JPH0533089Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a duplex communication control device installed in a communication station that constitutes a duplex token bus type communication system, and particularly relates to a method for using a duplex bus. It's about improvement.

<Prior art> In the duplex communication control device provided at each communication station in a conventional duplex token bus type communication system, when a token is sent from its own communication station, the token is sent from the communication station that received the token. Token transmission is confirmed by detecting the carrier wave from one side of the duplex bus. on the other hand,
A communication station that receives a token addressed to its own station uses the duplex bus by alternately switching each time it transmits a token in order to use the duplex bus equally.

Here, if an abnormality such as a disconnection occurs in one of the duplex buses, the upstream communication station transmits a token to the normal bus, and this token is transmitted to the downstream communication station. On the other hand, if the downstream communication station happens to send a token to the bus on the abnormal side, this token will not be transmitted to the upstream side because the bus is abnormal.

At this time, the upstream communication station does not detect the carrier wave from the downstream communication station from which the token should be received, so it cannot confirm the transmission of the token it issued, and the token is further transferred to the normal side bus. keep it on top. On the other hand, the downstream communication station receives the token from the upstream and then sends this token downstream, so two tokens exist at the same time on the two buses of the duplex bus, and correct communication cannot be performed. A situation has arisen.

<Problem to be solved by the invention> The problem to be solved by the invention is to prevent two tokens from occurring on the duplex bus at the same time even if an abnormality occurs on one side of the duplex bus. The purpose is to realize a highly reliable communication system by using buses evenly.

<Means for solving the problem> The present invention, which has solved the above problems, uses a duplex communication control device installed in a communication station that constitutes a duplex token bus type communication system to transmit the token after sending it. A token transfer confirmation unit that confirms token transfer by confirming the carrier wave on the communication bus on the sending side; a bus selection unit that performs communication using the bus on the side that has received the token and transmits the token to the bus on the side that has received the token if there is no communication request; This is a duplex communication control device characterized by having a bus switching section that transmits a carrier wave signal for a certain period of time to the bus on the side that receives the token, and then switches to the other bus and transmits the token.

<Operation> In a communication system consisting of communication stations using the redundant communication control device of the present invention, a token sent from a certain communication station is transmitted via one bus, and when this token goes around on this one bus, The communication station with the smallest station number transmits a carrier wave for a certain period of time on the bus on the side that received the token, and can confirm token transmission to the communication station that sent the token.
Next, in order to use the duplexed buses equally, the same operation is performed for the other bus.

<Embodiment> FIG. 1 shows a communication station S including a redundant communication control device implementing the present invention.

In this figure, 1 is a duplex communication control device of the present invention, and 2 is a communication function unit unique to this communication station.

Furthermore, the redundant communication control device 1 has a redundant bus L.
1, L2 and selects one of the communication buses as appropriate and connects it to the communication function unit 2, and after sending the token, the state of the communication bus on the side that sent this token is determined via the bus selection unit 11. A token transmission confirmation unit 12 that monitors and confirms token transmission by detecting a carrier wave, and when a token addressed to the own station is received when the own communication station number is the smallest, sends a carrier wave to the bus on the side that received the token. Selection section 1
The bus switching section 13 instructs to switch the bus to be used.

An example of a system in which such communication stations are connected to a duplex bus is shown in Fig. 2, and Fig. 3 shows temporal changes in the states of signals on communication buses L1 and L2. The operation of this system will be explained using

In Figure 2, communication station S is connected to redundant buses L1 and L2.
1, S2, S3, and S4 are connected, and their respective communication station numbers are #1, #2, #3, and #4.

Assuming that the token is present at the communication station S1 at a certain point in time, the communication station S specifies the bus L1 using the bus switching unit 13 and the bus selection unit 11, and the token transfer confirmation unit 12 indicates that the token is transferred from the communication station S1 to the bus L1. to the communication station S2 via. Furthermore, this token is transferred from communication station S2 to communication station S3, and from communication station S3 to communication station S3.
from communication station S4, from communication station S4 to communication station S1
, via bus L1. When the token makes one round on the bus L1, the communication station S1 sends out a carrier wave to the bus L1 for a certain period of time from the bus switching unit 13. Communication station S4 that sent the token to communication station S1
The token transmission confirmation unit confirms the transmission of the token to the communication station S1 by receiving this carrier wave from the bus L1 on the side that received the token.

Next, the communication station S1 designates the bus L2 next and repeats the same operation in order to use the duplex buses L1 and L2 equally. After this operation has completed one cycle, the bus L1 is switched again and the same operation is repeated.

Here, if there is no bus abnormality, token transmission and carrier wave detection are performed on one bus first.
Once the bus is terminated, the other bus is switched to and the same operation is performed, so if a bus error occurs on either bus, communication is immediately performed to prohibit the use of the side where the error has occurred, and the two buses of the duplex bus are There can never be two tokens on top at the same time.

<Effects of the invention> In a communication system consisting of communication stations using the redundant communication control device of the present invention, a token sent from a certain communication station is transmitted via one bus, and this token is transferred on this one bus. After one cycle, the communication station with the lowest station number transmits a carrier wave for a certain period of time on the bus on the side that received the token, allowing the communication station that sent the token to confirm token transmission, and then spreads the duplex bus evenly. In order to use the other bus, the same operation is performed on the other bus, so even if an error occurs on one of the duplex buses, two tokens will not be generated on the duplex bus at the same time, and the duplex bus will be used evenly. A highly reliable communication system can be realized.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a communication station including the duplex communication control device of the present invention, Fig. 2 is a diagram showing a communication system having a plurality of communication stations, and Fig. 3 is a diagram showing the state of signals on the duplex bus. FIG. S, S1, S2, S3, S4...Communication station, L
1, L2... bus, 1... redundant communication control device,
11...Bus selection section, 12...Token transmission confirmation section, 13...Bus switching section.

Claims (1)

[Scope of utility model registration request] In a duplex communication control device installed in a communication station that constitutes a duplex token bus type communication system, after a token is sent out, token transmission is confirmed by checking the carrier wave on the communication bus on the side that sent this token. If there is a communication request in the own communication station when the token is received from one communication bus, this communication is carried out using the bus on the side that received the token, and if there is no communication request. a bus selection unit that transmits the token to the bus on the side that has received the token; and a bus selection unit that transmits a carrier wave to the bus on the side that has received the token for a certain period of time when its own communication station number is the smallest, and then switches to the other bus. A redundant communication control device comprising: a bus switching unit configured to transmit the token using a bus switching unit.