RS232 serial communication interface intelligent identification and switching circuit

Abstract

The invention discloses an RS232 serial communication interface intelligent identification and switching circuit which comprises a switch matrix, the input end of the switch matrix is used for being connected with opposite end equipment, and the output end of the switch matrix is connected with a first detection circuit and a second detection circuit; the input end of the first detection circuit is connected with the switch matrix, and the output end of the first detection circuit is connected with the processor module; the input end of the second detection circuit is connected with the switch matrix, and the output end of the second detection circuit is connected with the processor module; and the input end of the RS232 interface is connected with the switch matrix, and the RS232 interface comprises a transmitter TXD end, a receiver RXD end and a ground GND end. The RS232 serial communication interface intelligent identification and switching circuit provided by the invention has the characteristics that a signal line is intelligently switched into a correct connection method, equipment is protected from being damaged, manual cable connection change is saved, and RS232 serial interface communication is effectively established.

Description

Technical Field

[0001] The present invention belongs to the field of integrated circuits. More specifically, the present invention relates to an intelligent recognition and switching circuit for RS232 serial communication interfaces. Background Art

[0002] The standard RS232 serial communication interface initially adopted a 25-pin DB25 connector, with the signal content of each pin of the connector specified, and the levels of various signals also specified. Later, IBM's PC simplified RS232 into a DB9 connector, which thus became a de facto standard. The RS232 interface for industrial control generally only uses three wires, namely RXD (receive), TXD (transmit), and GND (ground), to achieve simple full-duplex serial communication. Its connector does not necessarily use a DB9 connector but may use a connector with fewer pins or even only 3 pins.

[0003] When users self-make a simple three-wire RS232 serial communication cable, it is easy to mistake RXD and TXD, that is, the signal connections between two devices are incorrect and RS232 serial communication cannot be carried out.

[0004] In the prior art, such as Figure 2 , the correct connection method of the RS232 interface between two devices should be that the sending end of device A is connected to the receiving end of device B, and the receiving end of device A is connected to the sending end of device B, and the grounds of the two devices are connected together.

[0005] Figure 3 Shown is a wiring diagram for a common error in the RS232 interface between two devices. When the RS232 interface connection method between two devices is such that the grounds are connected together, and the sending end of device A is connected to the sending end of device B, and the receiving end of device A is connected to the receiving end of device B, RS232 serial communication cannot be carried out between the two devices, and the cable connection needs to be manually changed to establish RS232 serial communication.

[0006] When the RS232 interface connection method between two devices is incorrect and the sending end of a certain device is connected to the ground, not only can RS232 serial communication not be carried out, but device damage may even occur. Figure 4 Shown is an example wiring diagram for a serious error in the RS232 interface between two devices. If there are other interface circuits that make the two devices share a common ground, the transmitter of the RS232 interface of device A may be damaged.

[0007] Therefore, it is necessary to develop an intelligent recognition and switching circuit for RS232 serial communication interfaces, which can intelligently switch the signal lines to the correct connection method and effectively establish RS232 serial interface communication. Summary of the Invention

[0008] An object of the present invention is to solve at least the above problems and / or deficiencies and provide at least the advantages described hereinafter.

[0009] To achieve these objects and other advantages of the present invention, there is provided an intelligent identification and switching circuit for an RS232 serial communication interface, including:

[0010] A switch matrix, whose input end is used to connect to a peer device, and the output end of the switch matrix is connected to a first detection circuit and a second detection circuit;

[0011] A first detection circuit, whose input end is connected to the switch matrix, and the output end of the first detection circuit is connected to a processor module. When a current signal passes through the first detection circuit and sends a status signal one to the processor, when the processor module detects that the status signal one is at a low level, the processor determines that the port signal is the RXD signal line, and the first detection is completed;

[0012] A second detection circuit, whose input end is connected to the switch matrix, and the output end of the second detection circuit is connected to a processor module. When a current signal passes through the second detection circuit and sends a status signal two to the processor, when the processor module detects that the status signal two is: a current signal with a voltage range of 1 / 3×Vcc to 1 / 2×Vcc, the processor determines that the port signal is the GND signal line, and the second detection is completed;

[0013] By determining that the port signal is the RXD signal line through the first detection circuit, and the second detection circuit determines that the port signals are the GND signal line and the TXD signal line respectively. At this time, the processor sends a control signal to the switch matrix, and the switch matrix connects the three signal lines with the measured results to the transmitter TXD end, the receiver RXD end and the ground GND end corresponding to the RS232 interface respectively, effectively establishing RS232 serial interface communication.

[0014] Preferably, wherein, the first detection circuit includes:

[0015] A first optocoupler V1, the positive electrode of whose diode is connected to the output end of the switch matrix, and a resistor R1 is provided on the connection line. The emitter of the triode of the first optocoupler V1 is connected to the ground wire, the collector of the triode of the first optocoupler V1 is connected to the VCC end, and a resistor R3 is provided on the connection line. The collector of the triode of the first optocoupler V1 is connected to the signal input end of the processor module, and outputs the status signal one;

[0016] A second optocoupler V2, the positive electrode of whose diode is connected to the output end of the switch matrix, and a resistor R2 is provided on the connection line. The emitter of the triode of the second optocoupler V2 is connected to the ground wire, and the collector of the triode of the second optocoupler V2 is connected to the signal input end of the processor module, and outputs the status signal one.

[0017] Preferably, the second detection circuit includes:

[0018] A first test circuit, on which a resistor R5 is provided, one end of the resistor R5 is connected to the ground wire, and the other end of the resistor R5 is connected to the signal input end of the processor module, outputting a second status signal;

[0019] A second test circuit, on which a resistor R4 is provided, and the resistor R4 is connected to the VCC terminal.

[0020] Preferably, the method includes the following steps:

[0021] Step 1:

[0022] Connect the output ends of any two of the three unknown signal lines of the peer device to the first detection circuit, the positive poles of the diodes of the first optocoupler V1 and the positive poles of the diodes of the second optocoupler V2,

[0023] Perform three tests, respectively testing a certain combination between AB, AC, and BC, which can make the diode of the first optocoupler V1 emit light normally and the collector and emitter of the triode conduct saturatedly, or the diode of the second optocoupler V2 emit light normally and the collector and emitter of the triode conduct saturatedly;

[0024] At this time, for the first status signal received by the processor module, the two lines that can make the first status signal output a low level are the TXD signal line or the GND line, and the other one is the RXD signal line.

[0025] Step 2:

[0026] Connect the RXD signal line measured in Step 1 among the three unknown signal lines of the peer device to the second test circuit of the second detection circuit, and then connect the two unknown signal lines of the peer device to the first test circuit respectively for two tests;

[0027] At this time, in the second status signal received by the processor module, when the voltage range is 1 / 3×Vcc~1 / 2×Vcc, it is confirmed that the measured line is the GND line;

[0028] Step 3:

[0029] Determine that the port signal is the RXD signal line through the first detection circuit, and determine that the port signals of the second detection circuit are the GND signal line and the TXD signal line respectively. At this time, the processor sends a control signal to the switch matrix, and the switch matrix connects the three signal lines with the measured results to the corresponding transmitter TXD terminal, receiver RXD terminal, and ground GND terminal respectively, effectively establishing RS232 serial interface communication.

[0030] The present invention has at least the following beneficial effects:

[0031] The present invention provides an intelligent identification and switching circuit for an RS232 serial communication interface, which has the characteristics of intelligently switching signal lines to the correct connection method, protecting the device from damage, saving manual cable connection changes, and effectively establishing RS232 serial interface communication.

[0032] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Brief Description of the Drawings

[0033] Figure 1 It is the schematic diagram of the intelligent identification and switching circuit for the RS232 serial communication interface of the present invention;

[0034] Figure 2 It is the correct wiring diagram of the RS232 interface between two devices in the prior art;

[0035] Figure 3 It is the wiring diagram of the RS232 interface between two devices in the prior art with a general error;

[0036] Figure 4 It is the wiring diagram of the RS232 interface between two devices in the prior art with a serious error;

[0037] Figure 5 It is the principle analysis diagram of the TXD signal line and GND line identification circuit for the RS232 serial communication interface of the present invention (when the GND line is switched to the second detection circuit);

[0038] Figure 6 It is the principle analysis diagram of the TXD signal line and GND line identification circuit for the RS232 serial communication interface of the present invention (when the TXD signal line is switched to the second detection circuit). Detailed Description of the Preferred Embodiments

[0039] The following further describes the present invention in detail with reference to the drawings, so that those skilled in the art can implement it according to the description in the specification.

[0040] It should be understood that the terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0041] It should be noted that in the description of the present invention, the orientation or positional relationship indicated by the terms is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0042] In the description of the present invention, unless otherwise clearly defined and limited, terms such as "installation", "equipped with", "sheathed / connected", "connection", etc. shall be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection, it can be a mechanical connection, an electrical connection, it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0043] In addition, in the present invention, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature can be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature can be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0044] Figure 1-6 An intelligent identification and switching circuit for an RS232 serial communication interface according to the present invention is shown, including:

[0045] A switch matrix, whose input end is used to connect to a peer device, and the output end of the switch matrix is connected with a first detection circuit and a second detection circuit;

[0046] A first detection circuit, whose input end is connected to the switch matrix, and the output end of the first detection circuit is connected to a processor module. When a current signal passes through the first detection circuit and sends a first status signal to the processor, when the processor module detects that the first status signal is at a low level, the processor determines that the port signal is the RXD signal line and completes the first detection;

[0047] A second detection circuit, whose input end is connected to the switch matrix, and the output end of the second detection circuit is connected to a processor module. When a current signal passes through the second detection circuit and sends a second status signal to the processor, when the processor module detects that the second status signal is a current signal with a voltage range of 1 / 3×Vcc to 1 / 2×Vcc, the processor determines that the port signal is the GND signal line and completes the second detection;

[0048] The first detection circuit determines that the port signal is the RXD signal line, and the second detection circuit determines that the port signals are the GND signal line and the TXD signal line respectively. At this time, the processor sends a control signal to the switch matrix, and the switch matrix connects the three signal lines with the measured results to the transmitter TXD terminal, the receiver RXD terminal, and the ground GND terminal corresponding to the RS232 interface respectively, effectively establishing RS232 serial interface communication.

[0049] Working principle:

[0050] Generally, an RS232 interface consists of a transmitter and a receiver.

[0051] The voltage range and logic definition of the RS232 serial communication interface level standard are as follows:

[0052] For the RS232 level standard, the logic 1 level is -3V to -15V, and the logic 0 level is +3V to +15V. That is, when the transmitter TXD terminal sends logic 1, the voltage to the GND terminal is -3V to -15V, and when the transmitter TXD terminal sends logic 0, the voltage to the GND terminal is +3V to +15V;

[0053] When there is no external input at the receiver RXD terminal of the RS232 serial communication interface, the input voltage to the GND terminal is about 0V, and there is a pull-down resistor from the internal input RXD terminal of the receiver to the GND terminal;

[0054] According to the characteristics of the transmitter end and the receiver end of the above RS232 serial communication interface, a detection circuit can be designed to identify them, and an intelligent identification and switching circuit for the RS232 serial communication interface of the present invention;

[0055] As Figure 2 It can be seen from that the correct docking method is:

[0056] The transmitter TXD terminal of device A is docked to the receiver RXD terminal of device B, the receiver RXD terminal of device A is docked to the transmitter TXD terminal of device B, and the ground GND terminals of the two devices are connected;

[0057] The present invention uses a detection circuit to perform circuit detection on the three serial port signal lines from the peer device through the first detection circuit 1, the second detection circuit 2, the processor module, and the switch matrix. The specific steps are as follows (the peer device A includes three unknown ports A, B, and C to be detected):

[0058] Step 1:

[0059] Switch the output terminals of any two of the three unknown signal lines of the peer device to the first detection circuit, the anode of the diode of the first optocoupler V1 and the anode of the diode of the second optocoupler V2,

[0060] Conduct three tests to test a certain combination between AB, AC, and BC respectively, which can make the diode of the first optocoupler V1 emit light normally and the collector and emitter of the triode conduct saturatedly, or make the diode of the second optocoupler V2 emit light normally and the collector and emitter of the triode conduct saturatedly;

[0061] At this time, for the first status signal received by the processor module, the two wires that can output a low level for the status signal one are the TXD signal wire or the GND wire, and the other one is the RXD signal wire.

[0062] Step Two:

[0063] Connect the RXD signal wire measured in Step One among the three unknown signal wires of the peer device to the test circuit two (G terminal) of the second detection circuit, and then connect the two unknown signal wires of the peer device to the test circuit one (F terminal) respectively for two tests;

[0064] Among the second status signals received by the processor module at this time, when the voltage range is 1 / 3×Vcc~1 / 2×Vcc, it is confirmed that the measured wire is the GND wire;

[0065] Step Three:

[0066] Determine that the port signal is the RXD signal wire through the first detection circuit, and determine that the port signals of the second detection circuit are the GND signal wire and the TXD signal wire respectively. At this time, the processor sends a control signal to the switch matrix, and the switch matrix connects the three signal wires of device A with the measured results to the corresponding transmitter TXD terminal, receiver RXD terminal, and ground GND terminal respectively to effectively establish RS232 serial interface communication;

[0067] Among them, a switch matrix is constructed by multiple controllable switches, which can switch the three signal wires from the peer device to the first detection circuit 1, or switch to the second detection circuit 2, or switch to the RS232 serial communication interface of this device, the transmitter TXD terminal, the receiver RXD terminal, and the GND terminal. For the convenience of explaining the working principle, the schematic diagram of the intelligent identification and switching circuit of the RS232 serial communication interface is simplified here, and the switch matrix is not drawn in detail.

[0068] In the above solution, the first detection circuit 1 includes:

[0069] The first optocoupler V1, the positive pole of its diode is connected to the output terminal of the switch matrix, and a resistor R1 is arranged on the connection line. The emitter of the triode of the first optocoupler V1 is connected to the ground wire, the collector of the triode of the first optocoupler V1 is connected to the VCC terminal, and a resistor R3 is arranged on the connection line. The collector of the triode of the first optocoupler V1 is connected to the signal input terminal of the processor module to output the first status signal;

[0070] The second optocoupler V2, the positive electrode of its diode is connected to the output terminal (D terminal) of the switch matrix, and a resistor R2 is provided on the connection line. The emitter of the triode of the second optocoupler V2 is connected to the ground wire, and the collector of the triode of the second optocoupler V2 is connected to the signal input terminal of the processor module, outputting a first status signal.

[0071] Working principle:

[0072] The working process of the first detection circuit 1 is as follows:

[0073] The processor module controls the switch matrix to switch any two of the three signal lines from the peer device to the first detection circuit 1 for three tests to respectively test whether a certain combination can make the first detection circuit 1 emit light normally, thereby enabling the first detection circuit 1 to be saturated and conduct.

[0074] (1) When the transmitter TXD terminal and the ground GND terminal of the RS232 serial communication interface from the peer device are respectively connected to the positive electrode (E terminal) of the diode of the first optocoupler V1 and the positive electrode (D terminal) of the diode of the second optocoupler V2 of the detection circuit, and when the resistance values of the resistors R1 and R2 are appropriate:

[0075] ① The positive voltage of the transmitter TXD terminal with respect to the GND terminal causes current to pass through the resistor R2 and the diode of the second optocoupler V2. The diode of the second optocoupler V2 emits light normally, thereby enabling the collector and emitter of the photosensitive triode of the second optocoupler V2 to be saturated and conduct, and the first status signal outputs a low level.

[0076] ② The negative voltage of the transmitter TXD terminal with respect to the GND terminal causes current to pass through the resistor R1 and the diode of the first optocoupler V1. The diode of the first optocoupler V1 emits light normally, thereby enabling the collector and emitter of the photosensitive triode of the first optocoupler V1 to be saturated and conduct, and the first status signal outputs a low level.

[0077] (2) When the receiver RXD terminal and the ground GND terminal of the RS232 serial communication interface from the peer device are respectively connected to the positive electrode (E terminal) of the diode of the first optocoupler V1 and the positive electrode (D terminal) of the diode of the second optocoupler V2 of the detection circuit, since the voltage of the RXD terminal with respect to the GND terminal is about 0V, the diodes of both the first optocoupler V1 and the second optocoupler V2 do not emit light, and the collectors and emitters of the photosensitive triodes of the first optocoupler V1 and the second optocoupler V2 are cut off and non-conductive, and the first status signal outputs a high level.

[0078] (3) When the transmitter TXD terminal and the receiver RXD terminal of the RS232 serial communication interface from the peer device are respectively connected to the positive electrode (E terminal) of the diode of the first optocoupler V1 and the positive electrode (D terminal) of the diode of the second optocoupler V2 of the detection circuit, since there is a pull-down resistor R6 with a typical value of 5KΩ inside the RXD terminal to the GND terminal, the diodes of the first optocoupler V1 and the second optocoupler V2 cannot emit light normally, and the collector and emitter of the photosensitive triodes of the first optocoupler V1 and the second optocoupler V2 are cut off and not conducting, and the state signal one outputs a high level;

[0079] From the above three detection results, it can be seen that the two wires that can make the state signal one output a low level are the TXD signal wire and the GND wire, and the other one is the RXD signal wire.

[0080] The detection process 1 can only identify the RXD signal wire, but cannot identify which one is the TXD signal wire and which one is the GND wire. In order to further identify, the detection process 2 is carried out.

[0081] As in the above solution, the second detection circuit 2 includes:

[0082] The first test circuit (F terminal), on which a resistor R5 is provided, one end of the resistor R5 is connected to the ground wire, and the other end of the resistor R5 is connected to the signal input terminal of the processor module, and the state signal two is output;

[0083] The second test circuit (G terminal), on which a resistor R4 is provided, and the resistor R4 is connected to the VCC terminal.

[0084] Working principle:

[0085] The detection process 2 is as follows:

[0086] The processor module controls the switch matrix to switch the identified RXD signal wire from the peer device to the second test circuit (G terminal) of the second detection circuit 2, and the undetermined TXD signal wire or GND wire to the first test circuit (F terminal) of the second detection circuit 2, and two tests are carried out respectively.

[0087] At this time, in the state signal two received by the processor module, when the voltage range is 1 / 3×Vcc~1 / 2×Vcc, it is confirmed that the measured wire is the GND wire. Specifically:

[0088] (1) When the GND wire is switched to the detection terminal test circuit one (F terminal), Vcc is divided by the resistor R4, the internal resistor R6 of the receiver terminal and the resistor R5, and the voltage of the resistor R5 to the local GND should be 1 / 3×Vcc~1 / 2×Vcc;

[0089] (2) When the TXD signal line is switched to the detection terminal test circuit 1 (terminal F), since the GND of the opposite end is floating, the voltage at the TXD terminal of the opposite-end transmitter cannot be applied across the resistor R5, and the voltage of the resistor R5 with respect to the local GND should be about 0V;

[0090] The internal AD converter of the processor module samples the voltage of the status signal 2. When the voltage range is 1 / 3×Vcc to 1 / 2×Vcc, it is confirmed that the GND of the opposite end is measured, and then it is identified which is the TXD signal line and which is the GND line;

[0091] At the same time, according to the characteristics of the receiver RXD terminal (the RXD terminal is usually used in conjunction with the TXD terminal to achieve bidirectional data transmission), this process further confirms the RXD signal line.

[0092] As in the above solution, the identification test method of the RS232 serial communication interface intelligent identification and switching circuit includes the following steps:

[0093] Step 1:

[0094] The output terminals of any two of the three unknown signal lines of the opposite-end device are switched to the first detection circuit, and the anode of the diode of the first optocoupler V1 and the anode of the diode of the second optocoupler V2

[0095] Three tests are carried out, respectively testing a certain combination between AB, AC, and BC, which can make the diode of the first optocoupler V1 emit light normally and the collector and emitter of the triode conduct saturated, or the diode of the second optocoupler V2 emit light normally and the collector and emitter of the triode conduct saturated;

[0096] At this time, for the status signal 1 received by the processor module, the two lines that can make the status signal 1 output a low level are the TXD signal line and the GND line, and the other one is the RXD signal line.

[0097] Step 2:

[0098] Among the three unknown signal lines of the opposite-end device, the RXD signal line measured in step 1 is connected to the test circuit 2 (terminal G) of the second detection circuit, and then the two unknown signal lines of the opposite-end device are respectively connected to the test circuit 1 (terminal F) for two tests;

[0099] At this time, for the status signal 2 received by the processor module, when the voltage range is 1 / 3×Vcc to 1 / 2×Vcc, it is confirmed that the measured line is the GND line;

[0100] Step 3:

[0101] The first detection circuit determines that the port signal is the RXD signal line, and the second detection circuit determines that the port signals are the GND signal line and the TXD signal line respectively. At this time, the processor sends a control signal to the switch matrix, and the switch matrix connects the three signal lines with the measured results to the corresponding transmitter TXD terminal, receiver RXD terminal, and ground GND terminal respectively, effectively establishing RS232 serial interface communication;

[0102] So far, the three serial port signal lines from the peer device have been completely identified. According to the identification results, the processor module controls the switch matrix to connect the three serial port signal lines to the corresponding transmitter TXD terminal, receiver RXD terminal, and ground GND terminal respectively;

[0103] The present invention provides an intelligent identification and switching circuit for RS232 serial communication interfaces, which has the characteristics of intelligently switching signal lines to the correct connection method, protecting the device from damage, saving manual cable connection modification, and effectively establishing RS232 serial interface communication.

[0104] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated and described examples here.

Claims

1. An RS232 serial communication interface intelligent identification and switching circuit, characterized in that: include: A switch matrix, wherein an input end thereof is used to connect to a peer device, and an output end of the switch matrix is ​​connected to a first detection circuit and a second detection circuit; A first detection circuit, whose input end is connected to the switch matrix, and whose output end is connected to the processor module. When the current signal passes through the first detection circuit and sends a state signal 1 to the processor, when the processor module detects that the state signal 1 is at a low level, the processor determines that the port signal is the RXD signal line, and completes the first detection; A second detection circuit, whose input end is connected to the switch matrix, and whose output end is connected to the processor module. When the current signal passes through the second detection circuit and sends the second state signal to the processor, the processor module detects that the second state signal is: a current signal with a voltage range of 1 / 3×Vcc to 1 / 2×Vcc, and the processor determines that the port signal is a GND signal line, completing the second detection; The first detection circuit determines that the port signal is the RXD signal line, and the second detection circuit determines that the port signals are the GND signal line and the TXD signal line respectively. At this time, the processor sends a control signal to the switch matrix, and the switch matrix connects the three signal lines with the measured results to the transmitter TXD end, the receiver RXD end and the ground GND end corresponding to the RS232 interface, respectively, to effectively establish RS232 serial interface communication.

2. The RS232 serial communication interface intelligent identification and switching circuit according to claim 1, characterized in that: The first detection circuit comprises: A first optical coupler V1, the anode of its diode is connected to the output end of the switch matrix, and a resistor R1 is provided on the connection line, the transistor emitter of the first optical coupler V1 is connected to the ground wire, the transistor collector of the first optical coupler V1 is connected to the VCC end, and a resistor R3 is provided on the connection line, the transistor collector of the first optical coupler V1 is connected to the signal input end of the processor module, and outputs a state signal 1; The second optocoupler V2, the positive electrode of its diode is connected to the output end of the switch matrix, and a resistor R2 is arranged on the connecting line, the emitter of the transistor of the second optocoupler V2 is connected to the ground wire, the collector of the transistor of the second optocoupler V2 is connected to the signal input end of the processor module, and outputs status signal one.

3. The RS232 serial communication interface intelligent identification and switching circuit according to claim 1, characterized in that: The second detection circuit comprises: A test circuit 1 is provided with a resistor R5, one end of the resistor R5 is connected to the ground wire, and the other end of the resistor R5 is connected to the signal input end of the processor module, and outputs a status signal 2; The test circuit 2 is provided with a resistor R4, and the resistor R4 is connected to the VCC terminal.

4. A method for intelligently identifying and testing RS232 serial communication interfaces and switching circuits, characterized in that: The following steps are involved: Step 1: Switch any two of the three unknown signal lines of the opposite device to the first detection circuit, the anode of the diode of the first optocoupler V1 and the anode of the diode of the second optocoupler V2. Three tests are conducted to test a certain combination between AB, AC and BC respectively, which can make the diode of the first optocoupler V1 emit light normally and the collector and emitter of the transistor saturated and conductive, or the diode of the second optocoupler V2 emit light normally and the collector and emitter of the transistor saturated and conductive; At this time, the status signal one received by the processor module can make the two lines of the status signal one output low level, which is the TXD signal line or the GND line, and the other is the RXD signal line. Step 2: Connect the RXD signal line measured in step 1 among the three unknown signal lines of the opposite device to the test circuit 2 of the second detection circuit, and then connect the two unknown signal lines of the opposite device to the test circuit 1 respectively, and perform two tests; At this time, in the status signal 2 received by the processor module, when the voltage range is 1 / 3×Vcc~1 / 2×Vcc, it is confirmed that the measured line is the GND line; Step 3: The first detection circuit determines that the port signal is the RXD signal line, and the second detection circuit determines that the port signals are the GND signal line and the TXD signal line respectively. At this time, the processor sends a control signal to the switch matrix, and the switch matrix connects the three signal lines with the corresponding transmitter TXD end, receiver RXD end and ground GND end respectively, effectively establishing RS232 serial interface communication.

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