CN110958055B - RS485 communication isolation protection circuit with three-layer protection - Google Patents
RS485 communication isolation protection circuit with three-layer protection Download PDFInfo
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- CN110958055B CN110958055B CN201911251671.4A CN201911251671A CN110958055B CN 110958055 B CN110958055 B CN 110958055B CN 201911251671 A CN201911251671 A CN 201911251671A CN 110958055 B CN110958055 B CN 110958055B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/80—Optical aspects relating to the use of optical transmission for specific applications, not provided for in groups H04B10/03 - H04B10/70, e.g. optical power feeding or optical transmission through water
- H04B10/801—Optical aspects relating to the use of optical transmission for specific applications, not provided for in groups H04B10/03 - H04B10/70, e.g. optical power feeding or optical transmission through water using optical interconnects, e.g. light coupled isolators, circuit board interconnections
- H04B10/802—Optical aspects relating to the use of optical transmission for specific applications, not provided for in groups H04B10/03 - H04B10/70, e.g. optical power feeding or optical transmission through water using optical interconnects, e.g. light coupled isolators, circuit board interconnections for isolation, e.g. using optocouplers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/40—Bus networks
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Abstract
The utility model provides a RS485 communication isolation protection circuit with three-layer protection, relates to gateway class communications facilities, and the purpose is in order to solve the RS485 circuit of commercial gateway product and easily receive thunderbolt or electromagnetic interference, leads to the fragile problem of gateway product. The intelligent control unit is realized by adopting a singlechip and a programmable logic circuit and is used for receiving and sending data through an RS485 bus; the isolation protection unit is realized by adopting a photoelectric isolation module, is positioned between the intelligent control unit and the RS485 drive unit and is used for isolating electric signals on two sides; the open circuit protection unit is connected with the RS485 driving unit and the intelligent control unit and is used for disconnecting the external communication line from the host when the commercial gateway is in a non-working state or a shutdown state; the unloading protection unit is connected with the circuit breaking protection unit and used for unloading electric charges generated by overvoltage or lightning when overvoltage or lightning strikes occur on an external communication line of the business gateway.
Description
Technical Field
The invention relates to gateway communication equipment, in particular to a protection technology of an RS485 communication line.
Background
In the application of the one-card business gateway, the business gateway and a plurality of consumption POS machines form a multi-node complex star-shaped topological network. The RS485 communication mode is a main mode adopted by the network distribution communication of the one-card early-stage product. The RS485 communication has the characteristics of high sensitivity, long distance, good stability, low implementation cost, support of multiple nodes, suitability for half-duplex communication and the like, and is also selected as a communication mode by a plurality of other application systems.
A business gateway product in the earlier stage of the all-purpose card directly adopts a simple RS485 circuit communication mode, is very fragile and safe, and is often large in maintenance amount and high in maintenance cost due to lightning stroke or electromagnetic interference. The reason for analyzing is that the RS485 bus carries out long-distance transmission (more than 1200 meters), and the transmission line is usually exposed outdoors, so overvoltage is easily introduced due to lightning stroke and the like, and the RS485 transceiver has low working voltage (about 5V), has very low self withstand voltage (-7V to + 12V), and can be broken down and damaged once overvoltage is introduced. When strong surge energy appears, the phenomena of burst of the transceiver and burnt circuit board can be even seen, and more seriously, the overvoltage impact can burn any other functional units of the whole equipment sometimes, so that the whole equipment is damaged and cannot be repaired.
Disclosure of Invention
The invention aims to solve the problem that an RS485 circuit of a commercial gateway product is easy to be damaged due to lightning strike or electromagnetic interference, and provides an RS485 communication isolation protection circuit with three layers of protection.
The RS485 communication isolation protection circuit with three layers of protection comprises an intelligent control unit, an isolation protection unit, an RS485 driving unit, a broken circuit protection unit and an unloading protection unit;
in the RS485 communication isolation protection circuit with three layers of protection, main control signals comprise a data sending signal TXDo, a data receiving signal RXDi _ n, a data direction signal DTRo and a circuit breaking control signal M/S _485MODE from an intelligent control unit, and RS485 communication signals POS485p1 and POS485n1 leading to a POS machine assembly.
The intelligent control unit is realized by adopting a single chip microcomputer and a programmable logic circuit and is used for receiving and sending data through an RS485 bus;
the isolation protection unit is realized by adopting a photoelectric isolation module, is positioned between the intelligent control unit and the RS485 drive unit and is used for isolating electric signals on two sides;
the open circuit protection unit is connected with the RS485 driving unit and the intelligent control unit and is used for disconnecting the external communication line from the host when the commercial gateway is in a non-working state or a shutdown state;
the unloading protection unit is connected with the circuit breaking protection unit and used for unloading electric charges generated by overvoltage or lightning when overvoltage or lightning strikes occur on an external communication line of the business gateway.
Further, the photoelectric isolation module comprises two photoelectric coupling devices, and both sides of each photoelectric coupling device are provided with a driving resistor.
Further, the two photoelectric coupling devices are a photoelectric coupling device U1 and a photoelectric coupling device U4 respectively, and the driving resistor comprises a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R13 and a resistor R14;
cathodes of two light emitting diodes at the input side of the photoelectric coupler U1 are used for receiving signals from the intelligent control unit, anodes of the two light emitting diodes are respectively connected with one end of a resistor R6 and one end of a resistor R7, and the other end of the resistor R6 and the other end of the resistor R7 are connected with a 3.3V power supply; emitting electrodes of two triodes at the output side of the photoelectric coupler U1 are connected with a power ground, collecting electrodes of the two triodes are respectively connected with one end of a resistor R4 and one end of a resistor R5, and the other end of the resistor R4, the other end of the resistor R5 and cathodes of two photodiodes at the side are connected with an M5V power supply; the collector electrodes of the two triodes are also simultaneously connected with an RS485 driving unit;
the anode of one light emitting diode at the input side of the photoelectric coupling device U4 is connected with an M5V power supply, the cathode of the light emitting diode is connected with an RS485 driving unit, and the two electrodes of the other light emitting diode at the input side are both suspended; the cathodes of two photodiodes at the output side of the photoelectric coupler U4 are connected with a 5V power supply, the emission sets of the two triodes are connected with a power ground, the collector of one triode at the side is connected with one end of a resistor R13, the common point is used as the input end of a POS machine combined signal, and the collector of the other triode is suspended.
Further, the RS485 driving unit is implemented by using a driving chip of an RS485 protocol, where the driving chip includes a sending chip with a model number of SN75174 and a receiving chip with a model number of SN 75175.
Further, the RS485 driving unit includes a sending chip with model number SN75174, a receiving chip with model number SN75175, a resistor R8, a resistor R10, and a resistor R12;
the E pin, the VBB pin and the DI pin of the sending chip are connected with the isolation protection unit, and the VBB pin and the RO pin of the receiving chip are connected with the isolation protection unit;
the GD pin of the sending chip, the GD pin of the receiving chip and the E pin are connected with a power ground;
with pin B of the transmitting chip connected to the receiving chip simultaneously
The pin, one end of the resistor R8 and one end of the resistor R10 are connected with a switch of the open-circuit protection unit;
the pin A of the sending chip is simultaneously connected with the pin A of the receiving chip, the other end of the resistor R10 and one end of the resistor R12, and the connection point is also used for connecting a switch of the open-circuit protection unit;
the other end of the resistor R8 is connected with an M5V power supply, and the other end of the resistor R12 is connected with a power ground;
and the two ends of the resistor R10 are also simultaneously connected with an open-circuit protection unit.
Furthermore, the open circuit protection unit comprises a relay and a driving circuit thereof, and a control signal input end of the relay is connected with an open circuit control signal output end of the intelligent control unit.
Further, the driving circuit comprises a resistor R1, a resistor R2, a resistor R3, a capacitor C1, a capacitor C2, a capacitor C3, a triode Q1, a field effect transistor Q2 and a diode D1;
the anode of the diode D1 is simultaneously connected with the negative input end of the relay coil and the power ground, and the cathode of the diode D1 is simultaneously connected with the positive input end of the relay coil, one end of the capacitor C1 and the collector of the triode Q1;
the other end of the capacitor C1 and an emitting electrode of the triode Q1 are both connected with a 5V power supply;
the base electrode of the triode Q1 is simultaneously connected with one end of the capacitor C2, one end of the capacitor C3 and one end of the resistor R2; the other end of the capacitor C2 and the other end of the capacitor C3 are connected with a power ground;
the other end of the resistor R2 is simultaneously connected with one end of the resistor R1 and the source electrode of the field effect transistor Q2, and the other end of the resistor R1 is connected with a 5V power supply;
the drain electrode of the field effect transistor Q2 is connected with a power ground, the grid electrode of the field effect transistor Q2 is connected with one end of the resistor R3, and the connection point is used as the input end of a circuit breaking control signal;
the other end of the resistor R3 is connected with a 5V power supply.
Further, the unloading protection unit is realized by a three-pole lightning protection circuit.
Further, the unloading protection unit comprises a resistor R9, a resistor R11, a discharge tube G1 and two TVS tubes;
one end of the resistor R9 and one end of the resistor R11 are connected with a switch of the open-circuit protection unit, the other end of the resistor R9 and the other end of the resistor R11 are respectively connected with two ends of the discharge tube G1, and the two ends of the discharge tube G1 are also used for carrying out RS485 communication with the POS machine combination; the cathode of one TVS tube is connected with a power ground, the anode of the other TVS tube is connected with the anode of the other TVS tube, and the cathode of the other TVS tube is connected with a switch of the circuit breaking protection unit.
The RS485 communication isolation protection circuit with three layers of protection mainly comprises an intelligent control unit, an isolation protection unit, an RS485 driving unit, a circuit breaking protection unit and an unloading protection unit. The isolation protection unit, the open circuit protection unit and the unloading protection unit form three-layer protection of the business gateway.
The intelligent control unit mainly comprises a task processing core consisting of a high-performance singlechip and a programmable logic circuit, wherein one of important tasks is to receive and send data on an RS485 line, detect whether own RS485 communication data is reliable or not and whether a communication line is normal or not, and timely give an alarm and process a decision.
The isolation protection unit mainly comprises a high-performance photoelectric isolation module, which is the first layer of protection measure of the invention. The isolation protection unit has the functions of: control signals related in the communication process and signals received and sent by the intelligent control unit and the RS485 driving unit are transmitted through photoelectric conversion. The communication signal is divided into a front end and a back end, and the front end and the back end adopt different power supplies for power supply. The isolation protection unit realizes the principle isolation of electrical signals in RS485 communication of the commercial gateway, can reduce other interference to the minimum in addition to effective communication data transmission, realizes circuit isolation of signals of the intelligent control unit and a rear circuit, and reduces the electrical damage of the rear circuit to the front circuit to the minimum.
The RS485 driving unit mainly comprises a driving chip of an RS485 protocol, wherein the driving chip comprises an RS485 sending chip and an RS485 receiving chip which are communication core chips of an RS485 hardware circuit and are responsible for the interconversion of an RS485 differential signal and a digital logic signal. The transmitting part of the RS485 driving unit is controlled by the intelligent control unit, high-level transmission is enabled, and the receiving part of the RS485 driving unit is always in a receiving state.
The open circuit protection unit of the present invention is the second layer of protection of the present invention. The functions of the circuit breaking protection unit are as follows: when the commercial gateway is in a non-working state or a shutdown state, the external communication line is disconnected with the commercial gateway host, so that the host can be prevented from being damaged by the external line when the external line is subjected to lightning or electrostatic overvoltage interference. When the gateway is shut down, the external circuit is positioned on the normally closed circuit of the relay and is completely disconnected with the host circuit, and a discharge circuit cannot be formed when lightning stroke or electrostatic overvoltage interference occurs, so that the safety of the business gateway host can be ensured. When the computer is started and is in a non-working state, the circuit breaking protection unit is controlled by the intelligent module unit to disconnect the external communication circuit from the host, and the safety of the host is also ensured.
The unloading protection unit is the third layer of protection measure of the invention, can be realized by adopting a simplified three-level lightning protection circuit, is customized for the self characteristics of the communication of the commercial gateway and is an improved lightning protection circuit on the premise of ensuring the communication quality. The function of the circuit is that when the external communication line is over-voltage or lightning strike, the circuit unloads the charges through three times of voltage reduction, and the communication line is protected from self safety under the bearing capacity.
The RS485 communication isolation protection circuit with three layers of protection has the advantages that:
1. the protection is multilayer, and the level is clear, and the protection level is high. The protection layer by layer can make the protection become safer and more effective.
2. The photoelectric isolation can effectively protect the intelligent control unit from being damaged, not only can protect the safety of the intelligent control unit, but also can greatly reduce the maintenance cost.
3. The open circuit protection can ensure that the commercial gateway is in spatial isolation with an external circuit in most of non-working time, thereby greatly improving the protection effect.
4. Through the improved three-level lightning protection measures, the method is more targeted for the business gateway and has timeliness.
The invention can be suitable for various electronic devices using RS485 communication, can effectively prevent lightning stroke and static overvoltage interference, and effectively protects a communication circuit from being damaged.
Drawings
Fig. 1 is a block diagram of an RS485 communication isolation protection circuit with three layers of protection according to an embodiment of the present invention; wherein, (1) represents M/S485 MODE signal, (2) represents DTRo signal, (3) represents TXDO signal, (4) represents RXDi- _ n signal, (5) represents POS485p1 signal, and (6) represents POS485n1 signal;
fig. 2 is a schematic circuit structure diagram of an RS485 communication isolation protection circuit with three layers of protection according to an embodiment of the present invention.
Detailed Description
The first embodiment is as follows: the present embodiment will be described with reference to fig. 1 and 2. The embodiment mainly realizes the protection of the communication circuit in the business gateway. As shown in figure 1, the intelligent control unit is combined with the POS machine, data communication needs to be achieved through the RS485 driving unit, communication signals need to be isolated through the first layer of photoelectric isolation between the intelligent control unit and the RS485 driving unit, and electric signals of the two parts are almost completely isolated. The POS machine combination and the RS485 driving unit are connected through a third layer unloading protection unit formed by a three-level lightning protection circuit and a second layer relay. Through three layers of protection measures, the gateway equipment can be well protected from being damaged by thunder and lightning and electrostatic interference.
In this embodiment, the first layer of isolation protection is realized by the optoelectronic isolation module in fig. 2, which mainly comprises two optoelectronic coupling devices U1 and U4 and a driving resistor, and the communication rate is about 20 khz. The resistance of the driving resistor is selected to minimize the delay and distortion of the communication signal.
The two photoelectric coupling devices are a photoelectric coupling device U1 and a photoelectric coupling device U4 respectively, and the driving resistor comprises a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R13 and a resistor R14;
cathodes of two light emitting diodes at the input side of the photoelectric coupling device U1 are used for receiving DIR from the intelligent control unit O Signal sum TXD O The anodes of the two light emitting diodes are respectively connected with one end of a resistor R6 and one end of a resistor R7, and the other ends of the resistor R6 and the resistor R7 are connected with a 3.3V power supply; two and three of the output sides of the photoelectric coupling device U1The emitting electrodes of the polar tubes are connected with a power ground, the collecting electrodes of the two polar tubes are respectively connected with one end of a resistor R4 and one end of a resistor R5, and the other end of the resistor R4, the other end of the resistor R5 and the cathodes of the two photodiodes at the side are all connected with an M5V power supply; the collector electrodes of the two triodes are also simultaneously connected with an RS485 driving unit;
the anode of one light emitting diode at the input side of the photoelectric coupler U4 is connected with an M5V power supply, the cathode of the light emitting diode is connected with an RS485 driving unit, and the two poles of the other light emitting diode at the input side are both suspended; the cathodes of two photodiodes at the output side of the photoelectric coupler U4 are connected with a 5V power supply, the emission sets of the two triodes are connected with a power ground, the collector of one triode at the side is connected with one end of a resistor R13, the common point is used as an input end for receiving RXDi _ n signals from the POS machine assembly, and the collector of the other triode is suspended.
In the embodiment, the RS485 driving unit in fig. 2 is used for converting the RS485 communication electrical signals. The RS485 driver chip adopts a driver chip with the model number of SN75174 as a data sending driver chip, and adopts a driver chip with the model number of SN75175 as a data receiving driver chip. The two chips support 4 paths of RS485 communication respectively. When data is transmitted, whether the transmitting chip SN75174 transmits data is controlled by the IO signal of the intelligent control unit, and the receiving chip SN75175 receives data and is set to be in a normal receiving mode. The receiving and sending processes are intelligently controlled by a program embedded in the intelligent control unit.
The RS485 driving unit specifically comprises a sending chip with the model number of SN75174, a receiving chip with the model number of SN75175, a resistor R8, a resistor R10 and a resistor R12;
the E pin, the VBB pin and the DI pin of the sending chip are connected with the isolation protection unit, and the VBB pin and the RO pin of the receiving chip are connected with the isolation protection unit;
the GD pin of the sending chip, the GD pin of the receiving chip and the E pin are connected with a power ground;
with pin B of the transmitting chip connected to the receiving chip simultaneously
The pin, one end of the resistor R8 and one end of the resistor R10 are connected with a switch of the open-circuit protection unit;
the pin A of the sending chip is simultaneously connected with the pin A of the receiving chip, the other end of the resistor R10 and one end of the resistor R12, and the connection point is also used for connecting a switch of the open-circuit protection unit;
the other end of the resistor R8 is connected with an M5V power supply, and the other end of the resistor R12 is connected with a power ground;
the two ends of the resistor R10 are also simultaneously connected with an open-circuit protection unit.
The second layer of isolation protection is implemented by the open circuit protection unit in fig. 2 in this embodiment. The circuit breaking protection unit comprises a relay and a driving circuit thereof, and the control signal input end of the relay is connected with the circuit breaking control signal output end of the intelligent control unit. The driving circuit comprises a resistor R1, a resistor R2, a resistor R3, a capacitor C1, a capacitor C2, a capacitor C3, a triode Q1, a field effect tube Q2 and a diode D1;
the anode of the diode D1 is simultaneously connected with the negative input end of the relay coil and the power ground, and the cathode of the diode D1 is simultaneously connected with the positive input end of the relay coil, one end of the capacitor C1 and the collector of the triode Q1;
the other end of the capacitor C1 and the emitting electrode of the triode Q1 are both connected with a 5V power supply;
the base electrode of the triode Q1 is simultaneously connected with one end of the capacitor C2, one end of the capacitor C3 and one end of the resistor R2; the other end of the capacitor C2 and the other end of the capacitor C3 are connected with a power ground;
the other end of the resistor R2 is simultaneously connected with one end of the resistor R1 and the source electrode of the field effect transistor Q2, and the other end of the resistor R1 is connected with a 5V power supply;
the drain electrode of the field effect transistor Q2 is connected with a power ground, the grid electrode of the field effect transistor Q2 is connected with one end of the resistor R3, and the connection point is used as the input end of a circuit breaking control signal M/S485 MODE;
the other end of the resistor R3 is connected with a 5V power supply.
When the mobile terminal is started and does not work, the intelligent control unit sends out a control signal to control the relay to disconnect the communication line, so that the external communication line is disconnected with the host of the commercial gateway; under the shutdown state, the external communication line can be disconnected with the commercial gateway host by means of the normally open contact of the relay. The driving circuit of the relay realizes the stable control of the relay through the diode Q1 and the field effect transistor Q2, and meanwhile, the leakage diode D1 is arranged, so that the minimum interference of the closing of the relay on a main circuit can be ensured.
The third layer of isolation protection is realized by the unloading protection unit in fig. 2 in the present embodiment. The unloading protection unit comprises a resistor R9, a resistor R11, a discharge tube G1 and two TVS tubes;
one end of the resistor R9 and one end of the resistor R11 are connected with a switch of the open-circuit protection unit, the other end of the resistor R9 and the other end of the resistor R11 are respectively connected with two ends of the discharge tube G1, and the two ends of the discharge tube G1 are also used for carrying out RS485 communication with the POS machine combination; the cathode of one TVS tube is connected with a power ground, the anode of the other TVS tube is connected with the anode of the other TVS tube, and the cathode of the other TVS tube is connected with a switch of the circuit breaking protection unit.
The unloading protection unit can protect the self from being damaged by lightning stroke and static overvoltage to a certain extent as long as the unloading protection unit is connected to the safe and reliable ground. When lightning stroke or electrostatic overvoltage is applied to an external communication circuit, common mode rejection is realized through a discharge tube G1 to finish first-stage overvoltage prevention, and the overvoltage is unloaded to the ground; the second-stage overvoltage prevention can be realized through the two current-limiting resistors; and finally, third-stage overvoltage prevention is realized through a voltage limiting TVS tube. In addition, the discharge tube is placed behind the open-circuit protection unit, and the function of protecting other external circuit equipment after shutdown can be achieved.
In addition, the embodiment also adopts another isolated power supply to independently supply power for the communication external circuit, and not only the signal isolation, but also the power supply is isolated. The front end of the communication adopts the working voltage of the gateway host to supply power of 3.3V, and the rear end adopts an independent power supply of 5V to supply power. The power supply and the signal are isolated simultaneously, so that the isolation protection effect is better, the isolation protection is in the true sense, and secondary damage to the main control circuit caused by lightning stroke or overvoltage interference through the isolation power supply is avoided.
Claims (7)
1. An RS485 communication isolation protection circuit with three-layer protection is characterized by comprising an intelligent control unit, an isolation protection unit, an RS485 drive unit, a disconnection protection unit and an unloading protection unit;
the intelligent control unit is realized by adopting a single chip microcomputer and a programmable logic circuit and is used for receiving and sending data through an RS485 bus;
the isolation protection unit is realized by adopting a photoelectric isolation module, is positioned between the intelligent control unit and the RS485 driving unit and is used for isolating electric signals on two sides;
the open circuit protection unit is connected with the RS485 driving unit and the intelligent control unit and is used for disconnecting the external communication line from the host when the commercial gateway is in a non-working state or a shutdown state;
the unloading protection unit is connected with the open circuit protection unit and is used for unloading electric charges generated by overvoltage or lightning stroke when the overvoltage or the lightning stroke occurs on an external communication line of the business gateway;
the photoelectric isolation module comprises two photoelectric coupling devices, and both sides of each photoelectric coupling device are provided with driving resistors;
the two photoelectric coupling devices are a photoelectric coupling device U1 and a photoelectric coupling device U4 respectively, and the driving resistor comprises a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R13 and a resistor R14;
cathodes of two light emitting diodes at the input side of the photoelectric coupler U1 are used for receiving signals from the intelligent control unit, anodes of the two light emitting diodes are respectively connected with one end of a resistor R6 and one end of a resistor R7, and the other end of the resistor R6 and the other end of the resistor R7 are connected with a 3.3V power supply; emitting electrodes of two triodes at the output side of the photoelectric coupler U1 are connected with a power ground, collecting electrodes of the two triodes are respectively connected with one end of a resistor R4 and one end of a resistor R5, and the other end of the resistor R4, the other end of the resistor R5 and cathodes of two photodiodes at the side are connected with an M5V power supply; the collecting electrodes of the two triodes are also simultaneously connected with an RS485 driving unit;
the anode of one light emitting diode at the input side of the photoelectric coupler U4 is connected with an M5V power supply, the cathode of the light emitting diode is connected with an RS485 driving unit, and the two poles of the other light emitting diode at the input side are both suspended; the cathodes of two photodiodes at the output side of the optoelectronic coupler U4 are both connected with a 5V power supply, the emission collectors of the two triodes are both connected with a power ground, the collector of one triode at the side is connected with one end of a resistor R13, the common point is also used for receiving a signal from a POS machine combination, and the collector of the other triode is suspended.
2. The RS485 communication isolation protection circuit with three-layer protection according to claim 1, wherein the RS485 driving unit is implemented by a driving chip of RS485 protocol, and the driving chip comprises a sending chip with model SN75174 and a receiving chip with model SN 75175.
3. The RS485 communication isolation protection circuit with three-layer protection according to claim 2, wherein the RS485 driving unit comprises a sending chip with model number SN75174, a receiving chip with model number SN75175, a resistor R8, a resistor R10, and a resistor R12;
the E pin, the VBB pin and the DI pin of the sending chip are connected with the isolation protection unit, and the VBB pin and the RO pin of the receiving chip are connected with the isolation protection unit;
the GD pin of the sending chip, the GD pin of the receiving chip and the E pin are connected with a power ground;
with pin B of the transmitting chip connected to the receiving chip simultaneously
The pin, one end of the resistor R8 and one end of the resistor R10 are connected with the switch of the open-circuit protection unit;
the pin A of the sending chip is simultaneously connected with the pin A of the receiving chip, the other end of the resistor R10 and one end of the resistor R12, and the connection point is also used for connecting a switch of the open-circuit protection unit;
the other end of the resistor R8 is connected with an M5V power supply, and the other end of the resistor R12 is connected with a power ground;
the two ends of the resistor R10 are also simultaneously connected with an open-circuit protection unit.
4. The RS485 communication isolation protection circuit with three-layer protection according to claim 1, wherein the open circuit protection unit comprises a relay and a driving circuit thereof, and a control signal input end of the relay is connected with an open circuit control signal output end of the intelligent control unit.
5. The RS485 communication isolation protection circuit with three-layer protection according to claim 4, wherein the driving circuit comprises a resistor R1, a resistor R2, a resistor R3, a capacitor C1, a capacitor C2, a capacitor C3, a triode Q1, a field effect transistor Q2, and a diode D1;
the anode of the diode D1 is simultaneously connected with the negative input end of the relay coil and the power ground, and the cathode of the diode D1 is simultaneously connected with the positive input end of the relay coil, one end of the capacitor C1 and the collector of the triode Q1;
the other end of the capacitor C1 and an emitting electrode of the triode Q1 are both connected with a 5V power supply;
the base electrode of the triode Q1 is simultaneously connected with one end of the capacitor C2, one end of the capacitor C3 and one end of the resistor R2; the other end of the capacitor C2 and the other end of the capacitor C3 are connected with a power ground;
the other end of the resistor R2 is simultaneously connected with one end of the resistor R1 and the source electrode of the field effect transistor Q2, and the other end of the resistor R1 is connected with a 5V power supply;
the drain electrode of the field effect transistor Q2 is connected with a power ground, the grid electrode of the field effect transistor Q2 is connected with one end of the resistor R3, and the connection point is used as the input end of an open circuit control signal;
the other end of the resistor R3 is connected with a 5V power supply.
6. The RS485 communication isolation protection circuit with three-layer protection according to claim 1, wherein the unloading protection unit is implemented by a three-pole lightning protection circuit.
7. The RS485 communication isolation protection circuit with three-layer protection according to claim 1, wherein the unloading protection unit comprises a resistor R9, a resistor R11, a discharge tube G1, and two TVS tubes;
one end of the resistor R9 and one end of the resistor R11 are connected with a switch of the open-circuit protection unit, the other end of the resistor R9 and the other end of the resistor R11 are respectively connected with two ends of the discharge tube G1, and the two ends of the discharge tube G1 are also used for carrying out RS485 communication with the POS machine combination; the cathode of one TVS tube is connected with a power ground, the anode of the other TVS tube is connected with the anode of the other TVS tube, and the cathode of the other TVS tube is connected with a switch of the circuit breaking protection unit.
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| CN201911251671.4A CN110958055B (en) | 2019-12-09 | 2019-12-09 | RS485 communication isolation protection circuit with three-layer protection |
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| CN201911251671.4A CN110958055B (en) | 2019-12-09 | 2019-12-09 | RS485 communication isolation protection circuit with three-layer protection |
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| CN110958055B true CN110958055B (en) | 2022-11-15 |
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| CN201911251671.4A Active CN110958055B (en) | 2019-12-09 | 2019-12-09 | RS485 communication isolation protection circuit with three-layer protection |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN201402965Y (en) * | 2009-04-28 | 2010-02-10 | 苏州工业园区新宏博通讯科技有限公司 | Single-phase intelligent electricity utilization protecting device |
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| CA2966313A1 (en) * | 2013-10-31 | 2015-05-07 | Innosys, Inc. | Fluorescent lamp replacement led protection |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN201402965Y (en) * | 2009-04-28 | 2010-02-10 | 苏州工业园区新宏博通讯科技有限公司 | Single-phase intelligent electricity utilization protecting device |
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