JP3493650B2 - Communication device - 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 device that communicates via a bus.

[0002]

2. Description of the Related Art In a computer system, the entire circuit is CP
The U unit, the storage device unit, the input / output interface unit, and the like may be mounted separately on a plurality of printed circuit boards. The printed circuit boards are interconnected by connecting the connectors to which the printed circuit boards are connected to each other by a bus.

In a communication device using a bus, there are various factors that disturb the signal waveform. Hereinafter, this factor will be described.

FIG. 4 is a block diagram of a conventional example of a communication device using a bus. In FIG. 4 , a plurality of units 21 to 2 are provided on the bus 1.
n is multi-drop connected. Each unit 21-2
n communicates via a bus.

FIG. 5 is an equivalent circuit diagram of the bus 1. As shown in FIG. 5 , the bus 1 has its own inductance L and stray capacitance C.

When a unit is connected to the bus, the impedance decreases due to the capacitive component of the unit. As a result, the signal transmitted on the bus is reflected at the connection part of the unit. For example, in FIG. 4 , when a signal is sent from the unit 21 to the unit 22, each unit 22 to 2n
A reflected signal is generated at the connection part of. FIG. 6 is a signal waveform diagram at point B. At the point B, the signal reflected by the other units 23 to 2n reaches the point B before the reception signal of the unit 22 has finished transitioning from the high level to the low level. As a result, as shown in FIG. 6 , the received signal and each unit 2
Reflected signals from 3 to 2n are overlapped with each other and waveform distortion is increased. This may cause the receiving unit 22 to malfunction. In the example of FIG. 6 , the overlapped reflected signal is L
Exceeds the ow level threshold.

In order to prevent this, conventionally, the following restrictions have been made. (A) A special device with a small capacity is used for the unit. (B) Reduce the number of connected units. It has been desired that the influence of the reflected signal can be effectively suppressed without receiving these restrictions.

As described above, the reflected signal has an influence as a factor for disturbing the signal waveform transmitted through the bus.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and suppresses the influence of a reflected signal generated on a bus to reduce the disturbance of the signal waveform transmitted by the bus. It is an object to realize a communication device that can perform.

[0010]

The present invention is a communication device having the following configuration.

(1) In a communication device in which a plurality of units are multi-drop connected to a bus and communication is performed between the units via the bus, the line length of the bus between the units is set to a length that satisfies the following conditions. A communication device characterized by. (Transition time of bus transmission signal) ≤ (Time required for transmission signal to go back and forth between units with the shortest communication distance)

(2) The communication device according to (1), wherein the bus is composed of a wiring pattern formed in a zigzag shape on the substrate.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, the same parts as those in the previous figure are designated by the same reference numerals.
In FIG. 1, a plurality of units 21 to 2n are multi-drop connected to a bus 10. The line length of the bus 10 is set to satisfy the following conditions. (Transition time of transmission signal of bus 10) ≤ (time required for transmission signal to reciprocate between units having the shortest communication distance) An example of the bus 10 is a backplane bus.

For example, in FIG. 1, when a signal is sent from the unit 21 to the unit 22, a reflected signal is generated at the connecting portion of each unit 22 to 2n. FIG. 2 is a signal waveform diagram at point D. At the point D, the signal reflected by the other units 23 to 2n reaches the point D after the reception signal of the unit 22 has finished transiting from the high level to the low level. As a result, as shown in FIG. 2, the reflected signals from the respective units 23 to 2n are independent of each other without overlapping with the transition time of the received signal. As a result, the overlapping reflected signals do not exceed the low level threshold value, and the receiving side unit 22 does not malfunction.

FIG. 3 is a diagram showing a configuration example of the bus 10. As shown in FIG. 3, the bus 10 is composed of a wiring pattern formed on the substrate 11 in a zigzag shape.

[0016]

As described above, according to the present invention, the following effects can be obtained.

According to the invention of claim 1, the line length of the bus is set so that the transition time of the transmission signal of the bus is equal to or less than the round-trip time between the units of the transmission signal. Therefore, in the receiving unit, the reflected signal from another unit arrives after the transition time of the received signal ends. Since the reflected signals are independent, malfunction of the receiving unit can be prevented. As a result, the influence of the reflected signal generated on the bus can be suppressed.

According to the second aspect of the present invention, the bus is composed of a wiring pattern formed in a zigzag shape on the substrate. Therefore, it is possible to effectively utilize the small space to extend the line length of the bus.

As described above, according to the present invention, it is possible to provide a communication device in which the disturbance of the signal waveform transmitted on the bus is reduced by suppressing the influence of the reflected signal generated on the bus.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a signal waveform diagram of the embodiment of FIG.

FIG. 3 is a main part configuration diagram of the embodiment of FIG.

FIG. 4 is a configuration diagram of a conventional example of a communication device.

FIG. 5 is an equivalent circuit diagram of a bus.

FIG. 6 is a signal waveform diagram of the conventional example of FIG.

[Explanation of symbols]

10 bus 21-2n units

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Claims (2)

(57) [Claims] 1. In a communication device in which a plurality of units are connected to a bus in a multi-drop manner and communication is performed between the units via the bus, a line length of the bus between the units is set to a length that satisfies the following condition. Characterized communication device. (Transition time of bus transmission signal) ≤ (Time required for transmission signal to go back and forth between units with the shortest communication distance) 2. The bus is composed of a wiring pattern formed in a zigzag shape on a substrate.
The communication device described.