WO2012065494A1

WO2012065494A1 - Method and circuit for implementing serial port isolation

Info

Publication number: WO2012065494A1
Application number: PCT/CN2011/081128
Authority: WO
Inventors: 陆荣飞
Original assignee: 中兴通讯股份有限公司
Priority date: 2010-11-19
Filing date: 2011-10-21
Publication date: 2012-05-24
Also published as: CN102064821A; CN102064821B

Abstract

The present invention provides a method and a circuit for implementing serial port isolation, the method comprises: the RS232 level signal output via RS232 level serial port being converted to a pulse signal by the first transformer module，said pulse signal being converted to Transistor-Transistor Logic(TTL) level signal, and then being output to the TTL level serial port; depending on the received TTL level signal output via the TTL level serial port, choosing to output the high frequency signal to the second transformer module or the third transformer module, the received high frequency signal being converted to the RS232 negative level signal by the said second transformer module, the received high frequency signal being converted to the RS232 positive level signal by the said third transformer module, and then being output to said RS232 level serial port. The present invention can effectively suppress the static electricity and surge, and prevent the damage to the equipment serial port or the interference with equipment normal operation of ground loops and surges.

Description

Method for realizing serial port isolation and serial port isolation circuit

Technical field

The invention relates to the technical field of serial port signal isolation, in particular to a method for realizing serial port isolation by a transformer and a serial port isolation circuit.

Background technique

In a communication device, a serial port is usually drawn on the board as a communication port for debugging and monitoring of the board. However, sometimes the communication device is not shared with the host computer, or there is an indeterminate potential difference between the ground planes of the two communication devices. In addition, when the serial port is connected, it is usually hot swapped, and the discharge and surge between the two. It is easy to cause damage to the serial port or interfere with the normal operation of the communication device.

In order to solve the above problems, the related art often uses a serial port to take power and a photocoupler to form isolation, and the usual practice is as follows:

For example, the three-wire serial communication (that is, the serial connection method using only RX (receive data), TX (transmit data), and GND signals), as shown in Figure 1, includes the signals TXD, RXD, and GND1 of the serial RS232 level interface ( Signal ground), and serial port TTL (transistor-transistor logic) level interface signals ETXD, ERXD, GND2 (signal ground), optocoupler circuits Ul, U2, U3, voltage inverting circuit IC1. Wherein, the positive level signal of the input terminal TXD passes through the optocoupler circuit U3 to output the TTL level to the output terminal ERXD, and the other path passes through the path selection circuit to the optocoupler circuit U2 to provide the RS232 positive voltage; the input terminal TXD negative level signal After the path selection circuit is connected to the photoelectric isolation circuit U1, the RS232 negative voltage is supplied thereto, and the other circuit is passed through the voltage inversion circuit IC1 to the charging circuit. The voltage after charging provides the RS232 positive voltage to the optocoupler module U2.

Although this is feasible, it needs to be powered from the input terminal TXD to provide the RS232 level, which makes the TXD signal load larger. In addition, the RS232 negative voltage at the input is provided by the TXD negative level signal. If the TXD signal line transmits consecutive bytes 0x00 (ie, the TXD is positive except for the stop bit), the RS232 negative voltage is supplied to the RXD signal line. There may be insufficient.

Summary of the invention In order to overcome the deficiencies of the above technologies, the present invention provides a method for realizing serial port isolation and a serial port isolation circuit, which uses a transformer to realize three-wire serial port isolation, effectively suppressing static electricity and surge, and preventing ground loop and surge interference equipment. normal operation.

In order to solve the above technical problem, the present invention provides a serial port isolation circuit, including: a receiving circuit and a transmitting circuit, where

The receiving circuit includes a first transformer module and a pulse detection latch module.

The first transformer module is connected to the output end of the RS232 level serial port, and is configured to: receive the RS232 level signal output by the RS232 level serial port, convert the RS232 level signal into a positive and negative pulse signal, and output the signal to the pulse detection. Latch module

The pulse detection latch module is configured to: convert the positive and negative pulse signals into TTL level signals, and output the signals to the input end of the TTL level serial port;

The transmitting circuit includes a frequency driving module, a second transformer module and a third transformer module, and the frequency driving module is connected to the output end of the TTL level serial port, and is configured to: receive a TTL level of the output of the TTL level serial port a signal, according to the TTL level signal, selecting to output the high frequency signal to the second transformer module or the third transformer module;

The second transformer module is configured to: convert the received high frequency signal into an RS232 negative level signal, and output the signal to the receiving end of the RS232 level serial port;

The third transformer module is configured to: convert the received high frequency signal into an RS232 positive level signal, and output the signal to the receiving end of the RS232 level serial port.

The serial port isolation circuit may further have the following features: the first transformer module includes: a first transformer and a rectifier module,

The primary of the first transformer is connected to the output of the RS232 level serial port through a resistor, the secondary of the first transformer is connected to the rectifier module, and the rectifier module is connected to the pulse detection latch module. ;

The rectifier module is configured to: separately output a positive pulse signal and a negative pulse signal output by the first transformer to the pulse detection latch module;

The pulse detection latch module is configured to: convert the positive pulse signal to a TTL low level, and convert the negative pulse signal to a TTL high level. The serial port isolation circuit may further have the following features: The first transformer module includes: a current limiting protection module, wherein the rectifier module is connected to the pulse detection latch module by the current limiting protection module.

The serial port isolation circuit may further have the following features: the second transformer module includes: a second transformer and a first rectifying and filtering module, a primary of the second transformer is connected to the frequency driving module, and the second transformer is The first rectifying and filtering module is connected to the first rectifying and filtering module, the negative output end of the first rectifying and filtering module is connected to the receiving end of the RS232 level serial port, and the positive output end of the first rectifying and filtering module is grounded;

The third transformer module includes: a third transformer and a second rectifying and filtering module, a primary of the third transformer is connected to the frequency driving module, and a secondary of the third transformer is connected to the second rectifying and filtering module The positive output end of the second rectifying and filtering module is connected to the receiving end of the RS232 level serial port, and the negative output end of the second rectifying and filtering module is grounded.

The above serial port isolation circuit can also have the following features:

The second transformer module further includes: a first driving module that amplifies a current, a primary of the second transformer is connected to the frequency driving module by the first driving module;

The third transformer module further includes: a second driving module that amplifies the current, and the primary of the third transformer is connected to the frequency driving module through the second driving module.

The above serial port isolation circuit can also have the following features:

The pulse detection latch module is a digital integrated circuit, a complex programmable logic device or a field programmable gate array;

The frequency drive module is a digital integrated circuit, a complex programmable logic device, or a field programmable gate array.

A method for implementing serial port isolation based on the serial port isolation circuit described above, including:

Converting the RS232 level signal outputted by the RS232 level serial port into a pulse signal through the first transformer module, converting the pulse signal into a TTL level signal, and then outputting the signal to the input end of the TTL level serial port;

According to the TTL level signal of the output of the TTL level serial port, the high frequency signal is selected to be output to the second transformer module or the third transformer module, and the second transformer module will receive the high After the frequency signal is converted into an RS232 negative level signal, it is output to the receiving end of the RS232 level serial port, and the received high frequency signal is converted into an RS232 positive level signal by the third transformer module, and then output to the RS232 power. The receiving end of the flat serial port.

The above method may further have the following features: after the step of converting the RS232 level signal outputted by the RS232 level serial port into a pulse signal by the first transformer module, the method further includes: limiting the pulse signal.

The above method may further have the following features: after the step of converting the RS232 level signal outputted by the RS232 level serial port into a pulse signal by using the first transformer module, the method further includes:

The first transformer module separates the positive pulse signal and the negative pulse signal, and outputs the same to the pulse detection latch module.

The step of converting the pulse signal into a TTL level signal by the pulse detection latch module is specifically: the pulse detection latch module converts a positive pulse signal into a TTL low level, and converts the negative pulse signal into a TTL high power level.

The above method may further have the following features: Before the step of outputting the high frequency signal to the second transformer module or the third transformer module, the method further includes: amplifying the current of the high frequency signal.

The above method for realizing serial port isolation and the serial port isolation circuit are mainly designed for the three-wire serial communication mode, and do not need to take power from the serial signal line of the external device, and the extension is also applicable to the 5-wire RS232 communication and the full-line RS232 communication. The circuit structure is relatively simple, and the return paths of the isolated ends are not connected, which can effectively suppress static electricity and surge, and prevent the ground loop and surge from damaging the normal operation of the serial port or interference device of the device. BRIEF abstract

1 is a circuit diagram of a related art;

2 is a schematic diagram of the principle of a serial port isolation circuit according to an embodiment of the present invention;

3 is a schematic diagram of a serial port isolation circuit according to Embodiment 1 of the present invention;

4 is a schematic diagram of a serial port isolation circuit according to Embodiment 2 of the present invention; FIG. 5 is a flowchart of a method for implementing serial port isolation according to an embodiment of the present invention.

Preferred embodiment of the invention

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, in the case of no conflict, the features in the embodiments and the embodiments in the present application may be arbitrarily combined with each other.

In the embodiment of the invention, the signal of the serial port (such as the RS232 level serial port and the TTL level serial port) between the two devices is isolated by the transformer, and the conversion between the RS232 level and the TTL level of the serial port is realized at the same time. Wherein, in the receiving circuit, the input signal of the RS232 level is converted into a positive pulse or a negative pulse by the transformer through the transformer, and then the positive pulse and the negative pulse are separated by the rectifier module, and then sent to the pulse detection latch. The module, the function of the pulse detection latch module is to discriminate and latch the input pulse signal, and output a TTL level signal to the TTL level serial port. In the transmitting circuit, the TTL level signal is sent to the frequency driving module. After the frequency driving module discriminates the input TXD signal, it outputs a higher frequency signal to a different transformer. After the transformer is boosted and the rectifier circuit is rectified, the RS232 is sent to the RS232. The level serial port outputs the positive or negative level of RS232.

The principle of the serial port isolation circuit according to the embodiment of the present invention is as shown in FIG. 2, which includes two parts of the receiving circuit and the transmitting circuit:

The upper part of the figure is a receiving circuit, comprising: a first transformer module and a pulse detecting latch module, wherein

The first transformer module is connected to the output end of the RS232 level serial port, and is configured to receive the RS232 level signal output by the RS232 level serial port, convert the RS232 level signal into a positive and negative pulse signal, and output the signal to the pulse detection lock. Storage module

The pulse detection latch module is configured to convert the positive and negative pulse signals into a TTL level signal and output the signal to a TTL level serial port input.

The first transformer module may include: a first transformer and a rectification module, wherein a primary of the first transformer is connected to an output end of the RS232 level serial port through a resistor Connected, the secondary of the first transformer is connected to the rectifier module, and the rectifier module is connected to the pulse detection latch module;

The rectifier module is configured to separately output a positive pulse signal and a negative pulse signal output by the first transformer to the pulse detection latch module;

The pulse detection latch module is configured to convert a positive pulse signal to a TTL low level and a negative pulse signal to a TTL high level.

The first transformer module may further include: a current limiting protection module, wherein the rectifier module is connected to the pulse detection latch module by the current limiting protection module.

The lower part of the figure is a transmitting circuit, comprising: a frequency driving module, a second transformer module and a third transformer module, wherein

a frequency driving module, connected to the output end of the TTL level serial port, configured to receive a TTL level signal of the output of the TTL level serial port, and outputting the high frequency signal to the second transformer according to the TTL level signal Module or third transformer module;

The second transformer module is configured to convert the received high frequency signal into an RS232 positive level signal, and output the signal to the receiving end of the RS232 level serial port;

The third transformer module is configured to convert the received high frequency signal into an RS232 negative level signal and output the signal to the receiving end of the RS232 level serial port.

The second transformer module includes: a second transformer and a first rectifying and filtering module, a primary of the second transformer is connected to the frequency driving module, a secondary of the second transformer, and the first rectifying filter The module is connected, the negative output end of the first rectifying and filtering module is connected to the receiving end of the RS232 level serial port, and the positive output end of the first rectifying and filtering module is grounded; the second transformer module may further include: a first driving module of the current, the primary of the second transformer being connected to the frequency driving module by the first driving module.

The third transformer module may include: a third transformer and a second rectifying and filtering module, wherein a primary of the third transformer is connected to the frequency driving module, and a secondary of the third transformer and the second rectifying and filtering module The positive output end of the second rectifying and filtering module is connected to the receiving end of the RS232 level serial port, and the negative output end of the second rectifying and filtering module is grounded. The third change The voltage module may further include: a second driving module that amplifies the current, and the primary of the third transformer is connected to the frequency driving module through the second driving module.

The serial port isolation circuit can be implemented in two ways: one is to integrate the serial port isolation circuit into the single board; the other is to make the serial port isolation circuit into a separate small board for connecting, for example, an RS232 level serial port and a single computer. TTL level serial port on the board.

3 is a schematic diagram of a serial port isolation circuit according to Embodiment 1 of the present invention, as shown in FIG. 3: The upper part of the figure is a receiving circuit, wherein an R232 signal line on the receiving end transmits an RS232 level signal, which is connected to an external device. RS232 level serial port (such as PC) output; RX signal is connected to the primary of the transformer through a resistor, the function of the resistor is current limiting and impedance matching, the transformer realizes the isolation of the signal ground on both sides and converts the RX signal into a pulse signal; The pulse signal of the secondary output of the transformer is rectified by a rectifier module composed of four diodes, and then sent to the A or B terminal of the pulse detection latch circuit; the pulse detection latch circuit converts the pulse signal of the A or B terminal into a TTL of 0 or 1. The level signal is sent to the receiving end of the TTL level serial port of the board (such as the CPU) through the RXD signal line.

The basic principle of the receiving circuit is that when the level on the RX jumps, a pulse is generated at the secondary of the transformer. Through the rectification of the diode, the positive transition (the RX signal changes from a negative level to a positive level, that is, the current direction of the transformer primary changes from the direction of b to a to the direction from a to b, the direction of the voltage generated in the secondary The pulse generated for a, high level, b, low level is sent to the A terminal in the figure, and the negative transition (the RX signal changes from positive to negative, that is, the current direction of the transformer primary is from a to b. The direction of the direction becomes from b to a, and the voltage generated in the secondary direction is b, high level, a, low level. The generated pulse is sent to the B terminal in the figure. The function of the pulse detection latch circuit is to convert the pulse signal into a TTL level signal. When the pulse of the A terminal is detected, the RXD signal line is set to a low level, and when the pulse of the B end is detected, the RXD signal line is set. Is high. The pulse detection latch circuit can be implemented by a digital IC (integrated circuit), a CPLD or an FPGA (Field-Programmable Gate Array).

The lower part of the figure is the TTL of the transmitting circuit, the TXD signal line and the board (such as the CPU). The transmitting end of the flat serial port is connected, and the C port of the frequency driving module is connected to a transformer primary. The secondary of the transformer is connected with a rectifying and filtering circuit composed of a diode, a capacitor, a resistor and a triode, and the negative output end of the rectifying and filtering circuit and the RS232 level are connected. The receiving end of the serial port (for example, the serial port of the computer) is connected, and the positive output end of the rectifying and filtering circuit is grounded; the D port of the frequency driving module is connected to the primary of the other transformer, and the secondary of the transformer is rectified by a diode, a capacitor, a resistor, and a triode. The filter circuit is connected; the positive output end of the rectification and filtering circuit is connected to the receiving end of the RS232 level serial port (for example, a computer serial port), and the negative output end of the rectifying and filtering circuit is grounded.

The basic principle of the transmitting circuit is that the TXD signal of the CPU serial port is sent to the frequency driving module, and the frequency driving module can be implemented by a digital IC, a CPLD or an FPGA. When the TXD signal is 0, the high frequency signal (relative to the serial port baud rate) is output from the D terminal. After the transformer boost and the rectifier circuit, the RS232 positive level is output at the TX terminal; when the TXD signal is 1, The high-frequency signal is converted to output from the C terminal. After the transformer is boosted and the rectifier circuit is turned on, the negative level of RS232 is output at the TX terminal, wherein the TX signal line is connected to the serial port receiving end of an external device (for example, a PC).

4 is a schematic diagram of a serial port isolation circuit according to Embodiment 2 of the present invention, as shown in FIG. 4: The circuit of this embodiment includes two parts of receiving and transmitting circuits:

Receiving circuit: The circuit is connected in the same way as the receiving circuit of Figure 3. The difference is that the resistors, capacitors and Zener diodes are added to the A and B ports to realize pulse shaping and overvoltage protection, and CPLD (Complex) is used. Programmable Logic Device, a complex programmable logic device, implements the function of a "pulse detection latch circuit".

The RX signal line on the receiving end transmits an RS232 level signal that is connected to the output of an external device (such as a PC). When the level on RX jumps, a pulse is generated at the secondary of the transformer. After diode rectification, the pulse generated by the positive transition (the negative level on RX becomes positive) is sent to the A terminal of the figure, and the pulse generated by the negative transition (positive level of RX becomes negative). Will be sent to the B end of the figure. The function of the "pulse detection latch circuit" is to set the value of the latch to 0 when the pulse of the A terminal is detected, and output it to the RXD signal line, and send it to the serial port receiving end of the CPU; At the end of the pulse, the value of the latch is set to 1 and output to the RXD signal line. In addition, the resistor in the figure acts as a current limiting capacitor, the capacitor acts as a shaping, and the protection diode is used to limit the pulse voltage applied to the A and B terminals. Transmitting circuit: The circuit is connected in the same way as the transmitting circuit of Figure 3. The difference is that the transistor is used in the primary of the transformer to enhance the driving ability of the signal, and the CPLD is used to realize the function of "frequency generation and driving circuit".

The TXD signal of the CPU serial port is sent to the "selector" in the CPLD. The "selector" is added with the "frequency generator", which is equivalent to the frequency drive module of Figure 3. When the TXD signal is 0, the high frequency signal (relative to the serial port baud rate) is output from the D terminal. After the switching boost circuit composed of the transistor and the transformer, the RS232 positive output is output at the TX terminal; when the TXD signal is At 1 o'clock, the high-frequency signal is converted to output from the C terminal. After the switching boost circuit composed of the transistor and the transformer, the negative level of RS232 is output at the TX terminal. The TX signal line is connected to the serial port receiving end of an external device (such as a PC). In this embodiment, the switching boost circuit is used because the circuit has a relatively small dependence on the transformer turns ratio, and the amplitude of the output voltage can be conveniently adjusted by changing the duty ratio of the frequency generator. Since the switching booster circuit is a general-purpose switching power supply technology, it will not be described in detail in this embodiment.

The rectifying module in the embodiment of the present invention is not limited to being composed of four diodes. Of course, other devices (for example, a triode, a field effect transistor) may be used, and the rectifying and filtering circuit is not limited to the electronic device composition shown in the figure.

FIG. 5 is a flowchart of a method for implementing serial port isolation according to the present invention. The method is implemented by the serial port isolation circuit, as shown in FIG. 5, and includes the following steps:

S10. After converting the RS232 level signal outputted by the RS232 level serial port into a positive and negative pulse signal through the first transformer module, converting the positive and negative pulse signals into a TTL level signal, and then outputting the signal to the TTL level serial port;

S20. Select, according to the TTL level signal that receives the output of the TTL level serial port, output the high frequency signal to the second transformer module or the third transformer module, and convert the received high frequency signal into the RS232 negative power by using the second transformer module. The flat signal is output to the receiving end of the RS232 level serial port, and the received high frequency signal is converted into an RS232 positive level signal by the third transformer module, and then output to the RS232 level serial port.

Wherein, in step S10, the first transformer module outputs RS232 of the RS232 level serial port. After the level signal is converted into a positive and negative pulse signal, it may further include:

The step of converting the positive and negative pulse signals into the TTL level signals by the pulse detection latch module is specifically: the pulse detection latch module converts the positive pulse signal into a TTL low level, and converts the negative pulse signal into a TTL High level.

In the step S20, before the outputting the high frequency signal to the second transformer module or the third transformer module, the method further includes: amplifying the current of the high frequency signal to enhance the driving capability of the transformer.

One of ordinary skill in the art will appreciate that all or a portion of the above steps may be accomplished by a program that instructs the associated hardware to be stored in a computer readable storage medium, such as a read only memory, a magnetic disk, or an optical disk. Alternatively, all or part of the steps of the above embodiments may also be implemented using one or more integrated circuits. Correspondingly, each module/unit in the above embodiment may be implemented in the form of hardware or in the form of a software function module. The invention is not limited to any specific form of combination of hardware and software.

The above embodiments are only intended to illustrate the technical solutions of the present invention and are not to be construed as limiting the invention. It should be understood by those skilled in the art that the present invention may be modified or equivalently substituted without departing from the spirit and scope of the invention.

Industrial Applicability The above-mentioned embodiment is mainly designed for the three-wire serial communication mode. It does not need to take power from the serial signal line of the external device. By extending, it is also applicable to 5-wire RS232 communication and full-line RS232 communication. The circuit structure is relatively simple, and the return paths of the isolated ends are not connected, which can effectively suppress static electricity and surge, and prevent the ground loop and surge from damaging the serial port of the device or disturbing the normal operation of the device.

Claims

Claim

A serial port isolation circuit, comprising: a receiving circuit and a transmitting circuit, wherein

The first transformer module is connected to an output end of the RS232 level serial port, and is configured to: receive an RS232 level signal output by the RS232 level serial port, convert the RS232 level signal into a positive and negative pulse signal, and output the same to the office a pulse detection latch module;

The pulse detection latch module is configured to: convert the positive and negative pulse signals into a transistor-transistor logic (TTL) level signal, and output the signal to an input end of the TTL level serial port;

The transmitting circuit includes a frequency driving module, a second transformer module and a third transformer module, wherein the frequency driving module is connected to an output end of the TTL level serial port, and is configured to: receive a TTL of the output of the TTL level serial port Level signal, selecting to output the high frequency signal to the second transformer module or the third transformer module according to the TTL level signal;

2. The serial port isolation circuit of claim 1, wherein: said first transformer module comprises: a first transformer and a rectifier module,

The pulse detection latch module is configured to: convert the positive pulse signal to a TTL low level, and convert the negative pulse signal to a TTL high level.

3. The serial port isolation circuit of claim 2, wherein: said first transformer module comprises: a current limiting protection module, said rectifier module passing said current limiting protection module and said pulse detection latching mode Block connection.

4. The serial port isolation circuit of claim 1, wherein:

The second transformer module includes: a second transformer and a first rectifying and filtering module, a primary of the second transformer is connected to the frequency driving module, and a secondary of the second transformer is connected to the first rectifying and filtering module The negative output end of the first rectifying and filtering module is connected to the receiving end of the RS232 level serial port, and the positive output end of the first rectifying and filtering module is grounded;

5. The serial port isolation circuit of claim 4, wherein:

6. The serial port isolation circuit according to any one of claims 1 to 5, wherein:

The pulse detection latch module is a digital integrated circuit, a complex programmable logic device or a field programmable gate array; the frequency drive module is a digital integrated circuit, a complex programmable logic device or a field programmable gate array.

7. A method for implementing serial port isolation based on the serial port isolation circuit of claim 1, comprising:

The RS232 level signal outputted by the RS232 level serial port is converted into a pulse signal by the first transformer module, and the pulse signal is converted into a TTL level signal, and then output to a TTL level serial port; according to the output of the TTL level serial port received The TTL level signal is selected to output the high frequency signal to the second transformer module or the third transformer module, and the received high frequency signal is converted into the RS232 negative level signal by the second transformer module, and then output to the RS232 power The receiving end of the flat serial port converts the received high frequency signal into an RS232 positive level signal through the third transformer module, and then inputs The RS232 level serial port is sent out.

8. The method according to claim 7, further comprising: after the step of converting the RS232 level signal outputted by the RS232 level serial port into a pulse signal by using the first transformer module,

The pulse signal is current limited.

The method according to claim 7 or 8, after the step of converting the RS232 level signal outputted by the RS232 level serial port into a pulse signal by the first transformer module, further comprising:

10. The method of claim 7, further comprising: before the step of selecting to output the high frequency signal to the second transformer module or the third transformer module, further comprising:

Amplifying the current of the high frequency signal.