JPH11252133A - Communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the disturbance of a signal waveform transmitted in a bus by setting the line length of the bus to satisfy a specified condition. SOLUTION: A plurality of units 21-2n are multi-drop-connected to a bus 10. The line length of the bus 10 satisfies the condition of (transition time of the transmission signal of the bus 10)<=(time which a transmission signal requires for reciprocating between the units whose communication distances are the shortest). When the signal is sent from the unit 21 to the unit 22, for example, a reflection signal is generated in the connection part of the units 22-2n. At a point D, signals reflected in the other units 23-2n arrive at the point D after the reception signal of the unit 22 terminates shift from a high level to a low level. Thus, the respective reflection signals sent from the respective units 23-2n become independent without being overlapped with the shift period of the reception signal. Consequently, the overlapped reflection signals do not exceed a low level threshold and the reception-side unit 22 is prevented from malfunctioning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device for performing communication via a bus.

[0002]

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

[0003] In a communication device using a bus, there are various causes of a disturbance in a signal waveform. Hereinafter, this factor will be described.

(Factor 1) FIG. 8 is a configuration diagram of a conventional example of a communication device using a bus. In FIG. 8, a plurality of units 21 to 2n are connected to the bus 1 by multidrop connection. Each of the units 21 to 2n performs communication via a bus.

FIG. 9 is an equivalent circuit diagram of the bus 1. As shown in FIG. 9, the bus 1 has its own inductance L and stray capacitance C.

[0006] When a unit is connected to the bus, the impedance is reduced due to the capacitance 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. 8, when a signal is sent from the unit 21 to the unit 22, each of the units 22 to 2n
A reflected signal is generated at the connection portion of FIG. 10 is a signal waveform diagram at point B. At the point B, the signals reflected by the other units 23 to 2n arrive at the point B before the reception signal of the unit 22 transitions from the high level to the low level. As a result, as shown in FIG. 10, the received signal and the reflected signal from each of the units 23 to 2n overlap, and the waveform distortion increases. As a result, the receiving unit 22 may malfunction. In the example of FIG. 10, the overlapped reflected signal exceeds the Low level threshold.

In order to prevent this, the following restrictions have conventionally been imposed. Use a special device with a small capacity for the unit. Reduce the number of connected units. It has been desired that the influence of the reflected signal can be effectively suppressed without being limited by these restrictions.

(Factor 2) In a communication device using a bus, the transmission circuit of the unit is provided with a driver IC for transmitting a transmission signal to the bus. When a 1-bit driver input is kept stationary in this driver IC and the driver inputs of other bits are simultaneously switched, a phenomenon called ground bounce that the ground potential of the driver IC rises occurs. Noise may be induced in the stationary bit by the influence of the ground bounce. This is called simultaneous switching noise. When a ground bounce occurs, it takes time for the ground potential to return to 0V,
As a result, the communication delay time has increased. For these reasons, it has been desired to reduce the influence of ground bounce.

As described above, the causes of the disturbance of the signal waveform transmitted through the bus include the influence of the reflected signal and the influence of the ground bounce.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and suppresses the influence of a reflected signal generated on a bus and the influence of ground bounce to thereby reduce a signal transmitted on the bus. It is an object of the present invention to realize a communication device capable of reducing waveform disturbance.

[0011]

SUMMARY OF THE INVENTION The present invention is a communication device having the following configuration.

(1) In a communication device in which a plurality of units are connected to a bus by multi-drop connection and communication is performed between the units via the bus, the line length of the bus is set to a length satisfying the following condition. Communication device. (Transition time of a bus transmission signal) ≤ (time required for a transmission signal to reciprocate between units with the shortest communication distance)

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

(3) Draw a bus for transmitting a plurality of signals,
In a communication device in which a plurality of units are connected on this bus and a plurality of signals are sent out from a driver IC in a transmission circuit of the unit to the bus, the transmission signal is provided in front of the driver IC, and the transmission signal has a bit number of "1". And a decoder provided in the receiving circuit of the unit and for returning the coding signal sent from the transmitting circuit to the original signal, the encoder being configured to code the bit signal having a constant value and then transmitting the signal to the driver IC. A communication device characterized by the above-mentioned.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention. In FIG. 1, the same components as those described above are denoted by the same reference numerals.
In FIG. 1, a plurality of units 21 to 2n are connected to a bus 10 by multi-drop connection. The line length of the bus 10 satisfies the following conditions. (Transition signal transmission time 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 a connection portion of each of the units 22 to 2n. FIG. 2 is a signal waveform diagram at point D. At the point D, the signals reflected by the other units 23 to 2n reach the point D after the reception signal of the unit 22 has transitioned from the high level to the low level. As a result, as shown in FIG. 2, the reflected signals from the units 23 to 2n do not overlap with the transition time of the received signal, and each reflected signal is independent. As a result, the overlapped reflected signals do not exceed the Low level threshold value, and the receiving 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 configured by a wiring pattern formed in a zigzag shape on the substrate 11.

FIG. 4 is a block diagram of another embodiment of the present invention. In FIG. 4, the bus 10 includes a control signal bus 101 and a data bus 102. The unit 21 includes a transmission circuit 21
1 is mounted, and the unit 22 is provided with a receiving circuit 221. Note that both the transmission circuit 211 and the reception circuit 221 may be mounted in one unit.

FIG. 5 is a diagram showing a configuration example of the transmission circuit 211. In FIG. 5, the logic unit 212 outputs a control signal CTL and data D3 to D0. These are bit signals. In the illustrated example, the data D3 to D0 are 4-bit data. The encoder 213 codes the data from the logic unit 212 into a bit signal in which the number of bits of “1” is constant. In the illustrated example, 4-bit data D3 to D0 are coded as 5-bit data DATA4 to DATA0.

FIG. 6 is a diagram showing an example of a coding conversion table. The encoder 213 codes the data D3 to D0 into the data DATA4 to DATA0 according to the conversion table. The number of bits of "1" in data DATA4 to DATA0 is constant at two or three.

Returning to FIG. 5, the driver IC 214 outputs the control signal CTL and the data DATA4 to DATA0 to the bus 10. Here, even if the bit state of the control signal CTL is stationary and the bit states of the data D3 to D0 change simultaneously, the data DATA4 to 0 provided to the driver IC 24 has two or three bits of "1". It is still. As a result, the influence of ground bounce can be suppressed, and noise can be suppressed from being induced in the stationary bit of the control signal CTL.

FIG. 7 is a diagram showing a configuration example of the receiving circuit 221. 7, the receiver 222 receives the control signal CTL and the data DATA4 to DATA0 transmitted via the bus 10. The decoder 223 returns the data DATA4-0 to the original data D3-0. Thus, the transmission data of the transmission circuit 211 is restored. The logic unit 234 processes the control signal CTL and the data D3 to D0.

The number of bits of data before coding, the number of bits of data after coding, and the number of "1" bits of data after coding may be other than the above-mentioned numbers.

[0024]

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

According to the first aspect of the present invention, the line length of the bus is set so that the transition time of the transmission signal of the bus is shorter than the round trip time between the units of the transmission signal. For this reason, in the receiving unit, the reflected signal from another unit arrives after the transition time of the received signal ends. The reflected signal is independent, and malfunction of the receiving unit can be prevented. As a result, it is possible to suppress the influence of the reflected signal generated on the bus.

According to the second aspect of the present invention, since the bus is constituted by the wiring pattern formed in a zigzag pattern on the substrate, the line length of the bus can be extended by effectively using a small space.

According to the third aspect of the present invention, since the transmission data is coded into a bit signal having a constant number of "1" bits before being applied to the driver IC, the influence of ground bounce can be reduced.

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

[Brief description of the drawings]

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

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

FIG. 3 is a configuration diagram of a main part of the embodiment of FIG. 1;

FIG. 4 is a configuration diagram of another embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration example of a transmission circuit according to the embodiment of FIG. 4;

FIG. 6 is a diagram showing an example of a coding conversion table.

FIG. 7 is a diagram illustrating a configuration example of a receiving circuit of the embodiment in FIG. 4;

FIG. 8 is a configuration diagram of a conventional example of a communication device.

FIG. 9 is an equivalent circuit diagram of a bus.

FIG. 10 is a signal waveform diagram of the conventional example of FIG.

[Explanation of symbols]

 10 Bus 21-2n Unit 211 Transmission Circuit 213 Encoder 214 Driver IC 221 Reception Circuit 223 Decoder

Claims (3)

[Claims] 1. A communication device in which a plurality of units are connected to a bus by multi-drop connection and communication is performed between the units via the bus, wherein a line length of the bus is set to a length satisfying the following condition. Communication device. (Transition time of a bus transmission signal) ≤ (time required for a transmission signal to reciprocate between units with the shortest communication distance) 2. The communication device according to claim 1, wherein the bus is formed of a wiring pattern formed in a zigzag pattern on a substrate. 3. A communication device for drawing a bus for transmitting a plurality of signals, connecting a plurality of units on the bus, and transmitting a plurality of signals from a driver IC in a transmission circuit of the unit to the bus, wherein the driver IC Is provided at the preceding stage, and the transmission signal is “1”.
An encoder for coding a bit signal having a fixed number of bits and sending the signal to the driver IC, and a decoder provided in the receiving circuit of the unit and returning the coding signal sent from the transmitting circuit to the original signal. A communication device, comprising: