JP2587125Y2 - Communication unit of multiplex communication system - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication unit used in a multiplex communication system in which a plurality of communication units communicate via a common communication bus.

[0002]

BACKGROUND ART is a conventional multiplex communication system is, for example, as shown in FIG. This system is
Communication system, and a CPU 6 to be described later has a master station and a communication unit.
Tsu door ₁ 1, 1 ₂ becomes the slave station. Figure 3 shows the case of a multiplex communication system for a vehicle, 1 _1, 1 ₂ is the communication unit, not shown is also provided two or more, each power input terminal 2, the transmitting terminal 3 and the receiving It has a terminal 4. 5 is a transmitting terminal 3 and a receiving terminal 4 of each communication unit.
Is a common communication bus, and 6 is a CP that controls the entire system.
U, 7 each communication unit 1 _1, 1 ₂ of a battery for supplying power to the power input terminal 2, 8 denotes a power supply switch such as an ignition switch.

In the communication units 1 ₁ and 1 ₂ , an output circuit 9 has a power supply terminal 10, an output terminal 11, a ground terminal 12 as a reference potential terminal, and a signal input terminal 13. 1
4 PWM encoder for input to the signal input terminal 13 and the PWM signal pulse width modulates the transmission data, R _1, R ₂ is connected to the load resistor between the output terminal 11 and the transmission terminal 3, 15 receive pin 4 is a receiving circuit that receives a signal from the control unit 4.

Reference numeral 16 denotes a constant voltage circuit for converting the voltage of the battery 7 applied to the power input terminal 2 to a constant voltage, 17 a capacitor for smoothing the output voltage of the constant voltage circuit 16 to form a power supply voltage V _DD, and 18 a constant voltage. A power supply circuit composed of a circuit 16 and a capacitor 17 is a load to which a power supply voltage V _DD is applied.
For example, it includes a drive circuit of a display unit that displays the reception data of the reception circuit 15 and the like.

As shown, the output circuit 9 comprises a P-channel MOSFET (hereinafter simply referred to as a transistor) Q ₁ and an N-channel transistor Q ₂ which are complementarily connected to each other. Output terminal 1
1 is connected to the gate electrodes G of the transistors Q ₁ and Q _2.
1 and G ₂ are connected to the signal input terminal 13.

FIG. 4 is a cross-sectional view when the output circuit 9 is integrated into an IC. As shown in FIG.
⁺ , N ⁺ layers, the drain electrode D,
A source electrode S and gate electrodes G ₁ and G ₂ are formed to form a transistor Q ₁ . Also, by forming a P layer on the silicon substrate 20 and providing p ⁺ and n ⁺ layer regions therein,
A transistor Q ₂ is formed by forming a drain electrode D, a source electrode S, and gate electrodes G ₁ and G ₂ .

Next, the operation of the above configuration will be described.
You. Communication unit 1₁ Explain the case of sending
Then, this communication unit1 ₁ Output circuit 9 is a PWM
Encoder 14Signal input terminals 13 connected to
When “H”, the transistor Q_Two Turns ON and the output end
The child 11 becomes “L”. Also,The signal input terminal 13
bothTransistor Q when "L"₁ Is ON and output
The terminal 11 becomes “H”. Therefore, this output circuit 9 is actually
It qualitatively operates as an inverter. Also, communication unit
1₁ Is other than transmission (reception or transmission by another communication unit)
If receiving), the transistor Q₁ Gate electrode of
G₁ Signal input terminal 13 is "H" and the transistor
TA Q_Two Gate electrode G_Two Signal input terminal 13 is "L"
And the transistor Q₁ And Q_Two Are both OFF
The output terminal 11 becomes high impedance.

The signal obtained at the output terminal 11 is a load resistance R
_1, is sent to the communication bus 5 via the transmission terminal 3, CPU
6 is received. On the other hand, data output from the CPU 6 is not transmitted.
Is sent to the communication bus 5 and the communication unit 1 ₁ Is received by the receiving circuit 15 via the receiving terminal 4.

[0009]

However, in such a communication unit of a conventional multiplex communication system, the output circuit 9 including the transistors Q ₁ and Q ₂ is used. disconnection occurs at the point a, the power supply from the battery 7 to the communication unit 1 ₁ is cut off, the power supply voltage V _DD becomes zero, transistor Q
_1, Q ₂ but is OFF, the communication bus 5 at this time "H"
, As shown by the dotted line in FIG.
A current I flows from the transmission terminal 3 from the current I through the transistors Q ₁ through PN junction at the drain electrode D of the transistor Q _1, through the power supply terminal 10 of FIG. 3 from the gate electrode G _2, further load 19 Flows through to ground.

For this reason, there is a problem that the level of the communication bus 5 drops to a level close to the ground potential, and signal transmission becomes impossible.

The present invention has been made in view of such a conventional problem. The power supply voltage is constantly monitored, and when the power supply voltage falls to a predetermined level, the current flowing from the communication bus through the load described above. An object of the present invention is to solve the above problem by blocking the path of I.

[0012]

In this invention, a voltage detecting circuit for detecting a power supply voltage is provided, and a line between a power supply terminal of the power supply circuit and the output terminal of the output circuit or a line between the output terminal of the output circuit and the communication bus is opened and closed. A switch configured as described above is provided, and the switch is opened in response to a detection signal of the voltage detection circuit when the power supply voltage falls below a predetermined level.

[0013]

When the power supply voltage of the power supply circuit of one communication unit drops, the switch is automatically opened, so that the flow of current from the communication bus to the output circuit is prevented, and the communication bus maintains a normal state. .

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
FIG. 1 is a diagram showing an embodiment of the present invention. First, the configuration will be described. A voltage detection circuit 21 for detecting the level of the power supply voltage V _DD is provided, and this voltage detection circuit 21 outputs a detection signal 22 when the power supply voltage V _DD decreases to a predetermined level. Further, a switch circuit 23 for opening and closing a line between the output terminal of the power supply circuit 18 and the power supply terminal 10 of the output circuit 9 is provided. The switch circuit 23 is configured to be opened by the detection signal 22 of the voltage detection circuit 21.

The other parts are the same as those shown in FIG. 3. Corresponding parts have the same reference characters allotted, and description thereof will not be repeated. Further, the configuration of FIG. 1 is applied to all the communication units ₁₁ ,
It is common for 1 _2, 1 _3.

Next, the operation will be described. When normal communication is being performed, the switch circuit 23 is ON, and the same operation as that described with reference to FIG. 3 is performed.
Signals are transmitted and received between the communication units.

Here, when the power supply voltage V _DD falls to a predetermined level due to an accident such as a disconnection or a failure of the power supply circuit 18, the voltage detection circuit 21 detects this and the detection signal 2
3, the switch circuit 23 is turned off. Thus, the path of the current I described with reference to FIG.
Therefore, the potential of the communication bus 5 is normally maintained, and normal communication can be continued.

FIG. 2 shows another embodiment. This example is
The switch circuit 23 is provided on a line between the output terminal 11 of the output circuit 10 and the communication bus 5 connected to the transmission terminal 3, and is controlled by the detection signal 22 of the voltage detection circuit 21.

According to the above configuration, when the power supply voltage V _DD decreases, the switch circuit 23 is opened and the current I is blocked, so that the communication bus 5 is normally maintained.

[0020]

As described above, according to the present invention, according to the present invention, a voltage detecting circuit for detecting a power supply voltage is provided, and communication between the power supply terminal of the power supply circuit and the output terminal of the output circuit or with the output terminal of the output circuit is performed. A switch is provided to open and close a line to and from the bus, and a switch is provided. When the power supply voltage falls below a predetermined level, a detection signal of the voltage detection circuit is used to open the switch more. Thus, even if the power supply voltage is reduced due to the accident of the power supply circuit or the failure of the power supply circuit, it is possible to prevent the level of the communication bus from being lowered and the communication of the multiplex communication system from being damaged.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a communication unit of a multiplex communication system according to an embodiment of the present invention.

FIG. 2 is a block diagram of a communication unit of a multiplex communication system according to another embodiment of the present invention.

FIG. 3 is a configuration diagram of a communication unit of a conventional multiplex communication system.

FIG. 4 is a cross-sectional view when an output circuit in the communication unit is formed into an IC.

[Explanation of symbols]

1 ₁ , 1 ₂ communication unit 5 communication bus 9 output circuit 10 power supply terminal 11 output terminal 12 reference potential terminal 18 power supply circuit 19 load 21 voltage detection circuit 22 detection signal 23 switch circuit Q ₁ P-channel MOSFET Q ₂ N-channel MOSFET

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H04B 3/00-3/02 H04L 11/00 320 H03K 17/00

Claims (1)

(57) [Scope of request for utility model registration] An output circuit having a P-channel MOSFET and an N-channel MOSFET complementarily connected and having a connection point as an output terminal is connected between a power supply terminal and a reference potential terminal, and controls gate electrodes of both MOSFETs. Thus, a signal is transmitted from the output terminal to the communication bus, and the communication unit of the multiplex communication system includes a power supply circuit for supplying a power supply voltage to the power supply terminal and another load. A voltage detection circuit for detecting a power supply voltage of a circuit; and a circuit configured to open and close a line between the power supply circuit and the power supply terminal or between the output terminal and the communication bus, and when the power supply voltage falls below a predetermined level. And a switch circuit that is opened by a detection signal of the voltage detection circuit.