA, CONT, DATA, and END indicate the synchronization code (plural), destination address, source address, control information, data information, and end code, respectively, in this order. Sent.

As an example, when the station ST ₁ serves as a transmitting station and sends out a frame to the current loop line CL, the transmission bit value “1” turns off the transmission switch S ₁ , and the transmission bit value “0” indicates the transmission switch S ₁
By turning on, the constant current I _C flowing through the current loop line CL is interrupted. The stations ST _{2 to} ST _n , which are receiving stations, detect this intermittent current with the photocouplers PC _{2 to} PC _n , and receive the received signal.
Capture as R _{2 to} R _n . Each station ST _{1 to} ST _n is given a unique station address, and each station starts receiving a frame when the synchronization code SYN is detected, and the destination address DA of the received frame matches the address of its own station. For example, the frame is fetched and the frame reception is completed by the end code END. The method of allocating the transmission right to each station and the method of avoiding when the frames collide on the current loop line are not directly related to the present invention and therefore omitted.

[Problems to be solved by the invention]

In the conventional current loop local area network system described above, there is only one current source that supplies a constant current value to the current loop, and if this current source fails, it will be repaired or replaced in the local area. There is a drawback that the operation of the entire network system is stopped. In addition, in order to avoid system stoppage, a spare current source I _SUB is provided as shown in Fig. 4, and when the current source I _S fails, the changeover switch SW is used to switch to the spare current source I _SUB . However, there is a drawback that all communication is stopped from the occurrence of failure to the completion of switching.

[Means for solving problems]

An object of the present invention is to provide a current loop local area network system which eliminates the influence of a failure of a current source.

To this end, each of the plurality of stations is provided with a current source, and the transmitting station uses its own current source to transmit data to the transmission line. Further, each of the plurality of stations is provided with an inspection means for inspecting its own current source at the time of non-transmission operation so as to inspect whether a failure has occurred in its own current source.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. First
In the figure, the current loop local area network system of the present embodiment shows a current loop line CL and stations ST _{1 to} ST inserted in series in the middle of the current loop line CL.
_n (in FIG. ₁ , stations ST _{1 to} ST ₃ are shown, but stations ST _{4 to} ST _n are omitted). Since the stations ST _{1 to} ST _n have the same configuration, the station ST ₁ will be described below as a representative example.

The station ST ₁ is a current source I _S1 , a photocoupler PC _{1 including} a pair of a light emitting diode and a phototransistor, and is turned off when the station ST ₁ is not transmitting, and is set to a bit value of transmission data when the station ST ₁ is transmitting. It consists of a transmission switch S ₁ that consists of an electronic switch or relay contact that turns on or off in response to it, and a current check circuit TS ₁ that checks the good ratio of the current source I _S1 when transmission is not in progress. Although there is a circuit for realizing transmission / reception operations with respect to the local area network inside the stations TS _{1 to} TS _n shown in FIG. 1, their display and description are omitted because they are not directly related to the present invention. Also, the explanation of the method of acquiring the transmission right of each station to the network and the competition method of transmission on the network are omitted.

The operation of this embodiment will be described in detail below with reference to FIG. In FIG. _{1, it is} assumed that the communication between the stations ST _{1 to} ST _n is performed by a frame obtained by converting the packet having the configuration shown in FIG. 3 into a serial bit string. In addition, stations ST _{1 to} ST _n
Is assigned a unique station address, and each station takes in the frame when the destination address field DA of the received frame matches its own address.

When the stations ST _{1 to} ST _n do not perform the transmission operation, the transmission switches S _{1 to} S _n of each station are in the off state, and the current is not supplied to the current loop line CL, so that the photocoupler is connected.
The received signals R _{1 to} R _n, which are the outputs of PC _{1 to} PC _n , remain open. In this state, the current source I
_S1 ~I _Sn, it acceptability check by the current checking circuit TS ₁ ~TS _n conducted respectively, if the failure is detected, it prohibits transmission operation, warning that it is defective.

As an example of transmission / reception operation, a case will be described in which the station ST ₁ serves as the transmission station and sends out the data bit string of the frame to the current loop line CL.

At this time, the station ST ₁ connects the output of the current source I _S1 and the current loop line CL by turning on the transmission switch S ₁ by, for example, bit “1” according to the data bit value of the transmission frame. The current source I _S1 is not an ideal constant current source,
It has an output voltage value that varies depending on the load, and a positive potential is generated in the direction of the arrow of the current source. Due to this positive voltage, the light emitting diode of the photocoupler PC ₁ is maintained in reverse bias, and at the same time a constant current I _C is flown into the current loop line CL.

When a constant current I _C flows through the current loop line CL, stations ST _{2 to} S
When the light emitting diodes of the photocouplers PC _{2 to} PC _n of T _n are turned on and the phototransistors are turned on, the received signals R _{2 to} R _n are closed, so that the data bit “1” is transmitted to the station ST ₂ ~ Received at ST _n .

Further, when the transmission data bit of the station ST ₁ is “0”, when the transmission switch S ₁ is turned off, the supply of the constant current I _C to the current loop line CL is cut off, so that the stations ST _{2 to} ST _n The light-emitting diodes of the photocouplers PC _{2 to} PC _n are turned off and the phototransistors are turned off, so that the reception signals R ₂ to
When R _n is open, data bit “0” becomes station ST
Received from _{2 to} ST _n .

With the above operation, each station performs the receiving operation. Station ST ₂
~ ST _n starts receiving the frame when the synchronization code SYN is detected from the received data bit string, takes in the frame if the destination address DA of the received frame matches the address of the own station, and ends the code END Completes frame reception.

〔The invention's effect〕

As described above, according to the present invention, each station is provided with the current source forming the current loop, and the current forming the current loop is transmitted according to the transmission data bit value only while the transmitting station is transmitting the data bit. By providing the path, it is possible to prevent the operation of the entire system from being stopped due to the failure of the current source, which was the only one in the conventional current loop local area network. Moreover, even if the current source of a certain station fails,
Only during the transmission operation of the station, the transmission frame is garbled, and it is possible to prevent the communication between other stations from being disturbed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a first example of a conventional system, FIG. 3 is a diagram showing a field definition of a packet frame, and FIG. 4 is a conventional system. 6 is a block diagram showing a second example of FIG. I _S , IS ₁ , I _Sn ...... Current source, ST _{1 to} ST _n ...... Station, CL ...... Current loop line, I _C ...... Constant current, PC _{1 to} PC _n ...... Photo coupler, S
₁ ~S _n ...... transmit switch, R ₁ ~R _n ...... received signal, TS ₁ ~TS ₃
…… Current check circuit, I _SUB …… Preliminary current source, SW …… Switch.

Claims (1)

(57) [Claims] 1. A current loop local area network system which has a plurality of stations inserted in series in the middle of a loop-shaped transmission line, and which communicates by intermittently flowing a current flowing through the transmission line. Each of the stations is provided with a current source, and when transmitting data to the transmission line, the transmitting station itself supplies a current corresponding to the transmission data to the transmission line by using its own current source. Each of the stations is equipped with a checking means for checking the quality of its own current source during non-transmission operation, and detects that a failure has occurred in the current source.