JPH08194567A - Interface circuit - Google Patents

Abstract

PURPOSE: To normally accept a communication signal by eliminating the disturbance waveform higher than the prescribed voltage in the two-wire serial data communication and taking out the only communication signal from a cable. CONSTITUTION: The voltage limiter by a Zener diode 11 eliminates the disturbance waveform higher than the prescribed voltage of the communication signal inputted from input terminals 9 and 10. The operation voltage at this time is obtained by selecting the operation voltage of the Zener diode 11 suitable for the voltage of the normal signal. Then, the circuit discharged from a variable resistor 13 eliminates the low frequency component of the voltage differentiated by a capacitor 12 and takes out the only normal waveform component. Then, a diode 14 and a Schmidt trigger circuit 15 reshapes the waveform to recover the normal communication signal waveform at the output to an output terminal 16. Thus, the communication signal can be normally accepted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computer-based serial data communication system, and more particularly to an interface suitable for a two-wire serial data communication system message monitor.

[0002]

2. Description of the Related Art As shown in FIG. 1, in a two-wire serial data communication system, the transmission unit 2 or the reception unit 3 and the cable 5 are disconnected when the switching unit 4 is switched, and disconnection noise is generated during the switching operation. appear. Disturbance noise is generated on the cable when disconnected. There is no example of an interface circuit that inputs a message while connected to a cable.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an interface circuit in a serial data communication system for solving the problem that a communication signal is disturbed and a communication signal cannot be normally received. It is in.

[0004]

The concept of the present invention will be described with reference to FIG. A normal communication signal is a rectangular wave, and the amount of change in the waveform and the peak value are specified. By using the voltage limiter circuit 6 and the high-pass filter circuit 7, a low-frequency disturbance and a steep disturbance at the time of switching operation can be eliminated, and the waveform shaping circuit 8 can restore a normal communication signal.

[0005]

[Function] A normal communication waveform is a rectangular wave having positive and negative polarities, and the peak value is also specified. First, the voltage limiter circuit 6
The disturbance component above the specified value is removed by. Next, the high-pass filter circuit 7 extracts only the high-frequency component of the normal communication waveform component. Thereafter, the waveform shaping circuit 8 can restore the original normal communication signal.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG.
The communication signal input through the input terminals 9 and 10 is subjected to the voltage limiter by the Zener diode 11 to remove the disturbance waveform above the specified voltage. The operating voltage at this time can be obtained by selecting the operating voltage of the Zener diode suitable for the voltage of the normal signal. Next, a low frequency component is removed by a circuit for discharging the voltage differentiated by the capacitor 12 from the variable resistor 13, and only a normal waveform component is taken out. Next, the diode 14 and the Schmitt trigger circuit 15 shape the waveform to restore the original normal communication signal waveform and output it to the output terminal 16.

[0007]

In the two-wire serial data communication system, a normal communication signal can be taken out by connecting the input terminal to the cable, and the communication signal can be input to another computer by using the output, and an external monitor can be used. Can be expanded.

[Brief description of drawings]

FIG. 1 is a block diagram of a two-wire serial data communication system.

FIG. 2 is a block diagram of an interface circuit of the present invention.

FIG. 3 is a circuit diagram of an interface of the present invention.

[Explanation of symbols]

11 ... Zener diode, 12 ... Capacitor, 13 ...
Variable resistor, 14 ... Diode, 15 ... Schmitt trigger circuit.

Claims (1)

[Claims] 1. A computer having a transmitter, a receiver, and a switch, performs data communication by a two-wire serial data communication system connected by a cable, and the switch is used in the two-wire serial data communication system. An interface circuit that eliminates waveforms other than communication signals due to operation and disturbance and extracts only communication signals from the cable.