Low-cost current anti-backflow circuit of Debug serial port of embedded system

Abstract

The utility model discloses a low-cost current anti-backflow circuit of a Debug serial port of an embedded system, which is characterized in that a pin DGBTX and a pin DGBRX of a Debug serial port module J11 are respectively connected with a 74LVC1G125GW three-state buffer to form a power-off automatic cut-off circuit to prevent the current of the Debug serial port module from flowing back to a circuit board of the embedded system. The device is small in size, flexible in layout and low in cost and supports high-speed serial ports; the device supports a wide rate range, and is suitable for all rates of the serial port.

Description

Technical Field

[0001] The utility model relates to the technical field of protection circuits for embedded systems, in particular to a low-cost current backflow prevention circuit for a Debug serial port of an embedded system. Background Art

[0002] In embedded systems, the debug serial port module is usually directly connected to the MCU / MPU to print debug information. Although this solution is convenient and easy, and there will be no problems during normal use, when the MCU / MPU loses power and the debug serial port module is still connected to the computer, the current of the debug serial port module will flow back to the MCU / MPU through the TX and RX signal lines, which will cause product malfunctions, such as the LED dimly lit. If the current flows back for a long time, it will damage the MCU / MPU.

[0003] The existing solution is to connect an isolation chip π121U31 in series between the Debug serial port module and the MCU / MPU. This solution is not only costly but also has a low rate. The rate of the isolation chip π121U31 is only 150Kbps, and the usage scenarios are limited. If a higher rate is required, a more expensive π121M31 is required, so it is necessary to improve it. Utility Model Content

[0004] In view of the deficiencies in the prior art, the purpose of the utility model is to provide a low-cost current backflow prevention circuit for the Debug serial port of an embedded system, which has a simple circuit structure, a small device size, a flexible layout, a low cost and supports high-speed serial ports.

[0005] In order to achieve the above purpose, the technical solution adopted by the utility model is: a low-cost current backflow prevention circuit for the debug serial port of an embedded system, the circuit board of the embedded system is provided with a signal pin UART0_TX_M0_DEBUG, a signal pin UART0_RX_M0_DEBUG and a power pin VCC_3V3_S3, the debug serial port module J11 is provided with a pin DGB_TX, a pin DGB_RX and a pin GND, and the pin GND is grounded

[0006] Pin DGB_TX is electrically connected to the Y pin of the first tri-state buffer U25 of model 74LVC1G125GW, and pin A of the tri-state buffer U25 is electrically connected to the signal pin UART0_TX_M0_DEBUG;

[0007] Pin DGB_RX is electrically connected to the A pin of the second tri-state buffer U26 of model 74LVC1G125GW, and pin Y of the tri-state buffer U26 is electrically connected to the signal pin UART0_RX_M0_DEBUG;

[0008] The pin VCC of the tri-state buffer U25 and the pin VCC of the tri-state buffer U26 are electrically connected to the power pin VCC_3V3_S3 respectively;

[0009] After the embedded system circuit board is powered off, the power supply of the power pin VCC_3V3_S3 of the embedded system circuit board becomes 0V, and the pin Y of the three-state buffer U25 and the pin A of the three-state buffer U26 are both in a high-impedance state, which is used to cut off the current of the Debug serial port module.

[0010] A resistor R217 is connected in series between the pin DGB_TX and the Y pin of the tri-state buffer U25, and a bidirectional voltage regulator diode D22 is connected in series between the pin DGB_TX and the ground terminal;

[0011] A resistor R218 is connected in series between the pin DGB_RX and the A pin of the tri-state buffer U26, and a bidirectional voltage regulator diode D23 is connected in series between the pin DGB_RX and the ground terminal;

[0012] A capacitor C388 is connected in series between the pin VCC of the tri-state buffer U25 and the ground terminal, and a capacitor C389 is connected in series between the pin VCC of the tri-state buffer U26 and the ground terminal.

[0013] The pin OE and the pin GND of the tri-state buffer U25 are grounded respectively; the pin OE and the pin GND of the tri-state buffer U26 are grounded respectively.

[0014] After adopting the above structure, the advantages of the utility model compared with the prior art are: the utility model has a simple circuit structure, a small device size, a flexible layout, a low cost and supports high-speed serial ports; the utility model supports a wide range of rates and is suitable for all serial port rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural schematic diagram of the utility model.

[0016] Figure 2 It is a circuit schematic diagram of the utility model. DETAILED DESCRIPTION

[0017] A low-cost current backflow prevention circuit for the debug serial port of an embedded system. Figure 1 and 2As shown, the circuit board of the embedded system is provided with a signal pin UART0_TX_M0_DEBUG, a signal pin UART0_RX_M0_DEBUG and a power pin VCC_3V3_S3, and the debug serial port module J11 is provided with a pin DGB_TX, a pin DGB_RX and a pin GND, the pin GND is grounded, the pin DGB_TX is electrically connected to the Y pin of the first tri-state buffer U25 of model 74LVC1G125GW, the pin A of the tri-state buffer U25 is electrically connected to the signal pin UART0_TX_M0_DEBUG, the pin OE and the pin GND of the tri-state buffer U25 are grounded respectively; the pin DGB_RX is electrically connected to the second tri-state buffer U25 of model 74LVC1G125GW The A pin of the three-state buffer U26, the Y pin of the three-state buffer U26 is electrically connected to the signal pin UART0_RX_M0_DEBUG, and the OE pin and the GND pin of the three-state buffer U26 are grounded respectively; a resistor R217 is connected in series between the pin DGB_TX and the Y pin of the three-state buffer U25, and a bidirectional voltage regulator diode D22 is connected in series between the pin DGB_TX and the ground terminal; a resistor R218 is connected in series between the pin DGB_RX and the A pin of the three-state buffer U26, and a bidirectional voltage regulator diode D23 is connected in series between the pin DGB_RX and the ground terminal; a capacitor C388 is connected in series between the pin VCC of the three-state buffer U25 and the ground terminal, and a capacitor C389 is connected in series between the pin VCC of the three-state buffer U26 and the ground terminal.

[0018] The pin VCC of the tri-state buffer U25 and the pin VCC of the tri-state buffer U26 are electrically connected to the power pin VCC_3V3_S3 respectively; the debug serial port module J11 is connected to the computer via a USB cable, and the circuit board of the embedded system supplies power to the tri-state buffer U25 and the tri-state buffer U26 via the power pin VCC_3V3_S3, and the pin Y of the tri-state buffer U25 and the pin A of the tri-state buffer U26 are both in the on state. After the circuit board of the embedded system is powered off, the power supply of the power pin VCC_3V3_S3 of the circuit board of the embedded system becomes 0V, and the pin Y of the tri-state buffer U25 and the pin A of the tri-state buffer U26 are both in the high impedance state, which is used to cut off the current of the debug serial port module.

[0019] The utility model connects two three-state buffers 74LVC1G125GW in series between the debug serial port module and the MCU / MPU of the embedded system, respectively, to solve the current backflow problem of the debug serial port module. The cost of the technical solution of the utility model is less than half of the technical solution using π121U31, and the maximum rate of the technical solution of the utility model supports 200Mbps, which basically meets the requirements of all serial port rates and enhances the stability and reliability of the system. The technical problems of cost, small supported rate range and small applicable scope of the technical solution using π121U31 in the prior art are solved.

[0020] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, according to the concept of the present invention, there will be changes in the specific implementation methods and application scopes. The contents of this specification should not be understood as limiting the present invention.

Claims

1. A low-cost current backflow prevention circuit for the debug serial port of an embedded system, wherein a circuit board of the embedded system is provided with a signal pin UART0_TX _M0_DEBUG, a signal pin UART0_RX _M0_DEBUG and a power pin VCC_3V3_S3, and wherein: The debug serial port module J11 is provided with pins DGB_TX, DGB_RX and GND. Pin GND is grounded. Pin DGB_TX is electrically connected to the Y pin of the first tri-state buffer U25 of model 74LVC1G125GW, and pin A of the tri-state buffer U25 is electrically connected to the signal pin UART0_TX _M0_DEBUG; Pin DGB_RX is electrically connected to pin A of a second tri-state buffer U26 of model 74LVC1G125GW, and pin Y of the tri-state buffer U26 is electrically connected to signal pin UART0_RX _M0_DEBUG; The pin VCC of the tri-state buffer U25 and the pin VCC of the tri-state buffer U26 are electrically connected to the power pin VCC_3V3_S3 respectively; After the embedded system circuit board is powered off, the power supply of the power pin VCC_3V3_S3 of the embedded system circuit board becomes 0V, and the pin Y of the three-state buffer U25 and the pin A of the three-state buffer U26 are both in a high-impedance state, which is used to cut off the current of the Debug serial port module.

2. The low-cost current backflow prevention circuit of the debug serial port of an embedded system according to claim 1, characterized in that: A resistor R217 is connected in series between the pin DGB_TX and the Y pin of the tri-state buffer U25, and a bidirectional voltage regulator diode D22 is connected in series between the pin DGB_TX and the ground terminal; A resistor R218 is connected in series between the pin DGB_RX and the A pin of the tri-state buffer U26, and a bidirectional voltage regulator diode D23 is connected in series between the pin DGB_RX and the ground terminal.

3. The low-cost current backflow prevention circuit of the debug serial port of an embedded system according to claim 1, characterized in that: A capacitor C388 is connected in series between the pin VCC of the tri-state buffer U25 and the ground terminal, and a capacitor C389 is connected in series between the pin VCC of the tri-state buffer U26 and the ground terminal.

4. A low-cost current backflow prevention circuit for a debug serial port of an embedded system according to any one of claims 1 to 3, characterized in that: The pin OE and the pin GND of the tri-state buffer U25 are grounded respectively; the pin OE and the pin GND of the tri-state buffer U26 are grounded respectively.

Images