JPH0897863A - Serial communication equipment - Google Patents

Abstract

PURPOSE: To obtain a serial communication equipment with a small circuit scale, whereby serial communication following plural interface standards is executed. CONSTITUTION: A voltage +12V and the voltage -12V are applied to a differential transmission circuit 2 by switches 5 and 6 at the time of transmission in RS232C communication and the voltage +5V and ground potential 0V are applied to the differential transmission circuit 2 by the switches 5 and 6 at the time of transmission in RS422 communication. A clipping circuit 4 is connected to the input terminals I30 and I31 of a differential reception circuit 3. At the time of reception in RS232C communication, a reception signal restricted by the clipping circuit 4 is given to one of the input terminals I30 of the circuit 3 and the other input terminal is pulled-up to +2.5V. At the time of reception in RS422 communication, a differential signal is given to the input terminals I30 and I31 of the differential reception circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a serial communication device for transmitting / receiving serial data.

[0002]

2. Description of the Related Art In serial communication complying with an unbalanced interface standard such as RS232C, one signal line is provided for a ground line. For example, a voltage of +5 to +15 V is applied to the signal line corresponding to data "1". Are applied, and voltages of -5 to -15V are applied to the signal line corresponding to the data "0".

On the other hand, in serial communication complying with a balanced interface standard such as RS422, two complementary signal lines are provided with respect to the ground line, and differential signals are given to these signal lines. For example, a voltage + 5V is applied to one signal line corresponding to data "1", a voltage 0V is applied to the other signal line, and a voltage 0V is applied to one signal line corresponding to data "0". And the voltage + 5V is applied to the other signal line. In this case, the voltage difference between the two signal lines is ± 5V.

Hereinafter, serial communication conforming to the RS232C interface standard will be referred to as RS232C communication, and RS42
Serial communication conforming to the 2-interface standard RS422
Called communication. A signal complying with the RS232C interface standard is called an RS232C signal, and a signal complying with the RS422 interface standard is called an RS422 signal.

FIG. 7 shows RS232C communication and RS42.
It is a block diagram which shows an example of the conventional serial communication apparatus which can perform 2 communication. The serial communication device of FIG. 7 includes a serial communication control circuit 11, an RS232C transmission circuit 12, and an RS4.
22 differential transmission circuit 13, RS232C reception circuit 14, R
The S422 differential receiving circuit 15 and the switch 16 are included.

At the time of transmission in RS232C communication, R
The S232C transmission circuit 12 uses the serial communication control circuit 11
The transmission data SD given from RS232C signal SD
It is converted to 2 and output from the output terminal O11. RS422
At the time of transmission in communication, the RS422 differential transmission circuit 13
Converts the transmission data SD given from the serial communication control circuit 11 into RS422 signals SD4A and SD4B and outputs them from output terminals O12 and O13, respectively. Here, the RS422 signal SD4B is the RS422 signal SD4.
It is an inverted signal of A.

During reception in RS232C communication, the movable contact a of the switch 16 is switched to the contact b side. The RS232C reception circuit 14 inputs the RS232C signal RD2 transmitted to the input terminal I11, converts the RS232C signal RD2 into reception data RD, and supplies the reception data RD to the serial communication control circuit 11 via the switch 16. When receiving in RS422 communication, the movable contact a of the switch 16 is switched to the contact c side. The RS422 differential receiving circuit 15 receives the RS422 signal R transmitted to the input terminals I12 and I13.
D4A and RD4B are input, they are converted into reception data RD, and the serial communication control circuit 1 is provided via the switch 16.
Give to one. Here, RS422 signal RD4B is RS
This is an inverted signal of the 422 signal RD4A.

FIG. 8 shows RS232C communication and RS42.
It is a block diagram which shows the other example of the conventional serial communication apparatus which can perform 2 communication. The serial communication device of FIG. 8 is similar to the serial communication device of FIG.
1, RS232C transmitting circuit 12, RS422 differential transmitting circuit 13, RS232C receiving circuit 14, RS422 differential receiving circuit 15, and switch 16, and further includes switches 17 and 18. The switches 16, 17, and 18 are interlocked.

At the time of transmission in RS232C communication, the movable contact a of the switches 16, 17, 18 is switched to the contact b side. The RS232C transmission circuit 12 transmits the transmission data SD supplied from the serial communication control circuit 11 to RS.
It is converted into a 232C signal SD2 and output from the output terminal O14. When transmitting in RS422 communication, switch 1
The movable contacts a of 6, 17, and 18 are switched to the contact c side. The RS422 differential transmission circuit 13 converts the transmission data SD given from the serial communication control circuit 11 into RS422.
Signals SD4A and SD4B are converted to output terminals O
Output from 14 and O15.

At the time of reception in RS232C communication, the movable contacts a of the switches 16, 17, and 18 are switched to the contact b side. The RS232C reception circuit 14 inputs the RS232C signal RD2 transmitted to the input terminal I14, converts the RS232C signal RD2 into reception data RD, and supplies the reception data RD to the serial communication control circuit 11. At the time of reception in RS422 communication, the movable contacts a of the switches 16, 17, and 18 are switched to the contact c side. The RS422 differential receiving circuit 15
The RS422 signals RD4A and RD4B transmitted to the input terminals I14 and I15 are input, and they are received data R
It is converted to D and given to the serial communication control circuit 11.

9A and 9B show RS232C.
3 is a circuit diagram showing a configuration of a transmission circuit 12. FIG. FIG. 9 (a)
As shown in FIG.
It consists of 20. As shown in FIG. 9B, the buffer 1
20 is two bipolar transistors 121, 122
And two resistors 123 and 124.

For example, a voltage + 12V (maximum + 15V) is applied to the positive power supply terminal P120 of the buffer 120, and a voltage -12V (maximum -15V) is applied to the negative power supply terminal P121.
V) is given. Input terminal I120 of the buffer 120
To the RS232C signal SD2 of + 12V or -12V from the output terminal O120.
Is output.

FIG. 10 is a circuit diagram showing the structure of the RS422 differential transmission circuit 13. As shown in FIG.
The 2C differential transmission circuit 13 includes a buffer 130 and an inverter 131.

For example, a voltage + 5V is applied to the power supply terminal P130 of the buffer 130, and a ground potential 0V is applied to the ground terminal P131 of the inverter 131. Buffer 1
30 and the common input terminal I130 of the inverter 131
To the output terminals O130 and O1
31 to RS422 signals SD4A and SD4 complementary to each other
B is output.

FIGS. 11A and 11B show RS232.
6 is a circuit diagram showing a configuration of a C reception circuit 14. FIG. As shown in FIG. 11A, the RS232C receiving circuit 14 includes a buffer 140. As shown in FIG. 11B, the buffer 140 includes a bipolar transistor 141, resistors 142, 143, 144 and a diode 145.

For example, a voltage + 12V (maximum 15V) is applied to the positive power supply terminal P140 of the buffer 140, and a voltage -12V (maximum -15V) is applied to the negative power supply terminal P141.
Is given. For example, the RS232C signal RD2 of + 12V or -12V is input to the input terminal I140 of the buffer 140.
And the received data RD is output from the output terminal O140.

FIG. 12 is a circuit diagram showing the structure of the RS422 differential receiving circuit 15. As shown in FIG.
The two-differential receiving circuit 15 includes a differential amplifier 150. For example, the voltage + 5V is applied to the power supply terminal P150 of the differential amplifier 150.
And a ground potential 0V is applied to the ground terminal P151. The RS422 signal R complementary to each other is input to the input terminal I150 and the inverting input terminal I151 of the differential amplifier 150.
D4A and RD4B are given, and the reception data RD is output from the output terminal O150.

[0018]

As described above, in the serial communication device of FIG. 7, the RS232C transmitter circuit 12 and the RS232C receiver circuit 1 are used for RS232C communication.
4, an output terminal O11 and an input terminal I11 are provided, and RS
RS422 differential transmission circuit for RS422 communication, RS42
2 The differential receiving circuit 15, the output terminals O12 and O13, and the input terminals I12 and I13 are provided, and the RS is switched by the switch 16.
232C communication and RS422 communication are switched.

On the other hand, in the serial communication device of FIG. 8, the RS232C transmission circuit 1 is used for RS232C communication.
3 and RS232C receiver circuit 14 are provided, and RS422
RS422 differential transmission circuit 13 and RS4 for communication
22 a differential receiving circuit 15 is provided and a common output terminal O1
4, O15 and common input terminals I14, I15 are provided, and the switches 16, 17, 18 switch between RS232C communication and RS422 communication.

As described above, in the conventional serial communication device, circuits for transmitting and receiving RS232C communication and RS422 communication are required respectively, so that the circuit scale becomes large, hindering downsizing, and the product cost. Becomes higher. Further, in the serial communication device of FIG.
The number of output terminals and input terminals is smaller than that of the serial communication device of FIG. 7, but a switch with multiple contacts is required.

An object of the present invention is to provide a serial communication device capable of performing serial communication complying with a plurality of interface standards with a small circuit scale.

[0022]

A serial communication apparatus according to the present invention converts serial transmission data into a differential signal composed of complementary first and second signals, and outputs both the first and second signals. Or differential transmission means for transmitting one of them serially, differential reception means for receiving a differential signal or a single signal serially, and converting the differential signal or single signal and a constant potential into serial reception data, Power supply voltage switching means for switching the power supply voltage supplied to the differential transmission means.

In particular, it is preferable to further include voltage limiting means for limiting the voltage of the received differential signal or single signal within a predetermined range.

[0024]

In the serial communication device according to the present invention, the power supply voltage supplied to the differential transmission means is switched according to the interface standard. During transmission in communication according to the balanced interface standard, serial transmission data is converted by the differential transmission means into first and second signals complementary to each other according to the balanced interface standard, and these signals are serially transmitted. During transmission in communication according to the unbalanced interface standard, the differential transmission means converts the serial transmission signal into first and second signals having a voltage according to the unbalanced interface standard, and one of them is transmitted serially.

At the time of reception in the communication conforming to the balanced interface standard, a differential signal having a voltage difference conforming to the balanced interface standard is serially received, and the differential signal is converted into serial reception data by the differential receiving means. When receiving in communication according to the unbalanced interface standard, a single signal having a voltage according to the unbalanced interface standard is serially received, and the single signal and a constant potential are converted into serial reception data by the differential receiving means. .

In particular, when a voltage limiting means for limiting the voltage of the received differential signal or single signal within a predetermined range is further provided, one of the received signals complying with a plurality of interface standards is differential. The breakdown of the differential receiving means is prevented when the allowable voltage of the receiving means is exceeded.

[0027]

1 is a block diagram showing the configuration of a serial communication apparatus according to an embodiment of the present invention. This serial communication device can perform RS232C communication and RS422 communication.

The serial communication device of FIG. 1 includes a serial communication control circuit 1, a differential transmission circuit 2, a differential reception circuit 3, a clipping circuit 4, switches 5, 6, current limiting resistors 7, 8 and a pull-up resistor 9. Including. The switches 5 and 6 are interlocked.

The power supply terminal P1 is supplied with a voltage + 12V, the power supply terminal P2 is supplied with a voltage + 5V, and the power supply terminal P3 is supplied with a voltage -12V. A ground potential 0V is applied to the ground terminal P4. The differential receiving circuit 3 is always supplied with a voltage + 5V applied to the power supply terminal P2 and a ground potential 0V applied to the ground terminal P4. In the example of FIG. 1, the switches 5 and 6 form a power supply voltage switching circuit.

During RS232C communication, switches 5 and 6
The movable contact a of is switched to the contact b side. As a result, the voltage + 12V applied to the power supply terminal P1 and the voltage -12V applied to the power supply terminal P3 are supplied to the differential transmission circuit 2.

At the time of transmission, the differential transmission circuit 2 transmits the transmission data SD supplied from the serial communication control circuit 1 to RS2.
The 32C signal SD2 is converted and output from the output terminal O1. RS2 transmitted to the input terminal I1 during reception
The 32C signal RD2 is input to the input terminal I30 of the differential receiving circuit 3 via the current limiting resistor 7. At this time, the voltage of the input terminal I2 is fixed to + 2.5V by the pull-up resistor 9. Further, the clipping circuit 4 limits the voltage of the input terminals I30 and I31 of the differential receiving circuit 3 within the range of 0V to + 5V. The differential receiving circuit 3 receives the input R
The S232C signal RD2 is converted into the reception data RD and given to the serial communication control circuit 1.

During RS422 communication, the movable contact a of the switches 5 and 6 is switched to the contact c side. As a result, the voltage + 5V applied to the power supply terminal P2 and the ground potential 0V applied to the ground terminal P4 are supplied to the differential transmission circuit 2.

At the time of transmission, the differential transmission circuit 2 transmits the transmission data SD supplied from the serial communication control circuit 1 to RS4.
22 signals SD4A, SD4B converted to output terminals O1,
Output from O2 respectively.

At the time of reception, RS422 signals RD4A and RD4B transmitted to the input terminals I1 and I2 are input to the input terminals I30 and I31 of the differential receiving circuit 3 via the current limiting resistors 7 and 8, respectively. The differential reception circuit 3 converts the input RS422 signals RD4A, RD4B into reception data RD and gives it to the serial communication control circuit 1.

FIG. 2 is a block diagram showing the configuration of the serial communication control circuit 1. As shown in FIG. 2, the serial communication control circuit 1 includes a CPU (Central Processing Unit) 10 and a serial communication control IC 11.

The CPU 10 gives parallel transmission data to the serial communication control IC 11 at the time of transmission, and receives parallel reception data from the serial communication control IC 11 at the time of reception. The serial communication control IC 11 sends the data to the CPU 1 when transmitting.
The parallel transmission data given from 0 is converted into the serial transmission data SD and output, and at the time of reception, the input serial reception data RD is converted into the parallel reception data and C
Give to PU10.

FIG. 3 is a circuit diagram showing the configuration of the differential transmission circuit 2. As shown in FIG. 3, the differential transmission circuit 2 includes a CMO.
The buffer 20 is composed of an S circuit and an inverter 21. The output terminal O22 is grounded.

During RS232C communication, a voltage + 12V is applied to the power supply terminal P20 of the buffer 20, and a voltage -12V is applied to the power supply terminal P21 of the inverter 21. Thereby, the transmission data SD given to the input terminal I20
Is an RS232C signal S of + 12V or -12V, for example.
It is converted to D2 and output from the output terminal O20. At this time, an inverted signal of the RS232C signal SD is output from the output terminal O21.

During RS422 communication, the voltage + 5V is applied to the power supply terminal P20 of the buffer 20, and the inverter 21
The ground potential 0V is applied to the power supply terminal P21 of the. Thereby, the transmission data SD given to the input terminal I20 is converted into, for example, the RS422 signal SD4A of + 5V or 0V and the RS422 signal SD4B of 0V or + 5V, and output from the output terminals O20 and O21, respectively.

FIG. 4 is a circuit diagram showing the configuration of the differential receiving circuit 3. As shown in FIG. 4, the differential receiving circuit 3 includes a differential amplifier 30. The configuration of the differential receiving circuit 3 is shown in FIG.
The configuration is the same as that of the RS422 differential receiving circuit 15 shown in FIG.

The power supply terminal P30 of the differential amplifier 30 is always supplied with a voltage + 5V, and the ground terminal P31 is always supplied with a ground potential 0V. At the time of RS232C communication, the RS232C input terminal I30 of the differential amplifier 30 is limited to the range of 0 to + 5V by the clipping circuit 4 of FIG.
The signal RD2 is given, and the voltage of the input terminal I31 is fixed to + 2.5V by the pull-up resistor 9 of FIG.
As a result, RS232C signal RD2 and voltage + 2.5V
Is converted into the reception data RD and the output terminal O3
It is output from 0.

In the present embodiment, the voltage input to the input terminals I30 and I31 is set to 0 to +5 by using the clipping circuit 4.
Since the voltage is limited to within the range of V, when the input allowable voltage of the IC configuring the differential receiving circuit 3 is, for example, −2V to + 7V, the destruction of the IC is prevented.

During RS422 communication, RS422 of + 5V or 0V is applied to the input terminal I30 of the differential amplifier 30, for example.
The signal RD4A is applied to the input terminal I31 of, for example, 0V.
Alternatively, a + 5V RS422 signal RD4B is provided.
The RS422 signals RD4A and RD4B are converted into reception data RD and output from the output terminal O30.

FIG. 5 is a circuit diagram showing the configuration of the clipping circuit 4. As shown in FIG. 5, the clipping circuit 4
Is a Zener diode 4 having a Zener voltage of 5V
It consists of 0, 41, 42, 43. Zener diode 4
0, 41 limits the voltage applied between the input terminal I30 and the ground terminal within the range of 0 to +5 V, and the Zener diodes 42, 43 reduce the voltage applied between the input terminal I31 and the ground terminal. It is limited to the range of 0 to + 5V.

In the serial communication device of FIG. 1, the power supply voltage supplied to the differential transmission circuit 2 is switched by using the switches 5 and 6, whereby RS232C communication and RS
Data transmission in 422 communication is possible. Further, by limiting the voltage input to the differential receiving circuit 3 by using the clipping circuit 4, it is possible to receive data in RS232C communication and RS422 communication.

FIG. 6 is a circuit diagram showing another example of the power supply voltage switching circuit. The power supply voltage switching circuit of FIG.
Three-terminal regulator 50 that outputs the constant voltage of
Zener diode 5 having a zener voltage of 1 and 7 V
2 and switches 53 and 54.

Voltage + 15V is applied to positive power supply terminal P5, ground potential 0V is applied to ground terminal P6, and voltage -12V is applied to negative power supply terminal P7. The output terminal P8 is connected to the power supply terminal P20 of the differential transmission circuit 2 of FIG. 3, and the output terminal P9 is connected to the power supply terminal P21 of the differential transmission circuit 2.

During RS232C communication, the switch 53 is turned off. As a result, the voltage of the node N becomes + 7V by the Zener diode 52, and the voltage + 12V is output from the output terminal P8 by the three-terminal regulator 50. Further, the movable contact a of the switch 54 is switched to the contact b side. As a result, the voltage -1 is output from the output terminal P9.
2V is output.

During RS422 communication, the switch 53 is turned on. As a result, the voltage of the node N becomes 0V, and the three-terminal regulator 50 outputs the voltage + 5V from the output terminal P8. Further, the movable contact a of the switch 54 is switched to the contact c side. As a result, the potential of the output terminal P9 becomes 0V.

In the serial communication device of the above embodiment, the differential transmission circuit 2, the differential reception circuit 3, the output terminals O1,
Since O2 and the input terminals I1 and I2 are commonly used during RS232C communication and RS422 communication, the circuit scale is reduced. Therefore, it is possible to reduce the size and cost of the serial communication device.

The present invention is based on RS232C communication and RS4.
The present invention can be applied not only to the 22 communication but also to a serial communication device capable of performing serial communication according to other plural interface standards.

[0052]

As described above, according to the present invention, it is possible to obtain a serial communication device capable of serial communication complying with a plurality of interface standards with a small circuit scale. Therefore, it is possible to reduce the size and cost of the serial communication device.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a serial communication device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a serial communication control circuit shown in FIG.

FIG. 3 is a circuit diagram showing a configuration of a differential transmission circuit shown in FIG.

FIG. 4 is a circuit diagram showing a configuration of the differential receiving circuit shown in FIG.

5 is a circuit diagram showing a configuration of a clipping circuit shown in FIG.

FIG. 6 is a circuit diagram showing another example of a power supply voltage switching circuit.

FIG. 7 is a block diagram showing an example of a conventional serial communication device.

FIG. 8 is a block diagram showing another example of a conventional serial communication device.

9 is a circuit diagram showing a configuration of an RS232C transmission circuit shown in FIGS. 7 and 8. FIG.

10 is a circuit diagram showing a configuration of an RS422 differential transmission circuit shown in FIGS. 7 and 8. FIG.

11 is a circuit diagram showing a configuration of an RS232C receiving circuit shown in FIGS. 7 and 8. FIG.

12 is a circuit diagram showing a configuration of an RS422 differential receiving circuit shown in FIGS. 7 and 8. FIG.

[Explanation of symbols]

 1 Serial Communication Control Circuit 2 Differential Transmission Circuit 3 Differential Reception Circuit 4 Clipping Circuit 5, 6 Switch 7, 8 Current Limiting Resistor 9 Pull-up Resistor In addition, the same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A first complementary serial transmission data to each other.
And a second signal, which is converted into a differential signal,
And differential transmission means for serially transmitting either or both of the second signal and serially received differential signal or single signal and serially receiving the differential signal or single signal and a constant potential. A serial communication device comprising: a differential receiving means for converting into a differential voltage; and a power supply voltage switching means for switching a power supply voltage supplied to the differential transmitting means. 2. The serial communication device according to claim 1, further comprising voltage limiting means for limiting the voltage of the received differential signal or the received single signal within a predetermined range.