JPS61289750A - Data communication equipment - Google Patents

Abstract

PURPOSE:To prevent a fault voltage from being sent to a data communication line by detecting a terminal voltage of a transmitter and a receiver before a switch switching the transmitter receiver and a communication line is closed and inhibiting the closing of the switch if the terminal voltage is abnormal. CONSTITUTION:The data communication line 1 is connected to the receiver 5 and the transmitter 6 via the switch 3 and the switch 3 is disconnected so long as no connection signal comes from a control circuit 15. The input of the receiver 5 and the output of the transmitter 6 are connected to a voltage comparator 13 of a fault detection circuit via a switch 9 and the switch 9 is controlled for the switching by the control circuit 15. The control circuit 15 closes the switch 9 before the start of operation to detect the said terminal voltage by using the voltage comparator 13 and inhibits the closing of the switch 3 if the voltage is abnormal. Thus, no abnormal voltage is sent to the data communication line.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data communication device connected to a serial data communication line. In particular, the present invention relates to a device that prevents abnormal voltage from being sent from a data communication device to a data communication line and interfering with communications of other devices.

〔overview〕

The present invention provides a data communication device equipped with a switch that opens and closes between a transmitter and a receiver of the data communication device and a data communication line. If the terminal voltage is abnormal, the switch is prohibited from closing, thereby preventing abnormal voltage from being sent to the data communication line.

[Conventional technology]

As shown in FIG. 3, a conventional serial data communication network is comprised of a data communication line 43 through which communication data passes and a plurality of serial data communication systems 44 having serial data communication devices connected thereto. At this time, data communication line 4
3 and the serial data communication device are always electrically connected as shown in Figure 4, but as shown in the figure, when the system is powered off and is not operating, it is connected by switch 45. It is separated from the data communication line 43,
There is a method that connects when the system starts operating, such as when the power is turned on.

[Problem that the invention seeks to solve]

In the conventional serial data communication devices mentioned above, if there is a potential failure in the transmitter/receiver of any serial data communication device that deviates from the communication electrical standards, such as current draw or voltage clamp, the connection with the data communication line will be interrupted. If this is done using the method shown in FIG. 4 or 5, the data communication line will not be able to maintain a normal signal level due to a malfunctioning transmitter/receiver, and data communication will not be performed normally.

The present invention solves the above-mentioned conventional problems.

An object of the present invention is to provide a data communication device that improves the reliability of data communication by prohibiting connection to a line when there is a failure in the serial data communication device.

[Means for solving problems]

The present invention includes a first switch provided between receiver input and transmitter output terminals and a data communication line, and a control circuit that closes the switch before the start of operation and opens the switch after the end of operation. In the data communication device, a voltage comparator is connected to the terminal via a second switch, and the second switch is controlled to open and close by the control circuit. It is characterized by comprising means for previously closing the second switch, detecting the voltage at the terminal by the voltage comparator, and prohibiting closing of the first switch if there is an abnormality in the voltage. shall be.

[Effect]

The second switch is closed prior to closing the first switch, and the voltages at the transmitter output and the receiver input are monitored by a voltage comparator. If this voltage is normal, the first switch is closed and communication begins.

When the voltage is abnormal, the operation of the first switch is prohibited to prevent abnormal voltage from being sent to the data communication line.

〔Example〕

Next, the present invention will be explained with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. A switch 3 controlled by a control circuit 15 is connected through a signal line 2 from a data communication line l to which a serial data communication system having a plurality of serial data communication devices is connected. A receiver 5 and a transmitter 6 are connected to the switch 3.
is connected. Here, the switch 3 remains in a disconnected state unless a connection signal is received from the control circuit 15 before and after the system is powered on.

The output of the transmitter 6 is connected to the signal line 4 and also to the input of the receiver 5, and the signal line 4 is connected to the voltage comparison circuit which is a component circuit of the abnormality detection circuit 12 through a switch 9 controlled by a control circuit 15. The signal is input to the device 13. Further, the output 25 of the comparison voltage generation circuit 14 is connected to the other input of the voltage comparator 13.

Here, the output of the comparison voltage generation circuit 14 is connected so as to be controlled by the output 24 of the control circuit 15.

The transmitter 6 receives the transmission signal line 18 and the output 20 of the control circuit 15 through the gate 7 . Further, the transmission control signal 19 and the output 21 of the control circuit 15 are coupled to the control input of the transmitter 6 through the gate 8 . This gate 7.8 allows the state of the transmitter 6 to be forcibly controlled by the control circuit 15. The output of the pull-up circuit IO is input to the voltage comparator 13 via the switch 11. Voltage comparator 1
3 and the external activation signal line output 22 are input to the control circuit 15, and the line connection status signal from the control circuit 15 is sent to the signal line 2.
Output in 3. FIG. 2 is a flowchart of the processing procedure of the control circuit 15, which is one of the components of the present invention, and the present invention will be explained in detail using this flowchart. Although not shown, the control circuit 15 is activated when the power is turned on. The switch 3 is in a disconnected state before the power is turned on, and from this state, the control circuit 15 is activated when the power is turned on.

When the power is turned on, the control circuit 15 connects the abnormality detection circuit 12 and the signal line 4 through process 27 in FIG. 2 in order to inspect the output of the transmitter 6 and the input of the receiver, and enters the transceiver inspection process. . In processes 28 to 33 in FIG.
It is checked whether the voltage level of No. 4 satisfies a predetermined standard value, thereby confirming the output level of the transmitter. At this time, even if the input to the receiver is abnormal, the voltage level will no longer satisfy the standard value, so it can be confirmed at the same time.

If the standard value is not satisfied, the switch 3 remains disconnected and is not connected to the data communication line 1, and the signal 23 notifies the system that communication is not possible, and the operation of the control circuit ends. If it is normal, the process proceeds to step 34, in which the pull-up circuit 10 is connected by the switch 11 in order to test whether the transmitter 6 is in the OFF state. Then, in steps 35 to 37, it is checked based on the voltage level whether the transmitter 6 is in the off state. If the predetermined standard voltage cannot be satisfied, the switch 3 will remain disconnected, the voltage communication line 1 and the transmitter/receiver will not be connected, and the communication power (impossible) for the serial data communication system This is known in the processing 42 via the signal line 23.
5 stops operation.

If the transmitter 6 and receiver 5 are normal in processes 27 to 37, the switch 3 is connected to enable normal serial voltage communication in processes 38 and 39, and the transmitting and receiving signals are connected for the first time. Voltage communication line 1 is connected. Then, it notifies the system that communication is possible. Control circuit 15
ends the operation in this state.

〔Effect of the invention〕

As explained above, the present invention automatically checks the normality of the transmitter/receiver of the serial data communication device by connecting the data communication line and the serial data communication device using a predetermined procedure.
Do this after approval. Therefore, it is possible to improve the reliability of data communication through the data communication line and to clarify the nature of the failure in the serial data communication device.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a serial data communication device according to the present invention. FIG. 2 is a flowchart of the processing procedure of the control circuit of the embodiment shown in FIG. FIG. 3 is a block diagram of a conventional common serial data communication system. FIG. 4 is a connection diagram between a conventional data communication line and a serial data communication device. FIG. 5 is a connection side view different from the connection example shown in FIG. 4. 1... Data communication line, 3.9.11.45... Switch, 5... Receiver, 6... Transmitter, 10... Pull-up circuit, 12... Abnormality detection circuit , 13... Voltage comparator, 14... Comparison voltage generation circuit, 15... Control circuit, 27-42... Processing. Patent applicant NEC Corporation - Agent Patent attorney Nao Takashi Ide 1 Figure M 2 Figure

Claims (1)

[Claims] (1) A first switch is provided between the receiver input and transmitter output terminals and the data communication line, and a control circuit is provided that closes this switch before the start of operation and opens it after the end of operation. In the data communication device, a voltage comparator is connected to the terminal via a second switch, and the second switch is controlled to open and close by the control circuit. the second switch is closed, the voltage at the terminal is detected by the voltage comparator, and if there is an abnormality in the voltage, the first switch is prohibited from closing. data communication equipment.