JP2003046597A - Communication interface circuit, electronic device and bias voltage adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication interface circuit that attains stable communication, where no errors occur when a different bias voltage is generated, depending on a device connected through a serial bus. SOLUTION: A bias generating circuit 11 generates a bias voltage on a pair wire 31, in response to control by a voltage control circuit 13. When, e.g. a bus reset detecting section 12a detects generation of a bus reset, the voltage control circuit 13 controls the bias generating circuit 11 so as to generate a voltage level being a median of voltages of, e.g. the pair wires 31, 32, depending on the detection of the voltage on the pair wires 31, 32 by a voltage comparator circuit 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication interface circuit for performing communication through a serial bus, and a bias voltage adjusting method in this communication interface.

[0002]

2. Description of the Related Art In recent years, with the advent of home digital video devices, it has become necessary to transfer large amounts of information such as moving image data and audio data in real time. As a standard for a serial interface capable of high-speed transfer of such a large amount of data, IEEE (the Instit
ute of Electrical and Electronic Engineers) 139
Four interfaces are known. This IEEE139
The 4 interface can be widely used for connections between home electric appliances such as digital video devices as well as existing peripheral devices for personal computers, LANs, internal buses of personal computers, and the like.

IEEE 1394 serial bus (hereinafter, 1
In the (394 bus), a bias voltage called TP bias is applied to the signal line for transmitting / receiving data. Further, in this 1394 bus, when the bias voltage of the signal line changes more than a predetermined value due to the insertion / removal of a cable or the power ON / OFF, the bus reset is performed and the physical address of each device is automatically assigned.

[0004]

By the way, in the communication through the 1394 bus, the above bias voltage may fluctuate due to a change in system configuration or the like, but the bias voltage is kept within the specified range. For example, since it is possible to perform normal data transfer, it is usually not necessary to adjust the bias voltage, and the device connected to the 1394 bus does not have such a voltage adjusting mechanism. However, since the above-mentioned bias voltage is a common reference voltage for both connected devices to judge signals, in an actual system, when a difference occurs in the voltage level generated in each connected device, A communication error may occur due to the influence of disturbance or the like, and the operation state of the 1394 bus may become unstable.

The present invention has been made in view of the above problems, and when a bias voltage generated by a device connected via a serial bus is different, stable communication can be performed without causing an error. An object is to provide a communication interface circuit.

Further, the present invention is a bias voltage adjusting method in a communication interface circuit, which enables stable communication without error when a bias voltage generated by a device connected through a serial bus is different. Is to provide.

[0007]

According to the present invention, in order to solve the above problems, in a communication interface circuit for performing communication through a serial bus, a bias voltage is applied to a first signal line forming the serial bus. Voltage generating means for generating the voltage, voltage detecting means for detecting the bias voltage in the second signal line constituting the serial bus, and the bias voltage in the first signal line, and the voltage detecting means for detecting the voltage. And a voltage control means for controlling the voltage level generated by the voltage generation means in accordance with the difference between the bias voltages.

In such a communication interface circuit,
The bias voltage on the first and second signal lines forming the serial bus is detected by the voltage detection means,
By the control of the voltage control means, the level of the bias voltage generated by the voltage generation means with respect to the first signal line is controlled according to the difference between the detected voltages by the voltage detection means. The voltage control means, for example, controls the voltage generation means when a bus reset is generated, and, for example, sets the voltage level generated by the voltage generation means to an intermediate value between the bias voltages of the first and second signal lines. Take control.

Further, in the present invention, in the bias voltage adjusting method in the communication interface circuit for performing communication through the serial bus, each bias voltage applied to the two pairs of signal lines included in the serial bus is detected,
A bias voltage adjusting method is provided, wherein a level of the bias voltage generated on one of the signal lines is set to an intermediate value of the detected bias voltages.

In such a bias voltage adjusting method, the bias voltages on the two pairs of signal lines forming the serial bus are detected, and the bias voltage applied to one of the signal lines is detected according to the difference between the detected voltages. The generated voltage is adjusted so that the level becomes the intermediate value of the detected bias voltages.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 2 shows a configuration example of a communication system including electronic equipment including the communication interface circuit of the present invention.

The communication system 100 shown in FIG.
A system for performing communication based on the E1394 standard, which is configured by electronic devices 1 and 2 each including communication interface circuits 10 and 20, and the electronic devices 1 and 2 are connected by a cable 3 configuring a 1394 bus. There is.

The electronic devices 1 and 2 are devices such as personal computers, tuners for digital broadcasting, and digital video tape recorders, and the communication interface circuits 10 and 20 are provided with bias generation circuits 11 and 21, respectively. The cable 3 is a twisted pair cable, and is composed of pair wires 31 and 32. According to the 1394 bus standard, a pair of wires for power supply may be further provided in the cable 3.

In the communication interface circuit 10 provided in the electronic device 1, the pair line 31 is a signal line for strobe transmission called TPA, the pair line 32 is a signal line for data transmission called TPB, and the bias generation circuit. 1
1 applies a bias voltage called TP bias to the pair wire 31. In the communication interface circuit 20 of the electronic device 2, the pair line 32 is for strobe transmission, the pair line 31 is for data transmission, and the bias generation circuit 21 applies a bias voltage to the pair line 32.

Here, in the communication interface circuits 10 and 20, drive circuits (not shown) for signal generation are provided at both ends of the pair lines 31 and 32, respectively. Therefore, the communication interface circuits 10 and 2
Between 0, the bias generation circuit 1 for the pair line 31.
From 1 to 1, the bias voltage generated from the bias generation circuit 21 for the pair line 32 is used as a reference voltage for signal generation.

In the system configuration example of FIG. 2, only the connection between the two electronic devices 1 and 2 is shown.
Each electronic device 1 and 2 may be connected to another electronic device using a 1394 bus.

Next, a configuration example of the communication interface circuit of the present invention will be described. FIG. 1 is a diagram showing a configuration example of the communication interface circuit 10. As shown in Figure 1,
The communication interface circuit 10 includes a bias generation circuit 11 that applies a bias voltage to the pair line 31, a signal processing circuit 12 that performs signal processing for data transmission / reception through the pair lines 31 and 32, and a generated voltage in the bias generation circuit 11. Voltage control circuit 13, which controls the voltage control circuit 13, a reference voltage setting unit 14 which sets a reference value of the generated voltage to the voltage control circuit 13, a voltage on the pair lines 31 and 32, and outputs a signal corresponding to the detected value. It is configured by a voltage comparison circuit 15 that outputs to the control circuit 13.

Pair lines 31 and 32 are connected to the communication interface circuit 10. Pair wire 31 is
These are a pair of signal lines (TPA) for strobe transmission, and the bias generation circuit 11 applies a bias voltage (TP bias) to the pair line 31. The pair lines 32 are a pair of signal lines (TPB) for data transmission, and the communication interface circuit 2 of the electronic device 2 to be communicated with.
At 0, the bias voltage is applied.

The signal processing circuit 12 is provided with a driver circuit (not shown) for generating a signal and a receiver circuit (not shown) for receiving a signal for each of the connected pair lines 31 and 32. The signal processing circuit 12 decodes the packet data received by the receiver circuit to extract the data, outputs the data to a control device (not shown) in the electronic device 1, and encodes the transmission data to packetize the data. Send. Also,
The signal processing circuit 12 includes a bus reset detection unit 12a that outputs a detection signal for the bus reset occurrence to the voltage control circuit 13 when receiving the bus reset signal from the pair line 32.

The signal processing circuit 12 monitors the bias voltage on the pair line 32, and transmits a bus reset signal through the pair line 31 when the voltage exceeds or falls below a predetermined value. Reset detection unit 1
Similarly, at this time, 2a outputs a detection signal for the bus reset occurrence to the voltage control circuit 13. Furthermore, even when the electronic device 1 has a plurality of 1394 bus connection ports and a bus reset signal is transmitted from another electronic device connected by this connection port, the bus reset detection unit 12a does not connect this connection port. The occurrence of a bus reset is detected via.

The voltage control circuit 13 includes a reference voltage setting section 14
Alternatively, the bias generation circuit 11 is controlled so that the bias voltage generated in the bias generation circuit 11 becomes a predetermined value according to the voltage value set by the voltage comparison circuit 15 and the detection signal from the bus reset detection unit 12a. To do. The reference voltage setting unit 14 outputs information for setting the reference value of the generated voltage to the voltage control circuit 13. The voltage comparison circuit 15 detects and compares the voltages of the pair lines 31 and 32, and as described later, the voltage control circuit 13
, The information for setting the intermediate value of each detected voltage is output. Further, the voltage comparison circuit 15 is, for example,
When the bias voltage is not applied to the pair line 32, the voltage control circuit 13 is notified of that fact.

Here, in the pair wires 31 and 32, the average voltage value of the differential signal by the two lead wires provided in each pair wire is set to a predetermined voltage, so that, for example,
A so-called common mode signal such as information about a data transmission rate can be transmitted.
In the IEEE 1394 standard, the allowable range of the reference voltage at the time of sending the common mode signal is 1.665V to 2.
It is specified as 015V.

Therefore, in a device using the IEEE 1394 interface, the bias voltage is normally set to 1.85 V which is an intermediate value of the above-mentioned allowable range, and the reference voltage setting section 14 of the communication interface circuit 10 is also set. ,
Information for setting the voltage generated by the bias generation circuit 11 to 1.85 V is output to the voltage control circuit 13. The bias voltage applied to the pair lines 31 and 32 is usually set to the same voltage value, that is, 1.85V.

However, in an actual system, the voltage applied from the bias generation circuit 11 to the pair line 31
In many cases, there is a difference between the voltage applied to the pair wire 32 in the device to be communicated. Therefore, in the communication interface circuit 10 described above, the pair line 31 is provided by providing the voltage comparison circuit 15 and the voltage control circuit 13.
By detecting the voltage in the pair lines 32 and 32 and changing the voltage generated from the bias generation circuit 11 according to the voltage of the pair line 32 to bring the voltage of the pair line 31 close to the pair line 32, stable communication operation is possible. To do.

The voltage comparison circuit 15 includes pair lines 31 and 3
2 is detected, and when there is a difference in the voltage value, for example, the generated voltage of the bias generation circuit 11 is the pair line 32.
Information for making the voltage the same as the voltage in the voltage control circuit 1
Output to 3. As a result, the voltage control circuit 13 controls the bias generation circuit 11 so that the voltages on the pair lines 31 and 32 become the same.

However, in such voltage control, the electronic device 2 to be communicated, which is connected by the pair lines 31 and 32, is used.
In the case where the function for matching the generated voltage with the bias voltage generated by the device to be communicated is provided in the same manner as described above, the voltage value correcting operation is repeated with each other and the operation is not completed. Therefore, in order to prevent such a malfunction, the voltage comparison circuit 15 compares the voltage generated by the bias generation circuit 11 with the pair lines 31 and 32.
It is preferable to output information such that the intermediate voltage of

Further, for example, the voltage variation on the pair line 32 often occurs when the configuration of the device (node) in the communication network using the 1394 bus changes, and for the pair lines 31 and 32. When the electronic device 2 to be communicated is connected, the generated voltage may be corrected at the time of this connection. Further, when the generated voltage is corrected during the normal communication operation, an erroneous operation for the correction may occur depending on the transmitted / received data.

Therefore, in the communication interface circuit 10 described above, the voltage generated by the bias generation circuit 11 is corrected when the bus reset occurs.
When the voltage control circuit 13 receives the detection signal for the bus reset occurrence from the bus reset detection unit 12 a, the voltage of the pair line 31 is an intermediate voltage between the pair lines 31 and 32 according to the signal supplied from the voltage comparison circuit 15. The bias generation circuit 11 is controlled so that the value becomes a value.

Further, when the bias voltage is not applied to the pair wire 32, that is, when the electronic device 2 is not connected, the voltage control circuit 13 follows the signal supplied from the reference voltage setting section 14 in accordance with the signal supplied from the reference voltage setting section 14. The bias generation circuit 1 so that the voltage on the line 31 becomes 1.85V.
Control 1

Next, FIG. 3 is a flowchart showing the operation of the communication interface circuit 10 described above. At the start of the flowchart of FIG.
In the initial state due to the start of connection to the 394 bus, etc., the voltage control circuit 13
Based on the control of the signal processing circuit 12, the reference voltage setting unit 14
The bias generation circuit 11 is controlled so as to generate the reference voltage of 1.85 V set by the above. Step S3
In 02, the bias generation circuit 11 applies a voltage of 1.85 V to the pair line 31 under the control of the voltage control circuit 13.

In step S303, the bus reset detector 12a of the signal processing circuit 12 monitors the occurrence of the bus reset, and when the occurrence of the bus reset is detected, the process proceeds to step S304. In step S304, the voltage control circuit 13 refers to the signal based on the comparison of the voltages of the pair lines 31 and 32 by the voltage comparison circuit 15.

In step S305, the voltage control circuit 13 detects the presence / absence of a bias voltage on the pair line 32 from the voltage comparison result by the voltage comparison circuit 15, and the pair line 3
It is judged whether or not the other party's electronic device 2 is connected via 1 and 32, and if it is not connected, step S30
Returning to 1, the reference voltage for the pair wire 31, that is, 1.8
The bias generation circuit 11 is controlled so as to apply a voltage of 5 V, and if it is determined that the connection is made, step S
Proceed to 306. Whether or not the electronic device 2 on the other side is connected is detected by the signal processing circuit 12 and the voltage control circuit 1 is detected.
3 may be notified.

In step S306, the voltage control circuit 13 sets the bias voltage to be generated in the bias generation circuit 11 based on the signal from the voltage comparison circuit 15 so as to be an intermediate value between the pair lines 31 and 32. . In step S307, the bias generation circuit 11 applies the voltage of the set intermediate value to the pair line 31, and the pair line 3
The voltage correction of 1 is performed.

With the above processing, in the communication interface circuit 10, the bias voltage applied from the bias generation circuit 11 to the pair line 32 is reduced in accordance with the difference in bias voltage between the pair lines 31 and 32. Therefore, the error caused by the difference in the bias voltage between the devices is prevented for the data transmitted and received through the pair lines 31 and 32, and stable communication can be performed. Further, the bias voltage of the pair line 32 is adjusted to an intermediate value between the detected voltages of the pair lines 31 and 32, so that the same bias voltage adjustment is performed in the electronic device 2 to be connected, This adjustment operation can be performed correctly. Furthermore, by performing such a bias voltage adjustment when a bus reset occurs, it becomes possible to appropriately correspond the applied bias voltage to the communication system using the 1394 bus with the updated node configuration.

[0035]

As described above, in the communication interface circuit of the present invention, the bias voltage on the first and second signal lines forming the serial bus is detected by the voltage detection means, and the voltage control means is controlled. Thus, the level of the bias voltage generated by the voltage generating means with respect to the first signal line is controlled according to the difference in the voltage detected by the voltage detecting means. Therefore, the difference between the bias voltages on the first and second signal lines is reduced, a communication error caused by this difference is prevented, and stable communication can be performed.

Further, in the bias voltage adjusting method of the present invention, each bias voltage in the two pairs of signal lines forming the serial bus is detected, and applied to one of the signal lines in accordance with the difference between the detected voltages. The bias voltage level is
The generated voltage is adjusted so as to have an intermediate value of the detected bias voltages. Therefore, the difference between the bias voltages on the first and second signal lines is reduced, a communication error caused by this difference is prevented, and stable communication can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a communication interface circuit of the present invention.

FIG. 2 is a diagram showing a configuration example of a communication system configured by an electronic device including the communication interface circuit of the present invention.

FIG. 3 is a flowchart showing an operation in the communication interface circuit of the present invention.

[Explanation of symbols]

1, 2 ... Electronic equipment, 3 ... Cable, 10 ... Communication interface circuit, 11 ... Bias generating circuit, 12 ...
... signal processing circuit, 12a ... bus reset detection unit, 13
...... Voltage control circuit 14 ...... Reference voltage setting unit 15 ......
Voltage comparison circuit, 20 ... Communication interface circuit, 21
...... Bias generator circuit, 31, 32 …… Pair wire, 100
……Communications system

Claims (7)

[Claims] 1. A communication interface circuit for performing communication via a serial bus, comprising: voltage generating means for generating a bias voltage for a first signal line forming the serial bus; and second voltage forming the serial bus. Voltage detecting means for detecting the bias voltage on the signal line and the bias voltage on the first signal line, and the voltage generating means according to the difference between the bias voltages detected by the voltage detecting means. And a voltage control means for controlling the voltage level generated by the communication interface circuit. 2. A bus reset detecting means for detecting the occurrence of a bus reset through the second signal line, wherein the voltage control means detects the occurrence of the bus reset by the bus reset detecting means. The communication interface circuit according to claim 1, further comprising: controlling the voltage generating means. 3. The voltage control means controls the voltage generation means so that the generated voltage level becomes an intermediate value of bias voltages in the first and second signal lines. The communication interface circuit according to claim 1. 4. The voltage control means controls the voltage generation means so that the generated voltage level becomes 1.85 V when the bias voltage on the second signal line is at a ground potential. The communication interface circuit according to claim 1. 5. The communication interface circuit according to claim 1, wherein the serial bus complies with the IEEE 1394 standard. 6. An electronic device comprising the communication interface circuit according to claim 1. 7. A bias voltage adjusting method in a communication interface circuit for performing communication through a serial bus, wherein each bias voltage applied to two pairs of signal lines included in the serial bus is detected, and one of the signal lines is detected. The bias voltage level generated for the bias voltage is set to an intermediate value of the detected bias voltages.