JP2009253498A - Communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication apparatus for reducing ringing on a transmission line in signal transition, while keeping communication performance. <P>SOLUTION: The communication apparatus for communicating with another apparatus via the transmission line 12<SB>1</SB>includes: a terminating part 20 for suppressing the ringing in the transmission line 12<SB>1</SB>; a communication end detecting part 22 for detecting the end of the communication with another apparatus; and a terminal end driving part 24 for connecting the terminal end 20 to the transmission line 12<SB>1</SB>for a prescribed time from the end of the communication when the communication end detecting part 22 detects the end of the communication. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a communication apparatus including a termination unit for suppressing ringing generated in a transmission line.

  In a communication system that communicates between devices via a transmission line, ringing occurs on the transmission line when the signal transitions from high to low or from low to high due to impedance mismatch between the devices and the transmission line. There are things to do. For example, ringing generated on the transmission line in the transmission side device at the time of bus-off in a communication system such as CAN (Controller Area Network) and FlexRay (registered trademark) is received as a reception signal in the reception side device and malfunctions depending on the case. It is thought to cause. Note that both CAN and FlexRay employ a multiplex communication system, but FlexRay differs from CAN in that it employs a time division multiplex communication system in which a time trigger protocol is defined.

  In order to avoid such a problem, it is conventionally known to provide a termination circuit in a device on the reception side or transmission side (see, for example, Japanese Patent No. 3821982). The termination circuit is disposed near the input unit that receives data in the receiving side device, and near the output unit that transmits data in the transmitting side device, and is inserted in parallel between the transmission line and the ground. .

Also, a method is known in which a specified value (for example, 244 ns when the data rate is 5 Mbps or 400 ns when the data rate is 2.5 Mbps) is set in a period in which ringing occurs, and that period is handled as an unused area of communication. It has been.
Japanese Patent No. 3821982

  However, the method using the termination circuit has a problem in that the data signal rises and falls due to the influence of the termination circuit during normal operation in which ringing does not occur. In addition, in the method in which the period during which ringing occurs is treated as an unused area for communication, the communication efficiency decreases due to the existence of an unused area for communication, the restriction on the degree of routing freedom due to strict specified values, and normal communication. There are problems such as the need for additional measures to wake up.

  In view of the above problems, an object of the present invention is to provide a communication device that can reduce ringing that occurs on a transmission line during signal transition while maintaining communication performance.

In order to achieve the above object, a communication device of the present invention is a communication device that communicates with another device via a transmission line,
A termination portion for suppressing ringing generated in the transmission path;
A communication end detection unit for detecting the end of communication with the other device;
When the communication end detection unit detects the end of communication, the communication end detection unit includes a termination driving unit that connects the termination unit to the transmission path for a predetermined time from the end of communication.

  As a result, it is possible to provide a communication device that can reduce ringing that occurs on the transmission path during signal transition while maintaining communication performance. By inserting a termination unit that suppresses ringing that occurs in the transmission path only during a predetermined time during which ringing occurs from the time of signal transition, that is, from the end of communication, the communication waveform is not dulled during normal operation. . In addition, since it is not necessary to treat the period in which ringing occurs as an unused area of communication, problems such as a reduction in communication efficiency, restrictions on the degree of freedom of routing, and the need for additional measures do not occur.

  As an embodiment, in the communication device of the present invention, the transmission path is a differential signal transmission path, and the first transmission path that transmits the first signal and the phase is inverted with respect to the first signal. A second transmission path for transmitting the second signal, and the termination unit is connected between the first transmission path and the second transmission path by the termination driving unit. The

  As a result, the component constant is reduced as compared with the case where the terminal portions are provided in the respective transmission lines, so that cost reduction and space securing can be achieved.

  As one embodiment, in the communication device according to the present invention, the communication end detection unit delays a transmission enable signal indicating that data transmission to the other device is possible by the predetermined time; Inversion means for inverting the transmission enable signal delayed by the predetermined time by the delay means, the transmission enable signal delayed and inverted by the delay means and the inversion means, and the original transmission enable signal Logical operation means for calculating.

  As another embodiment, the communication device of the present invention can include a signal switching detection unit that detects switching between high and low of a data signal transmitted to the other device, instead of the communication end detection unit. . The signal switching detection unit includes logical operation means for calculating a logical product of a transmission enable signal indicating that data transmission to the other device is possible and the data signal transmitted to the other device. . At this time, the termination driving unit connects the termination unit to the transmission line when the signal switching detection unit detects switching of the data signal from low to high.

  As a result, not only at the end of communication, but also at the time of signal transition during data communication such as when the CAN system shifts from dominant to recessive, it is possible to suppress the ringing that occurs in the transmission path by inserting a termination unit. It becomes possible.

  In this embodiment, when the communication device transmits identification data for identifying the communication device to the other device at the start of communication with the other device, the transmission enable signal is preferably After the identification data is transmitted, it indicates that the data can actually be transmitted to the other device.

  Thereby, in the communication system in which arbitration is performed, the termination is not inserted during the period in which the identification data is transmitted, so that arbitration is not hindered.

  In any of the embodiments, in the communication device of the present invention, the termination may be configured by a series circuit of a resistor and a capacitor. Alternatively, the termination unit may be configured to directly connect the first transmission line and the second transmission line.

  According to the present invention, it is possible to provide a communication device capable of reducing ringing that occurs on a transmission line during signal transition while maintaining communication performance.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 shows a communication transmission system in which a communication device 10 according to the present invention is connected to another device 14 via a transmission line 12. The communication device 10 includes a transmitter 110 that transmits a data signal to another device 14 via the transmission line 12, and a ringing suppression unit 120 that suppresses occurrence of ringing on the transmission line. The ringing suppression unit 120 is connected to the transmission line 12 near the output unit of the communication apparatus 10 to which the data signal transmitted from the transmitter 110 is output.

  Next, how the ringing generated on the transmission line can be suppressed by the communication device 10 according to the present invention will be described with a specific example.

Figure 2 is a block diagram showing an example of a ringing suppression portion 120 ₁ of the arrangement according to the present embodiment. Ringing suppression unit 120 ₁ includes a suppressing terminal portion 20 ringing that occurs in the transmission line 12 _1, the communication end detection unit 22 that detects the end of communication with other devices (device 14 in FIG. 1), communication end When the detection unit 22 detects the end of communication, between the end of the communication for a predetermined time, and a termination driver 24 which connects the terminal portion 20 to the transmission line 12 _1.

In the example shown in FIG. 2, the transmission line 12 ₁ is a differential signal transmission path, the first transmission line and the BP of transmitting the first signal, the phase with respect to the first signal is inverted And a second transmission line BM for transmitting the second signal. The termination unit 20 is configured to be connected between the first transmission path BP and the second transmission path BM by the termination driving unit 24.

  The communication end detection unit 22 delays a transmission enable signal TxEN indicating that data transmission to another device is possible by a predetermined time, and a transmission enable signal dEN delayed by a predetermined time by the delay unit 210. An inversion unit 220 that inverts, and a logical operation unit 230 that calculates a logical product of the transmission enable signal invEN delayed and inverted by the inversion unit 220 and the original transmission enable signal TxEN.

FIG. 3 is a timing chart relating to signals of the respective units of the communication end detection unit 22. The transmission enable signal TxEN is output from the transmitter 110 and indicates that the transmitter 110 can perform data transmission. While the data signal to another device 14 via the transmission path 12 ₁ from the communication apparatus 10 by transmitter 110 is transmitted, transmission enable signal TxEN is low (i.e., "0"). The signal dEN is a transmission enable signal delayed by a predetermined time t by the delay unit 210. The signal invEN is a transmission enable signal delayed and inverted by the delay unit 210 and the inversion unit 220. The signal Out is a signal representing a logical product of the transmission enable signal invEN delayed and inverted and the original transmission enable signal TxEN, and is output from the communication end detection unit 22 as a detection result.

  At the start of the bus-off period, that is, when the transmitter 110 finishes data transmission, the transmission enable signal TxEN transitions from low to high (ie, “1”). At this time, the delayed and inverted transmission enable signal invEN remains high. Thereafter, after a predetermined time t has elapsed, the signal invEN transitions from high to low. Accordingly, the signal Out is high from the start of the bus off period until the predetermined time t elapses.

Terminating driving unit 24, in response to this signal Out, at the start of the bus off period (i.e., the end of the communication with other devices) connected from a predetermined time t, the terminal portion 20 to the transmission line 12 ₁ be able to.

  In the present embodiment, the predetermined time t is a period in which ringing occurs when the bus is off, and is determined by experiments assuming the worst case. For example, in the case of CAN with a transmission rate of 500 kbps, the ringing occurrence period is generally about 600 nsec.

Figure 4 represents an example of a circuit constituting a ringing suppression portion 120 ₁ represented in FIG. The termination unit 20 has a series circuit of a resistor R1 and a capacitor C1. The termination driver 24 includes an npn transistor Tr and a relay switch SW. The transistor Tr has a collector connected to a DC power supply VDD (for example, 5 V) via the switch SW, an emitter connected to the ground, and a base connected to the output of the logic operation unit 230. The delay unit 210 includes a resistor R2 connected in series between the transmission enable signal input unit and the inverting unit 220, and a capacitor C2 connected in parallel between the input of the inverting unit 220 and the ground. The inversion unit 220 includes an inverter that can invert a signal. The logical operation unit 230 includes an AND circuit that outputs a logical product of two input signals.

  The transmission enable signal TxEN is input to each of the delay unit 210 and the logic operation unit 230. The delay unit 210 is a delay circuit including a resistor R2 and a capacitor C2, and delays the transmission enable signal according to a time constant determined by the constants of the resistor R2 and the capacitor C2. Next, the inversion unit 220 inverts the transmission enable signal delayed by the delay unit 210. The logical operation unit 230 outputs a logical product of the transmission enable signal delayed and inverted by the delay unit 210 and the inversion unit 220 and the original transmission enable signal TxEN.

  The output of the logic operation unit 230 is input to the base of the transistor Tr of the termination drive unit 24. In this embodiment, as shown in FIG. 3, the logical operation unit 230 outputs a signal Out = “1” until a predetermined time t elapses after the end of communication with another device. Accordingly, the transistor Tr is turned on during this period. When the transistor Tr is turned on, the relay switch SW is turned on, and the termination unit 20 is inserted between the first transmission path BP and the second transmission path BM. Thereby, at the time of signal transition, in the present embodiment, it is possible to suppress ringing that occurs on the transmission line during a predetermined time t from the end of communication. Since the termination unit 20 is inserted only during a period in which the occurrence of ringing is desired to be suppressed, the communication waveform is not dulled during normal operation.

  In addition, in this way, by using a hardware configuration to prevent the occurrence of ringing, it is not necessary to treat the period in which ringing occurs as an unused area of communication, so the communication efficiency decreases, the degree of freedom of routing, And there is no need for additional measures.

  Next, using CAN as an example, an embodiment will be described in which, for example, a termination unit for suppressing the occurrence of ringing is connected to a transmission line when shifting from dominant to recessive during data communication.

Figure 5 is a block diagram showing an example of the configuration ringing suppression section ₁₂₀₂ according to this embodiment. Transmission line 12 ₂ for use in CAN system is a differential signal transmission line, a first transmission line CAN_H for transmitting a first signal, the second phase with respect to the first signal is inverted 2 And a second transmission path CAN_L for transmitting the above signal. Ringing suppression unit 120 ₂ has a terminal portion 20 and the end drive unit 24 similarly to the ringing circuit 120 ₁ according to Example 1, in place of the communication end detection unit 22, to another device (apparatus 14 of FIG. 1) A signal switching detection unit 26 that detects switching between high and low of the data signal TxD to be transmitted is included. The termination drive unit 24 connects the termination unit 20 between the first transmission path CAN_H and the second transmission path CAN_L when the signal switching detection unit 26 detects the switching of the data signal from low to high. The signal switching detection unit 26 includes a logical operation unit 240 that calculates a logical product of a transmission enable signal DTxEN indicating that data transmission to another device is possible and a data signal TxD transmitted to the other device. .

  FIG. 6 is a timing chart regarding the transmission enable signal DTxEN and the data signal TxD input to the signal switching detection unit 26 and the output signal Out. The transmission enable signal DTxEN is output from the transmitter 110 (FIG. 1), and indicates that the transmitter 110 can perform data transmission. The transmission enable signal DTxEN transitions from low to high at the timing when the transmitter 110 transmits the identification data ID for identifying the device itself, and transmits the actual data to another device so as not to prevent the arbitration from being performed. Then, after data transmission is completed, it goes low again. The data signal TxD is output from the transmitter 110 and indicates data to be transmitted to another device in binary numbers of “0” (low) and “1” (high). The signal Out is a signal that represents a logical product of the transmission enable signal DTxEN and the data signal TxD, and is output from the signal switching detection unit 26 as a detection result.

  At the start of communication, transmitter 110 transmits its own identification data ID for arbitration. Thereafter, when the arbitration is properly completed, the transmitter 110 transmits the actual data to another device. At this time, the transmission enable signal DTxEN transitions from low to high. Therefore, until the data transmission is completed, the signal Out is high when the transmission data TxD = "1", and is low when the transmission data TxD = "0".

Terminating driving unit 24 may be connected in response to this signal Out, the terminal portion 20 to the transmission path 12 ₂ when the transmission data TxD = "1".

  Note that the last part of the transmission data TxD corresponding to the ACK field of the CAN frame is actually a signal transmitted from another device for data reception confirmation. However, in this period as well, ringing is suppressed by using the termination unit 20 in the communication device 10 that is actually the receiving side. This is because an ACK signal may be transmitted from a plurality of devices. In other words, when ringing is suppressed in each device that transmits the ACK signal at the time of transmitting the ACK signal, a plurality of termination units are connected to the transmission line at a time, and the bus capacity is reduced. Because it will increase.

Figure 7 represents an example of a circuit constituting a ringing suppression portion 120 ₂ represented in FIG. The termination unit 20 has a series circuit of a resistor R1 and a capacitor C1. The termination driver 24 includes an npn transistor Tr and a relay switch SW. The transistor Tr has a collector connected to a DC power supply VDD (for example, 5 V) via a switch SW, an emitter connected to the ground, and a base connected to the output of the logic operation unit 240. The logical operation unit 240 has an AND circuit that outputs a logical product of two input signals.

  The transmission enable signal DTxEN is input to one input terminal of the logic operation unit 240. The data signal TxD is input to the other input terminal of the logic operation unit 240. The logical operation unit 240 outputs a logical product of the transmission enable signal DTxEN and the transmission data TxD.

  The output of the logical operation unit 240 is input to the base of the transistor Tr of the termination driving unit 24. In this embodiment, as shown in FIG. 6, the logical operation unit 230 outputs the signal Out = “1” when the transmission data TxD = “1” until the data transmission is completed. Therefore, the transistor Tr is turned on when the transmission data TxD = “1”. When the transistor Tr is turned on, the relay switch SW is turned on, and the termination unit 20 is inserted between the first transmission path CAN_H and the second transmission path CAN_L. As a result, at the time of signal transition, in this embodiment, it is possible to suppress ringing that occurs on the transmission line when the transmission data signal is switched from low to high. Since the termination | terminus part 20 is inserted only in the period which wants to suppress generation | occurrence | production of ringing, a communication waveform is not blunted in other periods (for example, the period when arbitration is implemented).

  Further, as in the first embodiment, by using a hardware configuration to prevent the occurrence of ringing, it is not necessary to treat the period in which ringing occurs as an unused area of communication, resulting in a reduction in communication efficiency and routing flexibility. There will be no problems such as restrictions and necessity of additional measures.

[Modification]
Here, some modifications to the above-described embodiment will be described.

  In the first modification, the termination portion may be configured to directly connect the first transmission path and the second transmission path instead of the series circuit of the resistor and the capacitor. When the ringing generated in each transmission path is symmetric, that is, in the case of the same amplitude and opposite phase, an effect of canceling the ringing can be expected by directly connecting the two transmission paths.

  In the second modified example, the termination portion may be connected between each transmission line and the ground instead of being inserted between the two differential signal transmission lines. In this case, since one termination unit must be prepared for each transmission line, it is disadvantageous in terms of cost and space compared to the above embodiment, but the influence of one transmission line directly affects the other transmission line. This is advantageous in that it is not.

  In the third modification, the switch used in the terminal drive unit may be another switching element such as a transistor or FET instead of the relay switch. It is preferable to select an appropriate switching element depending on the situation where ringing suppression is required.

  Although the best mode for carrying out the invention has been described above, the present invention is not limited to the embodiment described in the best mode. Modifications can be made without departing from the spirit of the present invention.

  For example, although the embodiment of the present invention has been specifically described with respect to CAN in the second embodiment, it can be applied to other communication systems such as FlexRay (registered trademark).

1 represents a communication transmission system in which a communication device according to the present invention is connected to another device via a transmission line. 3 is a block diagram illustrating an example of a configuration of a ringing suppression unit according to Embodiment 1. FIG. FIG. 3 is a timing chart relating to signals of respective units of the communication end detection unit illustrated in FIG. 2. 3 shows an example of a circuit constituting the ringing suppression unit shown in FIG. FIG. 10 is a block diagram illustrating an example of a configuration of a ringing suppression unit according to a second embodiment. FIG. 6 is a timing diagram regarding an input signal and an output signal of the signal switching detection unit illustrated in FIG. 5. 6 illustrates an example of a circuit constituting the ringing suppression unit illustrated in FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Communication apparatus 12 Transmission path 110 Transmitter 120 Ringing suppression part 20 Termination part 22 Communication end detection part 24 Termination drive part 26 Signal switching detection part 210 Delay part 220 Inversion part 230,240 Logic operation part

Claims (6)

A communication device that communicates with other devices via a transmission line,
A termination portion for suppressing ringing generated in the transmission path;
A communication end detection unit for detecting the end of communication with the other device;
When the communication end detection unit detects the end of communication, the communication device includes a termination driving unit that connects the termination unit to the transmission path for a predetermined time from the end of communication. The transmission path is a differential signal transmission path, a first transmission path for transmitting a first signal, and a second signal for transmitting a second signal whose phase is inverted with respect to the first signal. Transmission line,
The communication device according to claim 1, wherein the termination unit is connected between the first transmission path and the second transmission path by the termination driving unit. The communication end detection unit
Delay means for delaying the transmission enable signal indicating that data transmission to the other device is possible by the predetermined time;
Inverting means for inverting the transmission enable signal delayed by the predetermined time by the delay means;
The communication apparatus according to claim 1, further comprising: a logical operation unit that calculates a logical product of the transmission enable signal delayed and inverted by the delay unit and the inversion unit, and the original transmission enable signal. In place of the communication end detection unit, a signal switching detection unit that detects switching between high and low of a data signal transmitted to the other device,
The signal switching detection unit
Logical operation means for calculating a logical product of a transmission enable signal indicating that data transmission to the other device is possible and the data signal transmitted to the other device;
The communication apparatus according to claim 1, wherein the termination driving unit connects the termination unit to the transmission line when the signal switching detection unit detects switching of the data signal from low to high. When the communication device transmits identification data for identifying the communication device to the other device at the start of communication with the other device,
The communication device according to claim 4, wherein the transmission enable signal indicates that data transmission to the other device is actually possible after the identification data is transmitted.   The communication device according to claim 1, wherein the termination unit is a series circuit of a resistor and a capacitor.

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