A circuit for realizing RS485 communication by using double IO ports

Abstract

The utility model discloses a kind of circuit for realizing RS485 communication using double IO port, including double IO port sending circuit, RS-485 communication chip U1, pull-up and pulldown circuit, protection circuit, RS485 output interface, power supply VCC, the double IO port sending circuit is connected pull-up and pulldown circuit by RS-485 communication chip U1, the pull-up and pulldown circuit is connected RS485 output interface by protection circuit, the double IO port sending circuit, RS-485 communication chip U1, pull-up and pulldown circuit are all connected power supply VCC, the utility model reduces from original 3 IO to 2 IO, and can realize the effective transceiving of communication data, can well solve the situation of MCU IO port resource deficiency encountered in 485 communication, and the circuit scheme device is simple, low in cost, with good economy, applicability and practicality.

Description

Technical Field

[0001] This utility model relates to RS485 communication circuits, and more particularly to a circuit that uses dual I / O ports to implement RS485 communication. Background Technology

[0002] RS-485, a widely used differential serial communication standard in the industrial field, effectively suppresses common electromagnetic interference (EMI) and common-mode noise in industrial environments due to its unique differential signal transmission mechanism. Even in environments with strong interference such as inverters and motors, it maintains stable data transmission. It supports transmission distances up to 1200 meters at a baud rate of 9600bps, and a single bus can theoretically support 32 nodes, expandable to more nodes via repeaters. Combined with low-cost twisted-pair transmission media and general-purpose transceiver chips such as MAX485 and SN75176, it has become a core communication solution in scenarios such as PLC-sensor / actuator interconnection in industrial automation, communication between intersection controllers and vehicle detectors in intelligent transportation, and data acquisition from substation instruments in power monitoring. However, in actual hardware design, common RS-485 communication circuits typically require three I / O ports of a microcontroller (MCU) to achieve complete half-duplex data transmission and reception functions. Figure 1 As shown, two pins, TX and RX, are used for standard UART serial communication, responsible for data output and input. The other pin is dedicated to controlling the RS-485 transceiver's receive enable (RE) and transmit enable (DE) pins. Typically, RE and DE are shorted to simplify control, still requiring one I / O port to switch between transmit and receive modes. This approach is not problematic in high-end devices with abundant MCU resources. However, in industrial control applications using 8-bit MCUs such as the STC89C52 or resource-constrained embedded systems like IoT terminal modules, the limited number of I / O ports (usually only 4-8) and the need to drive other peripherals like button inputs, LED indicators, relay control, and ADC sampling significantly exacerbates the I / O resource shortage. This can even prevent some functions from being implemented due to insufficient I / O ports, affecting the overall flexibility and feasibility of the system design. Utility Model Content

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a circuit that uses dual I / O ports to implement RS485 communication.

[0004] To achieve the above objectives, this utility model is implemented through the following technical solution:

[0005] A circuit employing dual I / O ports for RS485 communication includes a dual I / O port transmitting circuit, an RS-485 communication chip U1, pull-up / pull-down circuits, a protection circuit, an RS485 output interface, and a power supply VCC. The dual I / O port transmitting circuit is connected to the pull-up / pull-down circuits via the RS-485 communication chip U1. The pull-up / pull-down circuits are connected to the RS485 output interface via the protection circuit. The dual I / O port transmitting circuit, the RS-485 communication chip U1, and the pull-up / pull-down circuits are all connected to the power supply VCC. The dual I / O port transmitting circuit includes resistors R1, R2, R3, R8, and R9, and a MOSFET Q1. One end of resistor R2 is connected to the power supply VCC. The other end is connected to the drain (D) of MOSFET Q1. The source (S) of MOSFET Q1 is connected to ground (GND). The gate (G) of MOSFET Q1 is connected to ground (GND) through resistor R9. The gate of MOSFET Q1 is connected to one end of resistor R8. The other end of resistor R8 is connected to the DI terminal of RS-485 communication chip U1 through resistor R3. The other end of resistor R8 is the first signal input terminal MCU_TX1. The / RE and DE terminals of RS-485 communication chip U1 are both connected to the drain (D) of MOSFET Q1. The RO terminal of RS-485 communication chip U1 is connected to one end of resistor R1. The other end of resistor R1 is the second signal input terminal MCU_RX1.

[0006] Preferably, MOSFET Q1 is an N-channel MOSFET.

[0007] Preferably, the power supply VCC is 3.3V.

[0008] Preferably, the pull-up / pull-down circuit includes resistors R4 and R5. One end of resistor R4 is connected to ground signal GND, and the other end of resistor R4 is connected to terminal B of RS-485 communication chip U1. One end of resistor R5 is connected to power supply VCC, and the other end of resistor R5 is connected to terminal A of RS-485 communication chip U1.

[0009] Preferably, the protection circuit includes resistors R6 and R7, positive temperature coefficient resistor protectors PT1 and PT2, TVS diodes D1, D2, and D3. Terminal A of the RS-485 communication chip U1 is connected to one end of resistor R7, and the other end of resistor R7 is connected to ground (GND) through TVS diode D1. Terminal B of the RS-485 communication chip U1 is connected to one end of resistor R6, and the other end of resistor R6 is connected to the positive temperature coefficient resistor protector PT1. The other end of resistor R7 is connected to the positive temperature coefficient resistor protector PT2, and the other end of resistor R6 is connected to the other end of resistor R7 through TVS diode D2. One end of TVS diode D3 is connected to the other end of resistor R6, and the other end of TVS diode D3 is connected to ground (GND).

[0010] Preferably, resistors R4 and R5 have the same resistance value.

[0011] Preferably, resistors R6 and R7 have the same resistance value.

[0012] Preferably, both the first signal input terminal MCU_TX1 and the second signal input terminal MCU_RX1 are used to connect to the MCU.

[0013] The beneficial effects of this utility model are as follows: This utility model reduces the number of I / O ports from the original 3 to 2, and can realize the effective transmission and reception of communication data. It can effectively solve the problem of insufficient MCU I / O port resources encountered in 485 communication. The circuit scheme has simple components, low cost, and good economy, applicability and practicality. Attached Figure Description

[0014] Figure 1 The circuit schematic diagram is for the background technology;

[0015] Figure 2 This is the circuit schematic diagram of this utility model. Detailed Implementation

[0016] The technical solution of this utility model will be further described below with reference to the accompanying drawings:

[0017] like Figure 2As shown, a circuit for RS485 communication using dual I / O ports includes a dual I / O port transmitting circuit 6, an RS-485 communication chip U1, pull-up / pull-down circuits 7, a protection circuit 8, an RS485 output interface 9, and a power supply VCC. The dual I / O port transmitting circuit is connected to the pull-up / pull-down circuits 7 via the RS-485 communication chip U1. The pull-up / pull-down circuits 7 are connected to the RS485 output interface 9 via the protection circuit 8. The dual I / O port transmitting circuit 6, the RS-485 communication chip U1, and the pull-up / pull-down circuits 7 are all connected to the power supply VCC. The dual I / O port transmitting circuit 6 includes resistors R1, R2, R3, R8, and R9, and a MOSFET Q1. One end of resistor R2 is connected to the power supply VCC. The source is VCC. The other end of the resistor R2 is connected to the drain (D) of the MOSFET Q1. The source (S) of the MOSFET Q1 is connected to ground (GND). The gate (G) of the MOSFET Q1 is connected to ground (GND) through the resistor R9. The gate of the MOSFET Q1 is connected to one end of the resistor R8. The other end of the resistor R8 is connected to the DI terminal of the RS-485 communication chip U1 through the resistor R3. The other end of the resistor R8 is the first signal input terminal MCU_TX1. The / RE and DE terminals of the RS-485 communication chip U1 are both connected to the drain (D) of the MOSFET Q1. The RO terminal of the RS-485 communication chip U1 is connected to one end of the resistor R1. The other end of the resistor R1 is the second signal input terminal MCU_RX1.

[0018] like Figure 2 As shown, MOSFET Q1 is an N-channel MOSFET. The power supply VCC is 3.3V.

[0019] like Figure 2 As shown, the pull-up / pull-down circuit 7 includes resistors R4 and R5. One end of resistor R4 is connected to ground signal GND, and the other end of resistor R4 is connected to terminal B of RS-485 communication chip U1. One end of resistor R5 is connected to power supply VCC, and the other end of resistor R5 is connected to terminal A of RS-485 communication chip U1.

[0020] like Figure 2As shown, the protection circuit 8 includes resistors R6 and R7, positive temperature coefficient resistor protectors PT1 and PT2, TVS diodes D1, D2, and D3. Terminal A of the RS-485 communication chip U1 is connected to one end of resistor R7, and the other end of resistor R7 is connected to ground (GND) via TVS diode D1. Terminal B of the RS-485 communication chip U1 is connected to one end of resistor R6, and the other end of resistor R6 is connected to the positive temperature coefficient resistor protector PT1. The other end of resistor R7 is connected to the positive temperature coefficient resistor protector PT2, and the other end of resistor R6 is connected to the other end of resistor R7 via TVS diode D2. One end of TVS diode D3 is connected to the other end of resistor R6, and the other end of TVS diode D3 is connected to ground (GND).

[0021] like Figure 2 As shown, resistors R4 and R5 have the same resistance value. Resistors R6 and R7 have the same resistance value. The first signal input terminal MCU_TX1 and the second signal input terminal MCU_RX1 are both used to connect to the MCU.

[0022] like Figure 2 As shown, Q1 is a low-power N-MOS transistor, controlling the transmit and receive enable of the RS-485 signal; R1, R2, and R8 are current-limiting resistors, R9 is the gate-level pull-down resistor of Q1; R4 is the B signal pull-down resistor, and R5 is the A signal pull-up resistor; C1 is the filter capacitor for the power supply VSS of chip U1; U1 is a general-purpose RS-485 communication chip; when the MCU needs to send data, Q1, R4, and R5 enable one MCU pin of MCU_TX1, simultaneously realizing data transmission and chip enable functions.

[0023] In the dual I / O port transmitting circuit 6, interface MCU_RX1 connects to the data receiving port of the system's main control MCU, MCU_TX1 connects to the data transmitting port of the system's main control MCU, and 485_3.3V connects to the system's 3.3V operating power supply; RS-485 communication chip U1 converts the TX / RX general serial port data of the main control MCU (corresponding to RO / DI of U1) into differential signal RS-485 data (corresponding to B / A of U1); interfaces 485_B and 485_A of RS485 output interface 9 are connected to output or output 485 A / B signals;

[0024] The operation of this RS-485 circuit is as follows:

[0025] When the local system MCU needs to receive external 485 data, first set MCU_TX1 high to 3.3V, turn on MOSFET Q1, and pull the / RE and DE pins of U1 low to 0V. Chip U1 is in data receiving mode, and MCU_RX1 can directly read data from the RO pin of U1.

[0026] When the local system MCU needs to send 485 data, MCU_RX1 is not working, and MCU_TX1 simultaneously performs the functions of transmit enable and data transmission. Specifically: when the MCU needs to transmit a high level "1", MCU_TX1 is first set high, Q1 is turned on, and the / RE and DE pins of U1 are 0, putting U1 in receive mode. At this time, the B line of U1 chip is pulled down to 0V by R4, and the A line is pulled up to 3.3V by R5. The voltage difference VAB on the A and B lines = V485B - V485A = 0 - 3.3 = -3.3V < -200mV, representing logic 1. Figure 2 In the middle, RS485 output interface 9 outputs logic "1"; when a low level "0" needs to be transmitted, MCU_TX1 is set low, Q1 is cut off, and the / RE and DE pins of U1 are pulled up to 3.3V by R2. U1 is in transmit mode. At this time, the "0" sent by MCU_TX1 enters the DI pin of chip U1. After being processed by U1, logic "0" is output on A / B, and logic "0" is output on RS485 output interface 9.

[0027] This module has a simple circuit function and low cost. It can effectively solve the problem of insufficient MCU IO port resources in RS-485 communication. Practical verification has shown that this circuit can work normally and successfully complete RS-485 communication, which has good practicality.

[0028] When transmitting data "1", this invention enables U1 to operate in data receiving mode by turning on Q1. Although the data "1" to be transmitted cannot enter the DI pin of U1, the A / B output logic "1" is achieved through the pull-up / pull-down resistors on the A / B lines.

[0029] The number and resistance value of R1~R8 in the circuit can be adjusted according to the actual situation; Q1 N-MOSFET can be adjusted to NPN transistor.

[0030] It should be noted that the above examples are only one specific embodiment of this utility model. Obviously, this utility model is not limited to the above embodiments and can have many variations. In short, all variations that can be directly derived or conceived by those skilled in the art from the content disclosed in this utility model should be considered within the protection scope of this utility model.

Claims

1. A circuit that uses dual I / O ports to implement RS485 communication, characterized in that, The circuit includes a dual I / O port transmitting circuit (6), an RS-485 communication chip U1, pull-up / pull-down circuits (7), a protection circuit (8), an RS485 output interface (9), and a power supply VCC. The dual I / O port transmitting circuit is connected to the pull-up / pull-down circuit (7) through the RS-485 communication chip U1. The pull-up / pull-down circuit (7) is connected to the RS485 output interface (9) through the protection circuit (8). The dual I / O port transmitting circuit (6), the RS-485 communication chip U1, and the pull-up / pull-down circuit (7) are all connected to the power supply VCC. The dual I / O port transmitting circuit (6) includes resistors R1, R2, R3, R8, R9, and a MOSFET Q.

1. One end of resistor R2 is connected to power supply VCC, and the other end of resistor R2 is connected to the drain (D) of MOSFET Q1. The source (S) of MOSFET Q1 is connected to ground signal GND. The gate (G) of MOSFET Q1 is connected to ground signal GND through resistor R9. The gate of MOSFET Q1 is connected to one end of resistor R8. The other end of resistor R8 is connected to the DI terminal of RS-485 communication chip U1 through resistor R3. The other end of resistor R8 is the first signal input terminal MCU_TX1. The / RE and DE terminals of RS-485 communication chip U1 are both connected to the drain (D) of MOSFET Q1. The RO terminal of RS-485 communication chip U1 is connected to one end of resistor R1. The other end of resistor R1 is the second signal input terminal MCU_RX1.

2. The circuit for implementing RS485 communication using dual I / O ports according to claim 1, characterized in that, The MOSFET Q1 is an N-channel MOSFET.

3. The circuit for implementing RS485 communication using dual I / O ports according to claim 1, characterized in that, The power supply VCC is 3.3V.

4. The circuit for implementing RS485 communication using dual I / O ports according to claim 1, characterized in that, The pull-up / pull-down circuit (7) includes resistors R4 and R5. One end of resistor R4 is connected to ground signal GND, and the other end of resistor R4 is connected to the B terminal of RS-485 communication chip U1. One end of resistor R5 is connected to power supply VCC, and the other end of resistor R5 is connected to the A terminal of RS-485 communication chip U1.

5. The circuit for implementing RS485 communication using dual I / O ports according to claim 1, characterized in that, The protection circuit (8) includes resistors R6 and R7, positive temperature coefficient resistor protector PT1 and PT2, TVS diodes D1, D2, and D3. Terminal A of the RS-485 communication chip U1 is connected to one end of resistor R7, and the other end of resistor R7 is connected to ground signal GND through TVS diode D1. Terminal B of the RS-485 communication chip U1 is connected to one end of resistor R6, and the other end of resistor R6 is connected to positive temperature coefficient resistor protector PT1. The other end of resistor R7 is connected to positive temperature coefficient resistor protector PT2, and the other end of resistor R6 is connected to the other end of resistor R7 through TVS diode D2. One end of TVS diode D3 is connected to the other end of resistor R6, and the other end of TVS diode D3 is connected to ground signal GND.

6. The circuit for implementing RS485 communication using dual I / O ports according to claim 4, characterized in that, The resistors R4 and R5 have the same resistance value.

7. The circuit for implementing RS485 communication using dual I / O ports according to claim 5, characterized in that, The resistance values ​​of resistor R6 and resistor R7 are the same.

8. The circuit for implementing RS485 communication using dual I / O ports according to claim 1, characterized in that, The first signal input terminal MCU_TX1 and the second signal input terminal MCU_RX1 are both used to connect to the MCU.

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