Vehicle communication system

Details Vehicle communication system Vehicle communication system

1998-01-30

2001-06-12

Pham, Chi (Department: 2631)

Pulse or digital communications

Synchronizers

Synchronization failure prevention

C375S213000, C307S010100

Reexamination Certificate

active

06246734

ABSTRACT:

FIELD OF INVENTION
The present invention relates to a vehicle communication system for use in a motorcycle, car, or similar vehicle, and particularly to a vehicle communication system suitable for high speed communication with reduced pulse signal waveform distortion.
BACKGROUND OF THE INVENTION
Japanese Patent publication No. Hei 7-22431, discloses a mobile communication system in which various transceiver unit (node) sets are connected by single signal lines. Reduction in weight and cost, as well as improvement in communication efficiency, is made possible by simplifying the previous communication system construction.
A circuit diagram of a conventional vehicle communication system for carrying out communication between nodes is shown in
FIG. 6. A
balanced cable
5
is used as the signal line, which is a twisted pair cable. Node
16
has the same configuration as node
12
.
Node
12
is equipped with a transmission circuit
121
, a reception circuit
125
, and a microcomputer
3
. The microcomputer
3
outputs a transmission signal through an output terminal
3
a,
and this transmission signal acts as a control signal for simultaneously controlling both transistors Q
1
and Q
3
. The reception circuit
125
is equipped with a comparator CP for outputting a reception signal to the input terminal
3
b
of the microcomputer
3
, and resistors R
1
, R
3
.
The non-inverting input terminal of the comparator CP (+terminal) is connected to terminal
12
a
through resistor R
1
, while the inverting input terminal (−terminal) is connected to terminal
12
b
through resistor R
3
.
The transmission circuit
121
is equipped with transistors Q
1
and Q
3
, an inverter N
1
, an inverter N
3
, diodes D
1
-D
4
, and pull-up resistors RL, RL. The inverter N
1
generates a control signal for transistor Q
1
by inverting the signal transmitted by the microcomputer
3
through the output terminal
3
a.
The inverter N
3
generates a control signal for transistor Q
3
by inverting the control signal output from inverter N
1
.
A power supply voltage Vdd is applied to the collector of transistor Q
1
through a pull-up resistor RL, and the collector of transistor Q
3
is connected to ground through a pull-up resistor RL. The core of one cable
5
a
of the balanced cable
5
is connected to the collector of the transistor Q
1
through terminal
12
a,
while the core of the other cable
5
b
of the balanced cable
5
is connected to the collector of transistor Q
3
through terminal
12
b.
In node
12
, when the microcomputer
3
sets the output terminal
3
a
to an H (high) level by transmitting an H level signal, the transistors Q
1
and Q
3
are both turned off. As a result, the potential of terminal
12
a
of node
12
, the cable
5
a
that is connected to terminal
12
a
, and terminal
16
a
of node
16
connected to the cable
5
a
becomes the power supply voltage Vdd and has an H level signal. Further, the potential of terminal
12
b
of node
12
, the cable
5
b
that is connected to terminal
12
b
and terminal
16
b
of node
16
connected to the cable
5
b
becomes the ground potential (0 volts) and has an L level signal.
If a signal is transmitted from node
16
via the balanced cable
5
, the comparator CP of node
12
obtains a reception signal (H level signal) by differentially amplifying the signal from the balanced cable
5
and outputs an H level signal to the microcomputer
3
.
On the other hand, if the output terminal
3
a
is set to an L (Low) level as a result of the microcomputer
3
transmitting an L level signal, transistors Q
1
and Q
3
are turned on together. As a result, the potential of terminal
12
a
of node
12
, the cable
5
a
that is connected to terminal
12
a,
and terminal
16
a
of node
16
connected to the cable
5
a
becomes the ground potential (0 volts) and has an L level signal. Further, the potential of terminal
12
b
of node
12
, the cable
5
b
connected to terminal
12
b
and terminal
16
b
of node
16
connected to the cable
5
b
becomes the power supply voltage Vdd and has an H level signal.
If a signal is transmitted from node
16
via the balanced cable
5
, the comparator CP of node
12
obtains a reception signal (L level signal) by differentially amplifying the signal from the balanced cable
5
and outputs an L level signal to the microcomputer
3
.
When the output terminal
3
a
switches from an L level to an H level, the rise and fall times of a pulse signal are determined by a pull-up resistor RL, and the distributed capacitance of the signal line, etc. Accordingly, when the signal line is long the pulse signal wave shape is distorted.
In order to solve the aforementioned problems, Japanese Patent Laid open Publication No.-Hei 5-292101 discloses a communication system for a vehicle provided with a pull-up resistor and a signal line connected to a transistor, for carrying out communication between respective nodes through the signal line by controlling the transistor. The transistor is also provided with charge and discharge units for causing the distributed capacitance of the signal line to be discharged by making a stored charge by-pass a pull-up resistor, or causing the distributed capacitance of the signal line to be charged by making a charge by-pass a pull-up resistor. The charge and discharge units cause charge or discharge only for a fixed period of time that is less than 1 bit length of a signal from the instant when the transistor is switched from on to off.
The charge and discharge units provide an improved system over the case where the distributed capacitance of the signal line is discharged by passing a stored charge through a pull-up resistor or charged by passing a charge through a pull-up resistor. The rising (and falling) of a signal can be quickened, and pulse signal waveform distortion can be decreased by use of the charge and discharge units.
Further, since the transistor is in an off state for a time of at least 1 bit length after the transistor switches from on to off, charging or discharging can be carried out by by-passing the pull-up resistor during the transistor off state period. Since the transistor is in the off state, large current does not flow across the transistor collector and emitter, thereby preventing damage to the transistor. This benefit is sustained even when resistance of the charge and discharge unit is low at the time of charge and discharge.
However, if charging or discharging by the charge and discharge units is completed during switching of the reception circuit, noise enters the signal line. Accordingly, there is a danger of the on/off switching of the reception circuit becoming slow due to the effect of a level value of a signal on the signal line momentarily becoming reversed (inverted) and then returning to its original level value.
SUMMARY OF THE INVENTION
The present invention is intended to solve the above described problems, and provides as its object a vehicle communication system having a pull-up resistor and a signal line connected to a transistor, for carrying out communication between respective nodes by controlling the transistor, in which pulse signal waveform distortion is small and suitable for high speed communication.
The vehicle communication system of the present invention is provided with charge and discharge units for causing the distributed capacitance of the signal line to be discharged by making a stored charge by-pass a pull-up resistor or causing the distributed capacitance of the signal line to be charged up by making a charge by-pass a pull-up resistor. The charge/discharge units enable charging or discharging for only a fixed period of time shorter than 1 bit length of the signal from when the transistor is switched from on to off. For a node connected through the signal line, this fixed period of time is also longer than the time required for the reception circuit that obtains a reception signal from the signal line to switch on or off.
Charging or discharging by the charge discharge unit for longer than the switching time allows the system to fo

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