JPH06152610A - Data transmitter - Google Patents

Abstract

PURPOSE:To transmit data at a high speed independently of the number of terminal equipments. CONSTITUTION:A line impedance measurement section 9 measures a change in the line impedance of a main trunk line 5 and sends a measured value to an impedance adjustment section 10. The impedance adjustment section 10 adjusts the resistance of a termination resistor depending on the value measured by the line impedance measurement section 9 so as to limit reflection distortion in the main trunk line 5 within a range not disturbing normal data transmission, thereby allowing normal data transmission.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission device in which a plurality of terminal devices are connected to a bus type transmission line.

[0002]

2. Description of the Related Art Generally, in order to drive a bus line having a large capacity load at a high speed, the characteristic impedance of the bus line must be uniform. However, when multiple terminals are connected to the bus line, the characteristic impedance is not uniform. In addition, in this case, there is a problem that the reflection distortion of the signal increases with the increase of the capacity of each terminal, which makes normal data transmission difficult. In order to solve this problem, a data transmission device as described in JP-A-2-198226 has been proposed. FIG. 4 shows the configuration of this data transmission device, and 5 is the main trunk line,
Both ends are terminated by the terminator 6. Terminals 1a, 1b and 1c are connected to the main trunk line 5 via a cord 7 and an outlet 2 respectively. Terminal device 1
Each of a, 1b and 1c is provided with an equivalent machine 8 having a function of detecting a preampule signal and a function of changing an equivalent parameter according to the detected value. When the cord 7 of the terminal device is connected to the outlet 2, the switch 3 switches to the cord 7 side to connect the main trunk line 5 to the cord 7. on the other hand,
If the cord 7 of the terminal device is not connected, the switch 3
Switches to connect the pseudo load terminator 4 to the mains 5.

Next, the operation of the above configuration will be described.
When transmitting data from the terminal device 1a to the terminal device 1b, the terminal device 1a transmits a preampule signal before performing the data transmission. The preamble signal is transmitted to the equivalent machine 8 of the terminal device 1b through the main trunk line 5 and the cord 7. This equivalent machine 8 is used during the preample signal reception period.
Using this signal, the equivalent parameters are set so that the influence of the reflection distortion of the transmission line is minimized. Therefore, since the setting of the equivalent parameter is completed in the terminal device 1b during the reception of the preampule signal, the data signal transmitted after the preampule signal can be received under the influence of the reflection distortion. Also, from the terminal device 1a to the terminal device 1
When the terminal device 1c is detached from the connector 2 during the data transmission to b, the switch 3 of the connector 2 to which the terminal device 1c was connected is switched, and the pseudo load terminator 3 is connected to the main trunk line 5. It By connecting the pseudo load terminator 3, the amount of change in the line impedance of the main trunk line 5 can be reduced. In this way, each terminal has an equivalent machine 8
By including the pseudo load terminator 4, reflection distortion of a signal can be suppressed and normal data transmission can be performed.

[0004]

In the conventional transmission device,
Since a pseudo load terminator and an equivalent machine are required for all outlets, an equivalent machine and a pseudo load terminator are required for each terminal when adding a terminal. Therefore, it takes time and effort to add a terminal device, and there is a problem in cost.

The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a data transmission apparatus which has a small amount of reflection distortion regardless of the number of terminals, is easy to add terminal apparatuses, and is low in cost. .

[0006]

As shown in FIG. 1, a transmission device of the present invention for solving the above-mentioned problems is such that an outlet 2 connects a cord 7 of a terminal device 1a, 1b and a main trunk line 5 to each other. The main trunk line 5 has a line impedance measuring unit 9, an impedance adjusting unit 10, and a terminating resistor 6 at both ends. The impedance adjusting unit 10 has a resistance adjusting function, the line impedance measuring unit 9 measures the line impedance of the main trunk line 5, and the terminating resistor 6 has a resistance value for impedance matching with the line impedance when there is no load. Have

In the above structure, the line impedance measuring section 9 measures the change in the line impedance of the main trunk line 5 and transmits the measured value to the impedance adjusting section 10.
The impedance adjusting unit 10 adjusts the value of the terminating resistance according to the value measured by the line impedance measuring unit 9, suppresses the reflection distortion of the main trunk line 5 to a range that does not hinder normal data transmission, and normalizes data transmission. To do.

[0008]

[Embodiment 1] FIG. 2 shows the configuration of Embodiment 1 of the present invention. A terminating resistor 6 is connected to a main trunk line 5 and a line impedance measuring section 9 is connected to the impedance adjusting section. 10 are connected. The line impedance measuring unit 9 includes comparators 11 and 12. The line impedance measuring unit 9 does not directly measure the impedance, but measures the voltage of the main trunk line 5. Comparator 11
Compares the voltage of the main trunk line 5 with the maximum reference voltage Vsh, and when the voltage of the main trunk line 5 is smaller than Vsh, outputs H and Vsh.
The output is L when it is larger than. Comparator 12
Compares the voltage of the main trunk line 5 with the minimum reference voltage Vsl, and outputs H and Vs when the voltage of the main trunk line 5 is higher than Vsl.
L is smaller than l. Input terminals of a motor driver 13 in the impedance adjusting unit 10 are connected to the output sides of the comparator 11 and the comparator 12, respectively. The motor driver 13 is the motor 15
In this driving, when the outputs of the comparators 11 and 12 are H and L, they are rotated in the forward direction, when they are L and H, they are rotated in the reverse direction, and when they are L and L, they are stopped. To control. The rotation of the motor 15 is transmitted to the variable resistor 16 through the power transmission unit, and the resistance value increases at the time of reverse rotation,
The resistance value decreases during normal rotation.

In the above configuration, in the initial setting, the variable resistor 16 is set to have a resistance value of about half the maximum resistance, and the resistance value of the variable resistor 16 and the termination resistor 6 are set.
Thus, the impedance mismatch with the line impedance is adjusted so that the reflection distortion during signal transmission does not interfere with normal signal transmission. Main trunk line 5 in this range
The maximum value of the voltage of Vsh is Vsh, and the minimum value thereof is Vsl. Here, the impedance is measured by measuring the voltage corresponding to the voltage drop of the terminating resistor without directly measuring the impedance, and adjusting the resistance value based on the measured voltage. When the voltage of the main trunk line 5 becomes higher than the maximum reference voltage Vsh due to the impedance of the line changing due to the attachment / detachment of the terminal device from the outlet, the motor 15 rotates in the positive direction, and the variable resistor 1
The resistance value of 6 decreases. As the resistance value decreases, the impedance mismatch falls within the allowable range, and the motor stops when the voltage of the main trunk line 5 becomes lower than Vsh.
On the other hand, when the voltage of the main trunk line 5 becomes smaller than the minimum reference voltage Vsl, the motor 15 rotates in the reverse direction and impedance mismatch again falls within the allowable range, and when the voltage of the main trunk line 5 becomes larger than Vsl, the motor 15 stops.

In this embodiment, since the terminating resistor is automatically adjusted according to the line impedance value of the main trunk line 5, reflection distortion of signals can be reduced and high speed signal transmission can be performed.

[0011]

Second Embodiment FIG. 3 shows the configuration of a second embodiment of the present invention, in which the same elements as in the first embodiment are designated by the same reference numerals. The line impedance measuring unit 9 in this embodiment includes an A / D converter 17 and a CPU 18. The CPU 18 has a conversion calculation function for providing a correlation between the amount of change in the resistance value of the variable resistor used in the first embodiment and the amount of change in the attenuation amount of the electronic volume 20. The impedance adjusting unit 10 includes a D / A converter 19 and an electronic volume 20.

In the initial setting of the above structure, the attenuation amount of the electronic volume 20 is set to about half of the maximum value,
The electronic volume 20 and the terminating resistor 6 are used to adjust the impedance mismatch with the line impedance so that the reflection distortion at the time of signal transmission does not interfere with the normal signal transmission.

The voltage A / D converter 17 of the main trunk line 5 converts the signal into a digital signal, which is transmitted to the CPU 18. CPU1
Reference numeral 8 constantly monitors changes in voltage, calculates the amount of attenuation of the electronic volume 20 when there is a change in voltage, and adjusts the electronic volume 20 so that impedance mismatch falls within an allowable range.
Change the output. The signal from the CPU 18 is converted into an analog value by the D / A converter 19 and then transmitted to the electronic volume 20. The electronic volume 20 changes the amount of attenuation according to the signal from the D / A converter 19.

In the second embodiment, since the electronic volume is used for impedance adjustment, a large component such as a motor is not needed, and the size can be reduced.

[0015]

As described above, according to the present invention, since the reflection distortion required for high-speed data transmission is reduced by automatically adjusting the termination resistance value, each terminal device has a similar load terminator. It is possible to provide a data transmission device that does not require an equalizer and can easily add a terminal device at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram of a data transmission device to which the present invention is applied.

FIG. 2 is a circuit diagram showing a configuration of a first embodiment of the present invention.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is a block diagram of a conventional example.

[Explanation of symbols]

 1a, 1b, 1c Terminal device 2 Connector 3 Switch 4 Simulated terminator 5 Main line 6 Terminator 7 Machine string 8 Equivalent machine 9 Line impedance measurement section 10 Impedance adjustment section 11,12 Comparator 13 Motor driver 14 Power transmission section 15 Motor 16 Variable resistor 17 A / D converter 18 CPU 19 D / A converter 20 Electronic potentiometer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryoyo Wakamatsu 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd.

Claims (1)

[Claims] 1. In a data transmission device in which a plurality of terminals are connected to a bus type transmission line for transmitting a digital signal, a line impedance measuring unit for measuring a change in line impedance of a network, and a line impedance measuring unit according to the measured line impedance value. A data transmission device, comprising: an impedance adjusting unit that corrects a termination resistance value so as to match the characteristic impedance.