JPH065844B2 - Communications system - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system, and in particular, a plurality of control circuits (hereinafter referred to as ECUs) are linked by a serial line for transmitting and receiving data to and from each other. The present invention relates to a serial communication system.

[Conventional technology]

Conventionally, NRZ is used as an encoding method in serial communication,
PWM, Manchester, etc. are used. In all of these, the data is represented by a combination of rectangular waves.

However, since the rectangular wave has steep rising and falling edges, the data represented by the combination of the rectangular waves contains many harmonic components. Since this harmonic is radiated and is superimposed on the radio band and adversely affects other devices, it is necessary to take measures against harmonic noise radiation. If the transmission line is separated from the radio antenna by a distance, the effect of noise is reduced, but it is inconvenient because the installation can be restricted.

As shown in FIG. 6, a method of removing harmonics with a CR filter or the like can be considered.
It is almost impossible to eliminate the influence over the entire range (700 kHz), and there is a problem that the signal itself changes with a filter having a large time constant.

Therefore, in order to solve the above-mentioned problem, instead of communicating a data waveform with a rectangular wave as it is transmitted by a processing circuit (hereinafter referred to as CPU), the data waveform is modulated into a trapezoidal wave and communicated with each ECU.
When a CPU receives a signal, it demodulates it into a rectangular wave that can be received by each CPU with reference to a constant threshold voltage preset in the receiving circuit. The operation is shown in FIGS. 7 (a), (b), and (c). Figure (a) shows the information signal I sent by the CPU.
FIG. 7B is a waveform diagram of W, FIG. 9B is a waveform diagram of the communication signal CW on the transmission path, and FIG. 9C is a waveform diagram of the demodulation signal RW received by the CPU. When the communication signal CW received from the threshold value S set in the receiving circuit has a high voltage, it is determined to be "H", and in the opposite case, it is determined to be "L", and each CPU has a rectangular wave which can be received. The demodulated signal RW is demodulated. By using a trapezoidal wave for the communication signal, this one can reduce the spectrum power of harmonics and suppress the noise emission to an extremely small amount.

[Problems to be Solved by the Invention]

However, when using a trapezoidal wave signal, an error is more likely to occur during modulation and demodulation than when using a rectangular wave signal,
In the above case, the modulation / demodulation error ΔT ₂ is | T ₀ −T from FIG.
_{2 |} given in, but there is a problem that significantly affects the demodulation error due to variations in threshold voltage and communication signal voltage. For example, when used for serial communication of an in-vehicle ECU, ON-OF of an actuator driven by a large current
GND between each ECU due to F and circuit constant error
Differences occur in the potential and the power supply voltage level, making it difficult to obtain a stable threshold value and signal voltage, resulting in a large modulation / demodulation error.

The present invention has been made in view of the above problems, and each ECU
An object of the present invention is to provide a communication system capable of reducing harmonic noise radiation due to communication signals between the ECUs and suppressing the modulation / demodulation error to a small value regardless of fluctuations in the GND potential difference and the power source potential difference between the ECUs.

[Means for Solving the Problems]

According to the present invention, in order to achieve the above object, the first and second control circuits are connected to each other through a common transmission line, and each control circuit outputs information represented by a rectangular wave signal to the common transmission line. In a communication system including a transmitter that sends out as a communication signal and a receiver that receives a communication signal transmitted through the common transmission line, the common transmission line includes first and second transmission lines. However, each transmitter in the first and second control circuits has
A first section that transforms the rectangular wave signal into a signal waveform having a predetermined slope at its rising edge and falling edge and sends the transformed signal as the communication signal to the first transmission path.
And a second transmitting means for transmitting an inverted signal of the communication signal to the second transmission path, wherein each receiver in the first and second control circuits comprises:
The magnitude of the communication signal transmitted from the transmitter in the other control circuit via the first and second transmission paths and the inverted signal are compared, and demodulated to information represented by the rectangular wave signal. The technical means of providing the receiving means is adopted.

[Action]

The first transmitting unit transforms the information composed of the rectangular wave into a signal waveform having a predetermined slope at the rising portion and the falling portion of the rectangular wave, thereby reducing the harmonic component and making the first communication signal. To the transmission line of. At the same time, an inverted signal composed of a waveform obtained by inverting the signal waveform of the communication signal is transmitted from the second transmission means to the second transmission line. Also,
When each ECU receives the signal, the receiving means compares the communication signal and the inverted signal in magnitude to demodulate the information into a rectangular wave.

〔Example〕

 The present invention will be described below with reference to the embodiments shown in the drawings.

FIG. 1 is a communication system diagram showing the first embodiment. First
In the figure, ECU1 to ECU4 are connected to each other by two bus lines, and each ECU incorporates a CPU and a common M section (transmission / reception circuit shown in FIG. 2 described later). Note that T _x is a CPU transmitting unit, R _x is a CPU receiving unit, TR is an M unit transmitting circuit unit, and RE is an M unit receiving circuit unit.

Next, FIG. 2 shows a circuit configuration diagram of the M portion in FIG. Second
In the figure, 1 is an input terminal, 2 and 3 are output terminals, 4 is a reception output terminal, and 10 and 20 are inverters. Also, 1
Reference numerals 1, 12, 21, 22 are constant current sources for supplying a constant current I in the arrow direction of FIG. Reference numerals 13, 14, 23 and 24 denote switches (hereinafter referred to as SW) which are controlled by given signals, and are OFF when the signal is “H” and ON when the signal is “L”.
It becomes a state. 15 and 25 are capacitors (hereinafter referred to as C)
And both capacitances C are equal.
Further, 16 is a PNP type transistor, and 26 is an NPN type transistor. Reference numerals 17, 18, 27 and 28 are resistors, and 30 is a comparator.

Next, the circuit operation of FIG. 2 will be described.

First, in the TR section, when "H" is input to the input terminal 1, the SW13 and SW24 are respectively connected to the inverter 1
The signal applied through 0 and 20 is "L", and the signals applied to SW14 and SW23 are "H". SW is OF when the applied signal is "H"
In the F state, when it is "L", it is in the ON state. Therefore, in this case, SW13 and SW24 are ON, SW14 and SW23.
Turns off.

When SW13 is ON and SW14 is OFF, the constant current source 1
From 1 the constant current I flows into one end of C15 and charging is started. Since the current and the capacitance are constant, the base potential of the transistor (hereinafter, referred to as Tr) 16 increases linearly. The emitter potential takes a potential higher than the base potential by V _BE, and linearly rises following the rise of the base potential,
It becomes V _CC .

At this time, since SW23 is OFF and SW24 is ON, the constant current source 22 discharges the constant current I from one end of C25. Due to the constant current and capacitance, Tr26
The base potential is lowered linearly, the emitter potential is lowered linearly to follow the base potential in V _BE potential lower than the base potential, a GND potential.

Conversely, if "L" is input to input terminal 1, SW
The signals applied to the switches 13 and 24 are turned off when the signal is "H", and the signals SW14 and SW23 are turned on when the signal is "L".

Constant current source 1 when SW13 is OFF and SW14 is ON
From 2, a constant current I flows from one end of C15, and discharge is started. Since the current and the capacitance are constant, the base potential of Tr16 drops linearly. The emitter potential is to follow the base potential in the V _BE potential higher than the base potential, V _CC
To descend linearly.

On the other hand, since SW23 is ON and SW24 is OFF,
A constant current I flows into one end of C25 and is charged by the constant current source 21. Tr2 due to constant current and capacitance
The base potential of 6 rises linearly. The emitter potential linearly rises from the GND potential following the rise of the base potential, and is kept at a potential V _BE lower than the base potential.

The slopes of rising and falling are ∫ idt = CV, and i is a constant value I and C is a constant value C.
It is expressed as / t = I / C.

Therefore, by the above operation, the rectangular wave signal input to the TR input terminal 1 is modulated into the corresponding trapezoidal wave signal, and the signal shaped into the trapezoidal waveform is output from the output terminal 2 and output from the output terminal 3. The same signal as that obtained by inverting the signal from the terminal 2 is output in the same phase.

In the RE section, the terminal of the comparator 30 is connected to the output terminal 2 of the TR section, and the terminal is connected to the output terminal 3 of the TR section. With this configuration, when the signal potential input to the side of the comparator 30 is higher than the signal potential input to the side, "H" is compared, and in the opposite case, "L" is determined and output from the reception output terminal 4.

From the above operation, referring to FIG. 1, ECU 1 to ECU 2
The flow of data when sending and receiving data to and from will be described. First, a rectangular wave signal is transmitted from T _X 1 of the CPU 1, and EC
The TR section of the M section built in U1 modulates the signal into a trapezoidal waveform and its inverted waveform, and outputs the signals to two bus lines, respectively. Each output data is received by the ECU 2, demodulated into a rectangular wave signal by the RE unit of the M unit built in the ECU 2 by comparison and determination, input to R _X 2 of the CPU 2, and received by the CPU 2. The first in FIGS. 3 (a), (b), and (c)
The signal waveform diagram of each point in the figure is shown. Figure (a) shows the signal waveform at point A, Figure (b) shows the signal waveform at points B ₁ and B ₂ , and Figure (c) shows the signal waveform at point C. Is. In addition, the modulation / demodulation error ΔT ₁ can be calculated from | T ₀ −
Given by T ₁ |.

Similarly, each ECU can mutually transmit and receive according to a protocol (transmission protocol).

In the above embodiment, the circuit structure shown in FIG. 2 can be regarded as the circuit structure shown in FIG. The reference numeral in FIG. 4 is the same as the reference numeral in FIG.
In the first embodiment, the trapezoidal waveform is shaped by using the constant current source, but the trapezoidal wave shaping circuit of FIG. 4 obtains a constant current by the constant voltage source and the constant resistance as shown in FIG. It may be the one of the second embodiment in which the trapezoidal waveform is shaped by using the above method.

Next, the operation of the trapezoidal wave shaping circuit shown in FIG. 5 will be described.
In FIG. 5, 50 is an input terminal, 52 to 59 are transistors (Tr), 51, 60 and 61 are resistors, and 62 is a resistor.
Is a capacitor (C), and 63 is an output terminal. The resistance values of the resistors 60 and 61 are R, and the capacitance of C62 is C.

A digital signal is input from the input terminal 50 to the protection resistor 51. When the signal is "H", Tr52 and Tr53 are turned on. Therefore, the collectors of Tr52 and Tr53 become "L". Therefore, Tr54 is in OFF state, Tr
55 is turned on. When Tr55 is in the ON state, the current that is substantially determined by V _CC / R by the resistor 61 is Tr5.
8 collector-emitter flow. Tr58 and Tr5
8 is a current mirror circuit, Tr59 is Tr58
A constant current similar to flows. At this time, since Tr56 is in the OFF state, no current flows from Tr57. When the electric charge is accumulated in C62, it is discharged by the constant current flowing in Tr59, and the potential of the output terminal 63 linearly drops.

On the other hand, when the signal input to the input terminal 50 is “L”, T
Both r52 and Tr53 are turned off. Therefore,
Tr54 is in the ON state, Tr55 is in the OFF state, and the current determined by the resistor 60 is approximately V _CC / R.
A constant current flows between the emitter and collector of No. 6 and Tr57 that forms a current mirror circuit with Tr56. At this time, no current flows through Tr59, so if no electric charge is stored in C62, C62 is charged and output terminal 63
The potential of rises linearly.

It should be noted that the slopes of rising and falling are ∫idt = CV, and it is understood that the slope V / t is constant because i is constant at V _CC / R.

By the above operation, the rectangular wave signal input to the input terminal 50 is modulated into the corresponding trapezoidal wave signal and output from the output terminal 63.

Although the bipolar transistor is used in the final stage of the TR section in the first and second embodiments, a FET or the like may be used.

Further, in the above-mentioned various embodiments, the communication signal is constituted by a trapezoidal wave, but, for example, it is constituted by a half wave of a sine wave, its rising portion of a rectangular wave, or the like.
It may be configured by a waveform having a smooth falling portion.

〔The invention's effect〕

As described above, in the present invention, by using a signal waveform having a predetermined slope in the rising portion and the falling portion in the communication signal, it is possible to reduce harmonic noise radiation and at the same time add a bus line. However, the communication signal with the inverted signal waveform is transmitted to the added bus line, and the two communication signals are compared and demodulated into a digital signal. Therefore, the GND potential between the ECUs and the power supply voltage fluctuate. Even if there is, there is an excellent effect that the influence can be relatively canceled and the modulation / demodulation error can be suppressed small.

[Brief description of drawings]

FIG. 1 is a communication system diagram showing the first embodiment, FIG. 2 is a transmitter / receiver circuit configuration diagram of the first embodiment, and FIGS. 3 (a), (b), and (c) are point signals of FIG. FIG. 4 is a waveform diagram, FIG. 4 is a simplified equivalent circuit diagram of FIG. 2, FIG. 5 is a trapezoidal wave shaping circuit diagram of the second embodiment, FIG. 6 is a principle diagram of a CR filter, and FIGS. 7 (a) and 7 (b). ) And (c) are signal waveform diagrams of the conventional one. 1 ... input terminal, 2,3 ... output terminal, 4 ... reception output terminal,
15, 25, 62 ... Capacitor, 16 ... PNP type transistor, 26 ... NPN type transistor, 17, 18, 2
7, 28 ... Resistor, 30 ... Comparator.

Claims (1)

[Claims] 1. A transmission in which first and second control circuits are connected to each other through a common transmission line, and each control circuit sends information represented by a rectangular wave signal to the common transmission line as a communication signal. And a receiver for receiving a communication signal transmitted via the common transmission path, wherein the common transmission path is composed of first and second transmission paths, and Each transmitter in the second control circuit has
A first section that transforms the rectangular wave signal into a signal waveform having a predetermined slope at its rising edge and falling edge and sends the transformed signal as the communication signal to the first transmission path.
And a second transmitting means for transmitting an inverted signal of the communication signal to the second transmission path, wherein each receiver in the first and second control circuits comprises:
The magnitude of the communication signal transmitted from the transmitter in the other control circuit via the first and second transmission paths and the inverted signal are compared, and demodulated to information represented by the rectangular wave signal. A communication system comprising receiving means.