RS232 serial port multiplexing circuit

Abstract

This utility model relates to a multiplexing circuit for an RS232 serial port, including a first MOSFET, a second MOSFET, and a third MOSFET. The gate of the first MOSFET is connected to a software-controlled GIPO signal, its source is grounded, and its drain is connected to the gate of the third MOSFET in one path and to the standby power supply via a second resistor in another. The gate of the second MOSFET is connected to a software-controlled GIPO signal, its source is connected to pin 1 of a DB9 connector, and its drain is the RS232 carrier detection signal input. The gate of the third MOSFET is connected to the first MOSFET in one path and to ground in another. Its source is connected to the external power supply output, and its drain is connected to pin 1 of the DB9 connector. The first MOSFET is an NMOS transistor, while the second and third MOSFETs are PMOS transistors. This utility model allows the first pin of the DB9 connector to be used as an RS232 carrier detection signal input or as a power supply interface for external power output via software control, facilitating user adjustments to the RS232 serial port functionality at any time.

Description

Technical Field

[0001] This utility model relates to the field of electronic computers, and in particular to a multiplexing circuit for an RS232 serial port. Background Technology

[0002] RS232 (Recommended Standard 232) is a serial physical interface standard developed by the Electronic Industries Association (EIA) in the United States. It is widely used for data transmission between computers and external devices (such as modems, printers, and sensors). Currently, RS-232 serial ports are the most widely used serial interface in the computer and communications industries and are the most commonly used interface in industrial control equipment.

[0003] RS232 serial ports typically use two types of connectors: the DB9 connector with 9 pins and the DB25 connector with 25 pins. The DB9 connector is most commonly used in industrial control equipment. The pinouts of the 9 pins of the commonly used DB9 connector in industrial control equipment are shown in Table 1.

[0004] Table 1. Pin Description of DB9 Connector

[0005] Pin number Pin name Function Description 1 DCD Data carrier detection 2 RXD Receive data 3 TXD Send data 4 DTR Data terminal ready 5 GND Grounding wire (common grounding) 6 DSR Data equipment ready 7 RTS Request sent 8 CTS Allow sending (clear sending) 9 RI Ringing indicator

[0006] In this context, pin 1 of the DB9 connector is typically used as the RS232 carrier detection (DCD) signal input. Simultaneously, industrial control equipment sometimes reuses pin 1 of the DB9 connector as a power supply interface to reduce external power supply and wiring. In existing technology, industrial control equipment usually manually selects whether to use the DB9 connector gate as the RS232 carrier detection signal input or the power supply interface through physical switching methods such as jumpers or switches. This requires disassembling the device to adjust the physical interface, making it inconvenient to adjust the multiplexing function. Utility Model Content

[0007] The purpose of this invention is to provide a multiplexing circuit for an RS232 serial port. By controlling the first pin of the DB9 connector through software, it can be used as an RS232 carrier detection signal input or as a power supply interface. This allows the multiplexing function to be controlled through a driver or setting interface, making it convenient for users to adjust the function of the RS232 serial port at any time.

[0008] To achieve the above objectives, this utility model provides a multiplexing circuit for an RS232 serial port, including a first MOSFET, a second MOSFET, and a third MOSFET. The gate of the first MOSFET is connected to a software-controlled GIPO signal, its source is grounded, and its drain is connected to the gate of the third MOSFET in one path and to the standby power supply via a second resistor in another path. The gate of the second MOSFET is connected to a software-controlled GIPO signal, its source is connected to pin 1 of a DB9 connector, and its drain is the RS232 carrier detection signal input. The gate of the third MOSFET is connected to the first MOSFET in one path and to ground in another path, its source is connected to the external power supply output, and its drain is connected to pin 1 of a DB9 connector. The first MOSFET is an NMOS transistor, and the second and third MOSFETs are PMOS transistors.

[0009] When the GIPO signal is low, the first MOSFET is off, the second MOSFET is on, and the third MOSFET is off, and pin 1 of the DB9 connector is switched to RS232 carrier detection signal input; when the GIPO signal is high, the first MOSFET is on, the second MOSFET is off, and the third MOSFET is on, and pin 1 of the DB9 connector is switched to power supply interface for external power output.

[0010] The GIPO signal is grounded after passing through the first capacitor.

[0011] The capacitance of the first capacitor is 0.1μF and the rated voltage is 16V.

[0012] The GIPO signal is passed through a first resistor to obtain an intermediate signal. One of the intermediate signals is grounded after passing through a first capacitor, another is connected to the gate of a first MOS transistor, and the third is connected to the gate of a second MOS transistor.

[0013] The second resistor has a resistance of 10kΩ, the standby power supply is a 5V power supply, and the external power supply output is a 5V power supply.

[0014] The gate of the third MOS transistor is grounded via the second capacitor.

[0015] The second capacitor has a capacitance of 0.1μF and a rated voltage of 16V.

[0016] A fuse is connected in series between the source of the third MOSFET and the power supply output to the external power source.

[0017] A diode is connected in series between the source of the third MOS transistor and the power supply output to the external power source.

[0018] The first MOSFET is model LBSS139WT1G.

[0019] The second and third MOSFETs are model HM1W3401AL.

[0020] The diode D4 is model SM340AF.

[0021] In summary, the RS232 serial port multiplexing circuit of this invention uses software to control pin 1 of the DB9 connector as an RS232 carrier detection signal input or as a power supply interface for external power output. This allows for control of the multiplexing function via a driver or settings interface, enabling users to easily adjust the RS232 serial port functionality at any time. The multiplexing operation of this RS232 serial port multiplexing circuit is simple, saving disassembly time, avoiding the risk of material waste from disassembly, and reducing the risk of electrostatic damage introduced during disassembly. The circuit control logic is simple and compatible with various industrial control platforms. The circuit is safe and reliable, preventing interference between power and signals, and will not affect the normal operation of the device motherboard or damage external RS232 devices even if the user sets incorrectly. Attached Figure Description

[0022] The technical solution and other beneficial effects of this utility model will become apparent from the following detailed description of specific embodiments, in conjunction with the accompanying drawings.

[0023] Figure 1 This is a circuit diagram of a preferred embodiment of the RS232 serial port multiplexing circuit of this utility model.

[0024] Figure 2 for Figure 1 The circuit diagram of the DB9 connector portion of the embodiment. Detailed Implementation

[0025] To further illustrate the technical means and effects of this utility model, the following detailed description is provided in conjunction with the preferred embodiments of this utility model and their accompanying drawings.

[0026] See Figure 1-2The RS232 serial port multiplexing circuit of this utility model includes a first MOSFET Q1, a second MOSFET Q2, and a third MOSFET Q3. The gate of the first MOSFET Q1 is connected to the software-controlled GIPO signal COM1_PWREN, the source is grounded, and the drain is connected to the gate of the third MOSFET Q3 in one path and to the standby power supply P5VSB through the second resistor R2 in another path. The gate of the second MOSFET Q2 is connected to the software-controlled GIPO signal COM1_PWREN, the source is connected to pin 1 of the DB9 connector, and the drain is the RS232 carrier detection signal input. The gate of the third MOSFET Q3 is connected to the first MOSFET Q1 in one path and grounded in another path. The source is connected to the external power supply P5V, and the drain is connected to pin 1 of the DB9 connector. The first MOSFET Q1 is an NMOS transistor, and the second MOSFET Q2 and the third MOSFET Q3 are PMOS transistors.

[0027] When the GIPO signal COM1_PWREN is low, the first MOSFET Q1 is off, the second MOSFET Q2 is on, and the third MOSFET Q3 is off, and pin 1 of the DB9 connector is switched to RS232 carrier detection signal input; when the GIPO signal COM1_PWREN is high, the first MOSFET Q1 is on, the second MOSFET Q2 is off, and the third MOSFET Q3 is on, and pin 1 of the DB9 connector is switched to power supply interface output.

[0028] This invention provides an RS232 serial port multiplexing circuit. By controlling pin 1 of the DB9 connector via software, it can be used as an RS232 carrier detection signal input or as a power supply interface for external power output. This allows for multiplexing control via a driver or settings interface, enabling users to easily adjust the RS232 serial port functionality. The multiplexing operation of this RS232 serial port multiplexing circuit is simple, saving disassembly time, avoiding the risk of material waste from disassembly, and reducing the risk of electrostatic damage introduced during disassembly. The circuit control logic is simple and compatible with various industrial control platforms. The circuit is safe and reliable, preventing interference between power and signals. Even if the user sets incorrectly, it will not affect the normal operation of the device motherboard or damage external RS232 devices.

[0029] Specifically, when a device using the RS232 serial port multiplexing circuit of this invention is connected to a full-function RS232 device, that is, when pin 1 of the DB9 connector needs to be used as an RS232 serial port, if the user incorrectly configures the settings so that pin 1 of the DB9 connector is switched to 5V power supply output, in this case, because the second MOSFET Q2 is cut off and the negative terminal of the body diode points to the source of the second MOSFET Q2, the RS232 carrier detection signal input detection is in a high-impedance state. The default device is present, carrier detection is ineffective, and RS232 transmission and other flow control functions are normal. Therefore, the solution of this invention can still ensure normal operation even in the event of user error.

[0030] Specifically, when a device using the RS232 serial port multiplexing circuit of this utility model is connected to a power-required device, that is, when the first pin of the DB9 connector needs to be used as a power supply interface for external power output, if the user incorrectly sets the first pin of the DB9 connector to the RS232 carrier detection signal input function, at this time, since the second MOSFET Q2 is turned on and the third MOSFET Q3 is turned off, the first pin of the DB9 connector remains at a low level. The device internally believes that no external device is connected, and at the same time, the external device does not receive power and remains turned off, which does not affect the normal operation of other devices. Therefore, the solution of this utility model can still ensure the normal operation of other functions except for the RS232 interface even in the case of user error, and will not damage the device motherboard and RS232 device.

[0031] Preferably, the GIPO signal COM1_PWREN is grounded after passing through the first capacitor C1.

[0032] Furthermore, the GIPO signal COM1_PWREN is passed through the first resistor R1 to obtain the intermediate signal COM1_PWREN_R. The intermediate signal COM1_PWREN_R is grounded through the first capacitor C1, connected to the gate of the first MOS transistor Q1, and connected to the gate of the second MOS transistor Q2.

[0033] Specifically, the capacitance of the first capacitor C1 is 0.1μF and the rated voltage is 16V.

[0034] Furthermore, the second resistor R2 has a resistance of 10kΩ, the standby power supply P5VSB is a 5V power supply, and the external power supply output P5V is a 5V power supply.

[0035] Preferably, the gate of the third MOS transistor Q3 is grounded via the second capacitor C741.

[0036] Specifically, the second capacitor C741 has a capacitance of 0.1μF and a rated voltage of 16V.

[0037] Preferably, a fuse F6 is connected in series between the source of the third MOSFET Q3 and the external power supply P5V. When the power demand of the external device exceeds the power supply capacity of the device, the fuse F6 cuts off the external power supply to protect the safety of the device's motherboard.

[0038] Preferably, a diode D4 is connected in series between the source of the third MOSFET Q3 and the external power supply P5V. When the motherboard is powered off and an external powered device is connected, the diode D4 can prevent the external power supply from flowing back into the motherboard of the device and causing motherboard malfunction.

[0039] Preferably, the first MOSFET Q1 is of model LBSS139WT1G, and the second MOSFET Q2 and the third MOSFET Q3 are of model HM1W3401AL.

[0040] Preferably, the diode D4 is of model SM340AF.

[0041] In summary, this utility model provides an RS232 serial port multiplexing circuit. By controlling pin 1 of the DB9 connector via software, it can be used as an RS232 carrier detection signal input or as a power supply interface for external power output. This allows for multiplexing control via a driver or settings interface, enabling users to easily adjust the RS232 serial port functionality at any time. The multiplexing operation of this RS232 serial port multiplexing circuit is simple, saving disassembly time, avoiding the risk of material waste from disassembly, and reducing the risk of electrostatic damage introduced during disassembly. The circuit control logic is simple and compatible with various industrial control platforms. The circuit is safe and reliable, preventing interference between power and signals. Even if the user sets incorrectly, it will not affect the normal operation of the device motherboard or damage external RS232 devices.

[0042] As described above, those skilled in the art can make various other corresponding changes and modifications based on the technical solution and concept of this utility model, and all such changes and modifications should fall within the protection scope of the appended claims of this utility model.

Claims

1. A multiplexing circuit for RS232 serial ports, characterized in that, The system includes a first MOSFET (Q1), a second MOSFET (Q2), and a third MOSFET (Q3). The gate of the first MOSFET (Q1) is connected to the software-controlled GIPO signal (COM1_PWREN), its source is grounded, and its drain is connected to the gate of the third MOSFET (Q3) in one path and to the standby power supply (P5VSB) through a second resistor (R2). The gate of the second MOSFET (Q2) is connected to the software-controlled GIPO signal (COM1_PWREN), its source is connected to pin 1 of the DB9 connector, and its drain is the RS232 carrier detection signal input. The gate of the third MOSFET (Q3) is connected to the first MOSFET (Q1) in one path and to ground in another path. Its source is connected to the external power supply output (P5V), and its drain is connected to pin 1 of the DB9 connector. The first MOSFET (Q1) is an NMOS transistor, while the second MOSFET (Q2) and the third MOSFET (Q3) are PMOS transistors.

2. The multiplexing circuit for RS232 serial ports of claim 1, wherein, The GIPO signal (COM1_PWREN) is grounded after passing through the first capacitor (C1); the gate of the third MOS transistor (Q3) is grounded after passing through the second capacitor (C741).

3. The multiplexing circuit for RS232 serial ports of claim 2, wherein, The capacitance of the first capacitor (C1) and the second capacitor (C741) is 0.1μF, and the rated voltage is 16V.

4. The multiplexing circuit for RS232 serial ports of claim 2, wherein, The GIPO signal (COM1_PWREN) is passed through the first resistor (R1) to obtain the intermediate signal (COM1_PWREN_R). The intermediate signal (COM1_PWREN_R) is connected to ground through the first capacitor (C1), connected to the gate of the first MOS transistor (Q1), and connected to the gate of the second MOS transistor (Q2).

5. The multiplexing circuit for RS232 serial ports of claim 1, wherein, The second resistor (R2) has a resistance of 10kΩ, the standby power supply (P5VSB) is a 5V power supply, and the external power supply output (P5V) is a 5V power supply.

6. The multiplexing circuit for RS232 serial ports of claim 1, wherein, The first MOSFET (Q1) is model LBSS139WT1G.

7. The multiplexing circuit for RS232 serial ports of claim 1, wherein, The second MOSFET (Q2) and the third MOSFET (Q3) are model HM1W3401AL.

8. The multiplexing circuit for RS232 serial ports of claim 1, wherein, A fuse (F6) is connected in series between the source of the third MOSFET (Q3) and the power supply (P5V) output to the external power source.

9. The RS232 serial port multiplexing circuit as described in claim 1, characterized in that, A diode (D4) is connected in series between the source of the third MOSFET (Q3) and the power supply (P5V) output to the external power source.

10. The RS232 serial port multiplexing circuit as described in claim 9, characterized in that, The diode (D4) is model number SM340AF.

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