Circuit for realizing high-speed isolation of serial port RS485 by using low-speed optocoupler

Abstract

The utility model relates to a circuit for realizing high-speed isolation of a serial port RS485 by using a low-speed optocoupler. The circuit comprises a main chip U2, a sending isolation circuit, a receiving isolation circuit, a sending driving amplification circuit, a receiving driving amplification circuit and an enable signal generation circuit. According to the circuit for realizing high-speed isolation of the serial port RS485 by using the low-speed optical coupler, the use of an RTS pin is canceled, a signal is led out from the TXD end of the serial port, and an enable signal is realized through the high-speed inverter, so that the problems in the prior art are solved, the safety performance of an RS485 communication interface is improved, the requirements of isolation, high speed and low cost are met, the use of an optical coupler device is reduced, and the cost is reduced. Meanwhile, manufacturing cost is reduced, and production efficiency is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of light source accessory equipment, in particular to a circuit for realizing high-speed isolation serial port RS485 by using a low-speed optical coupler. Background Art

[0002] In the existing industrial control field, RS485 communication protocol is widely used. It has the advantages of long transmission distance and strong anti-interference ability. However, the traditional RS485 communication interface does not take into account the problem of electrical isolation, which is insufficient in some occasions with high safety requirements, such as power systems and medical equipment. Therefore, it is of great practical significance to study an RS485 circuit implementation scheme that can realize high-speed isolated serial port. At present, high-speed optocouplers are generally used to realize the electrical isolation of RS485 communication interface. However, the manufacturing cost of high-speed optocouplers is high, and problems such as signal distortion and transmission delay may occur during high-speed transmission. In addition, the existing isolation scheme has certain limitations in circuit design and signal integrity, which limits its application in the field of high-speed communication. The conventional UART serial port to RS485 bus circuit requires the three signal lines of RXD, TXD, and RTS to pass through three optocouplers to realize data transmission, and it is impossible to achieve high-speed transmission under isolation. Utility Model Content

[0003] In view of this, it is necessary to provide a circuit for reducing signal lines and realizing high-speed isolation serial port RS485 using low-speed optical couplers under isolation conditions.

[0004] A circuit for realizing high-speed isolation of serial port RS485 using low-speed optical coupler comprises a main chip U2, a transmission isolation circuit, a reception isolation circuit, a transmission drive amplifier circuit, a reception drive amplifier circuit, an enable signal generating circuit, a resistor R1, a resistor R11, a capacitor C1, and a capacitor C3. The main chip U2 is a serial port RS485 conversion chip, comprising a reception input pin DO, a drive input pin DI, a reception output enable pin / RE, a drive output enable pin DE, a reception input and drive output pin A, and a reception input and drive output pin B, and is used for converting serial port UART signals to RS485 differential signals. The serial port TXD transmission terminal is connected to the input end of the transmission isolation circuit, the output end of the transmission isolation circuit is connected to the input end of the transmission drive amplifier circuit, and the output end of the transmission drive amplifier circuit is connected to the drive input pin DI of the main chip U2 and the enable signal generating circuit. The input end of the receiving isolation circuit is connected to the receiving input pin DO of the main chip U2, the output end of the receiving isolation circuit is connected to the input end of the receiving drive amplifier circuit, the serial port RXD receiving end is connected to the output end of the receiving drive amplifier circuit, the output end of the enable signal generating circuit is connected to the receiving output enable pin / RE and the driving output enable pin DE of the main chip U2, the receiving input and driving output pin A of the main chip U2 are connected to the first end of the resistor R1, the second end of the resistor R1 is connected to the isolation power supply VCC_COM1, the receiving input and driving output pin A of the main chip U2 are connected to the first end of the resistor R11, the second end of the resistor R11 is connected to the isolation power supply VCC_COM1, the capacitor C1 and the capacitor C3 are the filter capacitors of the isolation power supply VCC_COM1, the high frequency and low frequency noise filtering, decoupling, and providing peak current support for the RS485 circuit.

[0005] Furthermore, the transmission isolation circuit includes an optocoupler U1, a capacitor C2, and a resistor R4. Pin 2 of the optocoupler U1 is connected to the serial port TXD transmitting end, and pin 4 of the optocoupler U1 is connected to the isolated power supply VCC_COM1. The first end of the resistor R4 is connected to pin 1 of the optocoupler U1, and the second end of the resistor R4 is connected to the power supply 3.3V. The first end of the capacitor C2 is connected to pin 1 of the optocoupler U1, and the second end of the capacitor C2 is connected to the power supply 3.3V. The optocoupler U1 is used for the isolated transmission of the serial port transmission signal to prevent electrical noise interference and ensure the accurate transmission of the transmission signal. R4 is a series resistor for pulling up the input signal of the optocoupler U1, which limits the current on the input side of the optocoupler and improves the rise and fall time of the optocoupler. The capacitor C2 is a pull-up filter capacitor for the input signal of the optocoupler U1 to suppress high-frequency interference signals and improve the power supply quality.

[0006] Furthermore, the receiving isolation circuit includes an optocoupler U3, a capacitor C4, and a resistor R7. The first end of the resistor R7 is connected to the first pin of the optocoupler U2, the second pin of the optocoupler U3 receives the input end of the isolation circuit, the second end of the resistor R7 is connected to the isolation power supply VCC_COM1, the first end of the capacitor C4 is connected to the first pin of the optocoupler U3, and the second end of the capacitor C4 is connected to the isolation power supply VCC_COM1. The optocoupler U3 is used for the isolated transmission of the serial port receiving signal to prevent electrical noise interference and ensure the accurate transmission of the received signal. R7 is a series resistor for pulling up the input signal of the optocoupler U3, which limits the current on the input side of the optocoupler and improves the rise and fall time of the optocoupler. The capacitor C4 is a pull-up filter capacitor for the input signal of the optocoupler U3, which suppresses high-frequency interference signals and improves the power quality.

[0007] Furthermore, the transmitting drive amplifier circuit includes a transistor Q1, a resistor R2, and a resistor R5. The base of the transistor Q1 is connected to the input end of the transmitting drive amplifier circuit and the first end of the resistor R5. The emitter of the transistor Q1 and the second end of the resistor R5 are grounded. The collector of the transistor Q1 is connected to the output end of the transmitting drive amplifier circuit and the first end of the resistor R2. The second end of the resistor R2 is connected to the isolated power supply VCC_COM1. The transistor Q1 is used in the transmitting drive amplifier circuit to amplify the output current on the output side of the optocoupler U1 to increase the circuit driving capability.

[0008] Furthermore, the receiving drive amplifier circuit includes a transistor Q2, a resistor R6, and a resistor R10. The base of the transistor Q2 is connected to the output end of the receiving drive amplifier circuit and the first end of the resistor R10. The emitter of the transistor Q2 and the second end of the resistor R10 are grounded. The collector of the transistor Q2 is connected to the output end of the receiving drive amplifier circuit and the first end of the resistor R6. The second end of the resistor R6 is connected to the power supply 3.3V. The transistor Q2 is used in the receiving drive amplifier circuit to amplify the output current on the output side of the optocoupler U2 to increase the circuit driving capability.

[0009] Furthermore, the enable signal generating circuit includes a diode D1, a resistor R12, an inverter U4, and a capacitor C5. The cathode of the diode D1 is the input end of the enable signal generating circuit, and is connected to the first end of the resistor R12 and the output end of the sending drive amplifier circuit. The anode of the diode D1 is connected to the input pin 1 of the inverter U4, the input pin 2 of the inverter U4, the second end of the resistor R12, and the first end of the capacitor C5. The output pin 4 of the inverter U4 is connected to the output end of the enable signal generating circuit. The second end of the capacitor C5 is grounded. The inverter U4 performs reverse processing on the input signal.

[0010] The input end of the enable signal generating circuit obtains the TXD signal from the output end of the drive amplifier circuit, and after reverse processing by the inverter U4, it is sent to the receiving output enable pin / RE and the driving output enable pin DE of the main chip U2 through the output end of the enable signal generating circuit; when the TXD signal is at a high level, the receiving output enable pin / RE and the driving output enable pin DE input of the main chip U2 are low, and the main chip is in a receiving state; when the TXD signal is at a low level, the receiving output enable pin / RE and the driving output enable pin DE input of the main chip U2 are high, and the main chip U2 is in a sending state; when the main chip U2 is in a receiving state, the signals input from the D1+ and D1- ends of the RS485 bus are received and converted by the main chip U2 to output data signals from the receiving output pin RO, and through the interface The receiving isolation circuit amplifies the signal and sends it to the receiving drive circuit, which is amplified by the receiving drive circuit and output from the serial port RXD end to the serial port UART; when the main chip U2 is in the sending state, the TXD signal sent by the serial port TXD end is amplified by the sending isolation circuit and sent to the sending drive circuit, which is amplified by the sending drive circuit and sent to the drive input pin DI of the main chip U2. When the TXD signal is at a low level, the enable signal generates an electrical circuit reverse processing, and the receiving output enable pin / RE and the drive output enable pin DE of the main chip U2 are high. The main chip U2 converts the TXD signal into an RS485 bus signal, which is transmitted to the RS485 bus D1+ and D1- ends through the receiving input and drive output pin A and the receiving input and drive output pin B of the main chip U2, and output to the RS485 bus.

[0011] Furthermore, the circuit for implementing high-speed isolated serial port RS485 using low-speed optocoupler also includes an RS485 bus protection device, wherein the semiconductor discharge tube TV1, the resistor R3, the resistor R9, the resettable fuse F1, and the resettable fuse F2 are RS485 bus protection devices, the first terminal of the semiconductor discharge tube TV1 is connected to the second end of the resistor R3, the first end of the resistor R3 is connected to the receiving input and driving output pin A of the main chip U2, the second end of the resistor R3 is connected to the D1+ end of the RS485 bus through the resettable fuse F1, the second terminal of the semiconductor discharge tube TV1 is connected to the second end of the resistor R9, the first end of the resistor R9 is connected to the receiving input and driving output pin B of the main chip U2, the second end of the resistor R9 is connected to the D1- end of the RS485 bus through the resettable fuse F2, the first ends of the capacitors C1 and C3 are connected to the isolated power supply VCC_COM1, the second ends of the capacitors C1 and C3 are grounded, the capacitors C1 and C3 are filter capacitors of the isolated power supply VCC_COM1, and are used for high-frequency and low-frequency noise filtering, decoupling, and providing peak current support for the circuit.

[0012] The circuit using low-speed optical coupler to realize high-speed isolation serial port RS485, the model of main chip U2 is GM3085.

[0013] In the above circuit that uses low-speed optocouplers to realize high-speed isolated serial port RS485, the use of the RTS pin is cancelled, and a signal is led out from the serial port TXD end, and an enable signal is realized through a high-speed inverter, thereby solving the problems existing in the prior art, improving the safety performance of the RS485 communication interface, improving the stability and reliability of signal transmission, meeting the application requirements of isolation, high speed and low cost, reducing the use of optocoupler devices, simplifying the circuit structure, reducing manufacturing costs, and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The utility model is a circuit schematic diagram of an embodiment of the invention that uses a low-speed optical coupler to realize a high-speed isolated serial port RS485. DETAILED DESCRIPTION

[0015] The present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0016] See also Figure 1, showing a circuit for realizing high-speed isolation serial port RS485 using low-speed optical coupler provided by an embodiment of the utility model, including a main chip U2, a transmission isolation circuit, a reception isolation circuit, a transmission drive amplifier circuit, a reception drive amplifier circuit, an enable signal generating circuit, a resistor R1, a resistor R11, a capacitor C1, and a capacitor C3. The main chip U2 is a serial port RS485 conversion chip, including a reception input pin DO, a drive input pin DI, a reception output enable pin / RE, a drive output enable pin DE, a reception input and drive output pin A, and a reception input and drive output pin B, which are used for converting serial port UART signals to RS485 differential signals. The serial port TXD transmission terminal is connected to the input end of the transmission isolation circuit, and the output end of the transmission isolation circuit is connected to the input end of the transmission drive amplifier circuit. The transmission drive amplifier circuit The output end is connected to the driving input pin DI of the main chip U2 and the input end of the enable signal generating circuit, the receiving isolation circuit input end is connected to the receiving input pin DO of the main chip U2, the receiving isolation circuit output end is connected to the input end of the receiving driving amplifier circuit, the serial port RXD receiving end is connected to the output end of the receiving driving amplifier circuit, the output end of the enable signal generating circuit is connected to the receiving output enable pin / RE and the driving output enable pin DE of the main chip U2, the receiving input and driving output pin A of the main chip U2 are connected to the first end of the resistor R1, the second end of the resistor R1 is connected to the isolation power supply VCC_COM1, the receiving input and driving output pin A of the main chip U2 are connected to the first end of the resistor R11, the second end of the resistor R11 is connected to the isolation power supply VCC_COM1, and the resistors R1 and R11 are RS485 respectively. The pull-up bias resistor and pull-down bias resistor of the differential line in the bus circuit are used to improve the RS485 bus's resistance to common-mode interference. Capacitor C1 and capacitor C3 are filter capacitors of the isolated power supply VCC_COM1, which are used for high-frequency and low-frequency noise filtering and decoupling, and provide peak current support for the RS485 circuit.

[0017] Furthermore, the sending isolation circuit includes an optocoupler U1, a capacitor C2, and a resistor R4. Pin 2 of the optocoupler U1 is connected to the serial port TXD sending end, and pin 4 of the optocoupler U1 is connected to the isolated power supply VCC_COM1. The first end of the resistor R4 is connected to pin 1 of the optocoupler U1, and the second end of the resistor R4 is connected to the power supply 3.3V. The first end of the capacitor C2 is connected to pin 1 of the optocoupler U1, and the second end of the capacitor C2 is connected to the power supply 3.3V. The optocoupler U1 is used for the isolated transmission of the serial port sending signal to prevent electrical noise interference and ensure the accurate transmission of the sending signal. The resistor R4 is a series resistor for pulling up the input signal of the optocoupler U1, which is used to limit the current on the input side of the optocoupler to increase the rise and fall time of the optocoupler. The capacitor C2 is a pull-up filter capacitor for the input signal of the optocoupler U1, which is used to suppress high-frequency interference signals and improve the power supply quality.

[0018] Furthermore, the receiving isolation circuit includes an optocoupler U3, a capacitor C4, and a resistor R7. The first end of the resistor R7 is connected to the first pin of the optocoupler U2, the second pin of the optocoupler U3 is connected to the input end of the receiving isolation circuit, the second end of the resistor R7 is connected to the isolation power supply VCC_COM1, the first end of the capacitor C4 is connected to the first pin of the optocoupler U3, and the second end of the capacitor C4 is connected to the isolation power supply VCC_COM1. The optocoupler U3 is used for the isolated transmission of the serial port receiving signal to prevent electrical noise interference and ensure the accurate transmission of the received signal. The resistor R7 is a series resistor for pulling up the input signal of the optocoupler U3, which is used to limit the current on the input side of the optocoupler to increase the rise and fall time of the optocoupler. The capacitor C4 is a pull-up filter capacitor for the input signal of the optocoupler U3, which is used to suppress high-frequency interference signals and improve power quality.

[0019] Furthermore, the transmitting drive amplifier circuit includes a transistor Q1, a resistor R2, and a resistor R5. The base of the transistor Q1 is connected to the input end of the transmitting drive amplifier circuit and the first end of the resistor R5. The emitter of the transistor Q1 and the second end of the resistor R5 are grounded. The collector of the transistor Q1 is connected to the output end of the transmitting drive amplifier circuit and the first end of the resistor R2. The second end of the resistor R2 is connected to the isolated power supply VCC_COM1. The transistor Q1 is used in the transmitting drive amplifier circuit to amplify the output current on the output side of the optocoupler U1 to increase the circuit driving capability.

[0020] Furthermore, the receiving drive amplifier circuit includes a transistor Q2, a resistor R6, and a resistor R10. The base of the transistor Q2 is connected to the input end of the receiving drive amplifier circuit and the first end of the resistor R10. The emitter of the transistor Q2 and the second end of the resistor R10 are grounded. The collector of the transistor Q2 is connected to the output end of the receiving drive amplifier circuit and the first end of the resistor R6. The second end of the resistor R6 is connected to the power supply 3.3V. The transistor Q2 is used in the receiving drive amplifier circuit to amplify the output current on the output side of the optocoupler U3 to increase the circuit driving capability.

[0021] Furthermore, the enable signal generating circuit includes a diode D1, a resistor R12, an inverter U4, and a capacitor C5. The cathode of the diode D1 is the input end of the enable signal generating circuit, and is connected to the first end of the resistor R12 and the output end of the sending drive amplifier circuit. The anode of the diode D1 is connected to the input pin 1 of the inverter U4, the input pin 2 of the inverter U4, the second end of the resistor R12, and the first end of the capacitor C5. The output pin 4 of the inverter U4 is connected to the output end of the enable signal generating circuit. The second end of the capacitor C5 is grounded. The inverter U4 performs reverse processing on the input signal.

[0022] The input end of the enable signal generating circuit obtains the TXD signal from the output end of the drive amplifier circuit, and after reverse processing by the inverter U4, it is sent to the receiving output enable pin / RE and the driving output enable pin DE of the main chip U2 through the output end of the enable signal generating circuit; when the TXD signal is at a high level, the receiving output enable pin / RE and the driving output enable pin DE input of the main chip U2 are low, and the main chip is in a receiving state; when the TXD signal is at a low level, the receiving output enable pin / RE and the driving output enable pin DE input of the main chip U2 are high, and the main chip U2 is in a sending state; when the main chip U2 is in a receiving state, the signals input from the D1+ and D1- ends of the RS485 bus are received and converted by the main chip U2 to output data from the receiving output pin RO, and the main chip U2 receives and converts the signals ... The receiving isolation circuit amplifies the signal and sends it to the receiving drive circuit, which is amplified by the receiving drive circuit and then output from the serial port RXD end to the serial port UART. When the main chip U2 is in the sending state, the TXD signal sent by the serial port TXD end is amplified by the sending isolation circuit and sent to the sending drive circuit. After being amplified by the sending drive circuit, it is sent to the drive input pin DI of the main chip U2. When the TXD signal is at a low level, the enable signal circuit is reversely processed, and the receiving output enable pin / RE and the drive output enable pin DE of the main chip U2 are high. The main chip U2 converts the TXD signal into an RS485 bus signal, and transmits it to the RS485 bus D1+ and D1- ends through the receiving input and drive output pin A and the receiving input and drive output pin B of the main chip U2, and then outputs it to the RS485 bus.

[0023] Furthermore, the circuit for implementing high-speed isolated serial port RS485 using low-speed optocoupler also includes an RS485 bus protection device, wherein the semiconductor discharge tube TV1, the resistor R3, the resistor R9, the resettable fuse F1, and the resettable fuse F2 are RS485 bus protection devices, the first terminal of the semiconductor discharge tube TV1 is connected to the second end of the resistor R3, the first end of the resistor R3 is connected to the receiving input and driving output pin A of the main chip U2, the second end of the resistor R3 is connected to the D1+ end of the RS485 bus through the resettable fuse F1, the second terminal of the semiconductor discharge tube TV1 is connected to the second end of the resistor R9, the first end of the resistor R9 is connected to the receiving input and driving output pin B of the main chip U2, the second end of the resistor R9 is connected to the D1- end of the RS485 bus through the resettable fuse F2, the first ends of the capacitors C1 and C3 are connected to the isolated power supply VCC_COM1, the second ends of the capacitors C1 and C3 are grounded, the capacitors C1 and C3 are filter capacitors of the isolated power supply VCC_COM1, and are used for high-frequency and low-frequency noise filtering, decoupling, and providing peak current support for the circuit.

[0024] The circuit using low-speed optical coupler to realize high-speed isolation serial port RS485, the model of main chip U2 is GM3085.

[0025] In the above circuit that uses low-speed optocouplers to realize high-speed isolated serial port RS485, the use of the RTS pin is cancelled, and the signal is led out from the TXD end of the serial port, and the enable signal is realized through a high-speed inverter, so as to solve the problems existing in the prior art, improve the safety performance of the RS485 communication interface, improve the stability and reliability of signal transmission, meet the application requirements of isolation, high speed and low cost, reduce the use of optocoupler devices, simplify the circuit structure, reduce the manufacturing cost, and improve the production efficiency.

[0026] It should be noted that the present invention is not limited to the above-mentioned embodiments. According to the creative spirit of the present invention, those skilled in the art may also make other changes. These changes made according to the creative spirit of the present invention should be included in the scope of protection required by the present invention.

Claims

1. A circuit for realizing high-speed isolation serial port RS485 using low-speed optical coupler, characterized in that: The invention comprises a main chip U2, a transmission isolation circuit, a reception isolation circuit, a transmission drive amplifier circuit, a reception drive amplifier circuit, an enable signal generating circuit, a resistor R1, a resistor R11, a capacitor C1, and a capacitor C3. The main chip U2 is a serial port RS485 conversion chip, comprising a reception input pin DO, a drive input pin DI, a reception output enable pin / RE, a drive output enable pin DE, a reception input and drive output pin A, and a reception input and drive output pin B. The serial port TXD transmission terminal is connected to the input end of the transmission isolation circuit, the output end of the transmission isolation circuit is connected to the input end of the transmission drive amplifier circuit, and the output end of the transmission drive amplifier circuit is connected to the drive input pin DI of the main chip U2 and the enable signal generating circuit. The input end of the generating circuit, the input end of the receiving isolation circuit is connected to the receiving input pin DO of the main chip U2, the output end of the receiving isolation circuit is connected to the input end of the receiving driving amplifier circuit, the serial port RXD receiving end is connected to the output end of the receiving driving amplifier circuit, the output end of the enable signal generating circuit is connected to the receiving output enable pin / RE and the driving output enable pin DE of the main chip U2, the receiving input and driving output pin A of the main chip U2 are connected to the first end of the resistor R1, the second end of the resistor R1 is connected to the isolation power supply VCC_COM1, the receiving input and driving output pin B of the main chip U2 are connected to the first end of the resistor R11, and the second end of the resistor R11 is connected to the isolation power supply VCC_COM1.

2. The circuit for realizing high-speed isolation serial port RS485 using low-speed optical coupler as claimed in claim 1, characterized in that: The transmitting isolation circuit includes an optocoupler U1, a capacitor C2, and a resistor R4. The second pin of the optocoupler U1 is connected to the serial port TXD transmitting end, the fourth pin of the optocoupler U1 is connected to the isolated power supply VCC_COM1, the first end of the resistor R4 is connected to the first pin of the optocoupler U1, the second end of the resistor R4 is connected to the power supply 3.3V, the first end of the capacitor C2 is connected to the first pin of the optocoupler U1, the second end of the capacitor C2 is connected to the power supply 3.3V, and the capacitor C2 is a pull-up filter capacitor for the input signal of the optocoupler U1, which suppresses high-frequency interference signals and improves power quality.

3. The circuit for realizing high-speed isolation serial port RS485 using low-speed optical coupler as claimed in claim 1, characterized in that: The receiving isolation circuit includes an optocoupler U3, a capacitor C4, and a resistor R7. The first end of the resistor R7 is connected to the first pin of the optocoupler U2, the second pin of the optocoupler U3 receives the input end of the isolation circuit, the second end of the resistor R7 is connected to the isolation power supply VCC_COM1, the first end of the capacitor C4 is connected to the first pin of the optocoupler U3, the second end of the capacitor C4 is connected to the isolation power supply VCC_COM1, and the capacitor C4 is a pull-up filter capacitor for the input signal of the optocoupler U3, which suppresses high-frequency interference signals and improves power quality.

4. The circuit for realizing high-speed isolation serial port RS485 using low-speed optical coupler as claimed in claim 1, characterized in that: The transmitting drive amplifier circuit includes a transistor Q1, a resistor R2, and a resistor R5. The base of the transistor Q1 is connected to the input end of the transmitting drive amplifier circuit and the first end of the resistor R5. The emitter of the transistor Q1 and the second end of the resistor R5 are grounded. The collector of the transistor Q1 is connected to the output end of the transmitting drive amplifier circuit and the first end of the resistor R2. The second end of the resistor R2 is connected to the isolated power supply VCC_COM1. The transistor Q1 is used in the transmitting drive amplifier circuit to amplify the output current on the output side of the optocoupler U1 to increase the circuit driving capability.

5. The circuit for realizing high-speed isolation serial port RS485 using low-speed optical coupler as claimed in claim 1, characterized in that: The receiving drive amplifier circuit includes a transistor Q2, a resistor R6, and a resistor R10. The base of the transistor Q2 is connected to the output end of the receiving drive amplifier circuit and the first end of the resistor R10. The emitter of the transistor Q2 and the second end of the resistor R10 are grounded. The collector of the transistor Q2 is connected to the output end of the receiving drive amplifier circuit and the first end of the resistor R6. The second end of the resistor R6 is connected to the power supply 3.3V. The transistor Q2 is used in the receiving drive amplifier circuit to amplify the output current on the output side of the optocoupler U3 to increase the circuit driving capability.

6. The circuit for realizing high-speed isolation serial port RS485 using low-speed optical coupler as claimed in claim 1, characterized in that: The enable signal generating circuit includes a diode D1, a resistor R12, an inverter U4, and a capacitor C5. The cathode of the diode D1 is the input end of the enable signal generating circuit, and is connected to the first end of the resistor R12 and the output end of the sending drive amplifier circuit. The anode of the diode D1 is connected to the input end 1 pin of the inverter U4, the input end 2 pin of the inverter U4, the second end of the resistor R12, and the first end of the capacitor C5. The output end 4 pin of the inverter U4 is connected to the output end of the enable signal generating circuit. The second end of the capacitor C5 is grounded. The inverter U4 performs reverse processing on the input signal.

7. The circuit for realizing high-speed isolation serial port RS485 using low-speed optical coupler as claimed in claim 1, characterized in that: The RS485 circuit is provided with RS485 bus protection devices, semiconductor discharge tube TV1, resistor R3, resistor R9, resettable fuse F1, resettable fuse F2 are RS485 bus protection devices, the first terminal of semiconductor discharge tube TV1 is connected to the second terminal of resistor R3, the first terminal of resistor R3 is connected to the receiving input and driving output pin A of the main chip U2, the second end of resistor R3 is connected to the D1+ terminal of the RS485 bus through the fuse F1, the second terminal of semiconductor discharge tube TV1 is connected to the second end of resistor R9, the first terminal of resistor R9 is connected to the receiving input and driving output pin B of the main chip U2, the second end of resistor R9 is connected to the D1- terminal of the RS485 bus through the fuse F2, the first terminals of capacitor C1 and capacitor C3 are connected to the isolated power supply VCC_COM1, the second terminals of capacitor C1 and capacitor C3 are grounded, capacitor C1 and capacitor C3 are filter capacitors of the isolated power supply VCC_COM1, which are used for high-frequency and low-frequency noise filtering and decoupling, and provide peak current support for the RS485 circuit.

8. The circuit for realizing high-speed isolation serial port RS485 using low-speed optical coupler as claimed in claim 1, characterized in that: The model of the main chip U2 is GM3085.

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