A low-cost circuit capable of self-adapting RS485 and RS422 communication

Abstract

The utility model provides a low cost and can self -adaptation RS485 and RS422 communication's circuit, the circuit includes MCU, isolation circuit, RS485RS422 conversion circuit, protection circuit and external communication interface, the UART signal and control signal of MCU are connected with RS485RS422 conversion circuit through isolation circuit respectively, RS485RS422 conversion circuit is connected with external communication port through protection circuit back, the utility model discloses can realize RS485 or RS422 external communication equipment under the automatic adjustment communication type, the utility model has the characteristics of simple realization, low in cost and high reliability.

Description

Technical Field

[0001] This utility model relates to the field of energy meters with RS422 and RS485 communication functions, and is particularly suitable for situations where energy meters have compatible communication requirements with RS422 and RS485. Background Technology

[0002] RS485 and RS422 communication offer excellent anti-interference capabilities, long-distance transmission, and multi-node capability, making them the preferred serial interfaces widely used in energy meters. RS485 communication is a two-wire half-duplex communication, while RS422 communication is a four-wire full-duplex communication. Because RS485 communication saves signal lines and has more connection points, it is more widely used in the current market. However, for some energy meters with high drive capability and high transmission speed, RS422 communication is required and its application is relatively less common. Due to the different wiring methods of RS485 and RS422 communication, and the different communication tools used by field personnel, some markets have requested that meters with RS422 communication functionality also be compatible with RS485 communication to facilitate field personnel.

[0003] To solve this problem, some solutions on the market use a combination of an RS485 chip and an RS232 chip, which is not only costly but also has a complex circuit, failing to meet market demands. Utility Model Content

[0004] The purpose of this invention is to address the issue of energy meters with RS422 communication functionality needing to be compatible with RS485 communication functionality. It proposes a circuit using an RS485 chip to achieve adaptive RS485 and RS422 communication. This allows the energy meter to communicate using either RS422 or RS485 communication tools. This design not only simplifies the circuit structure and improves communication efficiency but also has strong versatility and adaptability, making it widely applicable in various industrial control and data transmission scenarios.

[0005] The technical solution of this utility model is:

[0006] This invention provides a low-cost circuit that can adapt to RS485 and RS422 communication. It includes an MCU, an isolation circuit, an RS485 / RS422 conversion circuit, a protection circuit, and an external communication interface. The UART signal and control signal of the MCU are respectively connected to the RS485 / RS422 conversion circuit through the isolation circuit. The RS485 / RS422 conversion circuit is connected to the external communication interface through the protection circuit.

[0007] Furthermore, the isolation circuit includes resistors R1-R6, optocouplers U1, U2, U3, and diodes D1 and D2;

[0008] The UART transmission signal of the MCU is denoted as MCU_TXD_485. The MCU transmission signal MCU_TXD_485 is connected to the cathode of the diode side of the optocoupler U3. The anode of the diode side of the optocoupler U3 is connected to the power supply VCC3V3 of the MCU through resistor R3. The collector of the transistor side of the optocoupler U3 is connected to the DI pin of the RS485 chip U5 of the RS485 / RS422 conversion circuit and one end of resistor R6. The other end of resistor R6 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit. The emitter of the transistor side of the optocoupler U3 is connected to the ground MGND of the RS485 / RS422 conversion circuit.

[0009] The UART receive signal of the MCU is denoted as MCU_RXD_485. The MCU receive signal MCU_RXD_485 is connected to the collector of the transistor side of the optocoupler U1 and one end of the resistor R1. The other end of the resistor R1 is connected to the power supply VCC3V3 of the MCU. The emitter of the transistor side of the optocoupler U1 is connected to the ground DGND of the MCU. The anode of the diode side of the optocoupler U1 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit through the resistor R4. The cathode of the diode side of the optocoupler U1 is connected to the anode of the diodes D1 and D2. The cathodes of the diodes D1 and D2 are respectively connected to the RO pin of the RS485 chips U4 and U5 of the RS485 / RS422 conversion circuit.

[0010] The MCU control signal is denoted as MCU_CTL_485. The MCU control signal MCU_CTL_485 is connected to the cathode of the diode side of the optocoupler U2 through resistor R2. The anode of the optocoupler U2 is connected to the power supply VCC3V3 of the MCU. The collector of the transistor side of the optocoupler U2 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit. The emitter of the transistor side of the optocoupler U2 is connected to the RE and DE pins of the RS485 chip U5 of the RS485 / RS422 conversion circuit and one end of resistor R5. The other end of resistor R5 is connected to ground MGND.

[0011] Furthermore, the RS485 / RS422 conversion circuit includes resistors R7-R11 and RS485 chips U4 and U5. The VCC pin of RS485 chips U4 and U5 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit, and the connection points of the two chips to the power supply are connected to ground MGND through capacitors C1 and C2, respectively. The GND pin of RS485 chips U4 and U5 is connected to ground MGND. The A pin of RS485 chips U4 and U5 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit through resistors R8 and R10, respectively. The B pin of RS485 chips U4 and U5 is connected to ground MGND through resistors R9 and R11, respectively. The RE and DE pins of RS485 chip U4 are grounded to ground MGND through resistor R7, and the DI pin of RS485 chip U4 is grounded to ground MGND.

[0012] Furthermore, the protection circuit includes TVS diodes D3-D8 and thermistors RM1 and RM2;

[0013] The A pin of the RS485 chip U4 is connected to one end of the TVS diode D3 and the thermistor RM1. The A pin of the RS485 chip 5 is connected to one end of the TVS diode D6 and the thermistor RM2. The other ends of the TVS diodes D3 and D6 are connected to ground MGND. The other ends of the thermistors RM1 and RM2 are respectively connected to pins 1 and 2 of the external communication interface J1.

[0014] Pin B of the RS485 chip U4 is connected to pin 2 of the TVS diode D5 and the external communication interface J1. Pin B of the RS485 chip U5 is connected to pin 4 of the TVS diode D8 and the external communication interface J1. The other ends of the TVS diodes D5 and D8 are connected to the power supply MDC5V of the RS485 / RS422 conversion circuit.

[0015] The TVS diode D4 is connected between pins A and B of the RS485 chip U4, and the TVS diode D5 is connected between pins A and B of the RS485 chip U5.

[0016] The beneficial effects of this utility model are:

[0017] This utility model discloses an adaptive RS485 and RS422 communication circuit. Through a combination of a microcontroller unit, isolation circuit, conversion circuit, protection circuit, and external communication interface, it achieves signal isolation, automatic communication mode identification, and flexible switching of operating states. It features simple implementation, low cost, and high reliability.

[0018] This invention employs optocouplers for signal isolation, uses two RS485 chips to process transmit and receive signals, and adjusts the operating mode via control signals. It adaptively supports RS485 or RS422 communication based on the wiring method of the external communication interface, enabling half-duplex or full-duplex communication. Furthermore, this invention includes protection circuitry to provide overvoltage and overcurrent protection, enhancing the system's reliability and stability.

[0019] This invention relates to energy meters with RS422 communication function. Depending on the external wiring method, communication can be achieved using either RS485 or RS422 communication tools. The energy meter automatically adjusts to either RS485 or RS422 communication mode, which is beneficial for the standardization of communication tools used by on-site personnel and improves work efficiency.

[0020] Other features and advantages of this invention will be described in detail in the following detailed description section. Attached Figure Description

[0021] The above and other objects, features and advantages of the present invention will become more apparent from the accompanying drawings, in which like reference numerals generally represent like parts.

[0022] Figure 1 The circuit block diagram of this invention, which is low-cost and adaptable to RS485 and RS422 communication, is shown.

[0023] Figure 2 The circuit diagram of this invention is shown, which is low-cost and adaptable to RS485 and RS422 communication. Detailed Implementation

[0024] Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. Although preferred embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0025] Figure 1 The circuit block diagram of this invention, which is low-cost and adaptable to RS485 and RS422 communication, is shown.

[0026] like Figure 1As shown, this utility model provides a low-cost circuit that can adapt to RS485 and RS422 communication. It includes an MCU, an isolation circuit, an RS485 / RS422 conversion circuit, a protection circuit, and an external communication interface. The UART signal and control signal of the MCU are respectively connected to the RS485 / RS422 conversion circuit through isolation lines. The RS485 / RS422 conversion circuit is connected to the external communication interface through the protection circuit.

[0027] In one example, such as Figure 2 The isolation circuit shown mainly consists of resistors R1-R6, optocouplers U1, U2, and U3; diodes D1 and D2; the UART transmission signal of the MCU is denoted as MCU_TXD_485; the MCU transmission signal MCU_TXD_485 is connected to the cathode of the diode side of optocoupler U3; the anode of the diode side of optocoupler U3 is connected to the MCU power supply VCC3V3 through resistor R15; the collector of the transistor side of optocoupler U3 is connected to the DI pin of chip U5 and one end of resistor R6; the other end of resistor R6 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit; and the emitter of the transistor side of optocoupler U3 is connected to the ground MGND of the RS485 / RS422 conversion circuit.

[0028] The UART receive signal of the MCU is denoted as MCU_RXD_485. The MCU receive signal MCU_RXD_485 is connected to the collector of the transistor side of the optocoupler U1 and one end of the resistor R1. The other end of the resistor R1 is connected to the MCU power supply VCC3V3. The emitter of the transistor side of the optocoupler U1 is connected to the ground DGND of the MCU. The anode of the diode side of the optocoupler U1 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit through the resistor R4. The cathode of the diode side of the optocoupler U1 is connected to the anode of the diodes D1 and D2. The cathodes of the diodes D1 and D2 are respectively connected to the RO pins of the chips U4 and U5.

[0029] The MCU control signal is denoted as MCU_CTL_485. The MCU control signal MCU_CTL_485 is connected to the cathode of the diode side of the optocoupler U2 through resistor R2. The anode of the optocoupler U2 is connected to the MCU power supply VCC3V3. The collector of the transistor side of the optocoupler U2 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit. The emitter of the transistor side of the optocoupler U2 is connected to the / RE and DE pins of chip U5 and one end of resistor R5. The other end of resistor R5 is connected to ground MGND.

[0030] In one example, such as Figure 2The RS485 / RS422 conversion circuit is shown, mainly consisting of resistors R7-R11, chips U4 and U5. The VCC pins of chips U4 and U5 are connected to the RS485 / RS422 conversion circuit power supply MDC5V, and the connection point is connected to ground MGND through capacitors C1 and C2 respectively. The GND pins of chips U4 and U5 are connected to ground MGND. The A pins of chips U4 and U5 are connected to the RS485 / RS422 conversion circuit power supply MDC5V through resistors R8 and R10 respectively. The B pins of chips U4 and U5 are connected to ground MGND through resistors R9 and R11 respectively. The / RE and DE pins of chip U4 are grounded to ground MGND through resistor R7, and the DI pin of chip U4 is also grounded to ground MGND.

[0031] In one example, such as Figure 2 The protection circuit shown mainly consists of TVS diodes D3-D8, thermistors RM1 and RM2. Pins A of chips U4 and U5 are connected to TVS diodes D3 and D6 and thermistors RM1 and RM2, respectively. The other ends of TVS diodes D3 and D6 are connected to ground MGND. The other ends of thermistors RM1 and RM2 are connected to pins 1 and 2 of external interface J1, respectively. Pins B of chips U4 and U5 are connected to TVS diodes D5 and D8 and pins 2 and 4 of external interface J1, respectively. The other ends of TVS diodes D5 and D8 are connected to the power supply MDC5V of the RS485 / RS422 conversion circuit. Pins A and B of chips U4 and U5 are connected across TVS diodes D4 and D5, respectively.

[0032] In practice:

[0033] This utility model provides a low-cost RS485 and RS422 communication circuit that adapts to the wiring method of the external communication interface.

[0034] like Figure 2As shown, when the external communication interface is wired as RS485, pins 1 and 2 of terminal J1 are not connected to signals, and pins 3 and 4 are connected to the T+ / A and T- / B signals of the communication device, respectively. Since there is no received signal at pins 1 and 2 of terminal J1, the / RE and DE pins of chip U4 are pulled low by resistor R7, and chip U4 is in receive mode. When the RO pin of chip U4 outputs a high voltage, and the MCU control signal MCU_CTL_485 outputs a high level, optocoupler U2 is turned off. The / RE and DE pins of chip U5 are pulled low by resistor R5, and chip U5 is in receive mode. Pins 3 and 4 of terminal J1 are connected... The received signal passes through thermistor RM2 and TVS diodes D6, D7, and D8 for protection before reaching pins A and B of chip U5. Chip U5 combines the signals from pins A and B with the / RE signal and outputs them through pin RO. The high and low level changes of pin RO will cause the diode side of optocoupler U1 to be cut off or turned on through resistor R1 and diode D2. When optocoupler U1 is cut off, the UART receive signal MCU_RXD_485 of the MCU is pulled up to a high level by resistor R1. When optocoupler U1 is turned on, MCU_RXD_485 is at a low level, completing the transmission of external signals to the MCU.

[0035] After the MCU completes the data reception, it sends the data via the UART transmission signal MCU_TXD_485. The MCU needs to output a low level from the control signal MCU_CTL_485, which turns on the optocoupler U2. The / RE and DE pins of chip U5 are output high level by resistor R5, and chip U5 is in transmit mode. When MCU_TXD_485 is high, optocoupler U3 is off. The DI pin of chip U5 is pulled high by resistor R6. When MCU_TXD_485 is low, optocoupler U3 turns on, and the DI pin of chip U5 becomes low due to the conduction of optocoupler U3. After the signal conversion of the DE and DI pins, chip U5 outputs through pins A and B. The signals from pins A and B of chip U5 are protected by thermistor RM2 and TVS diodes D6, D7, and D8 before reaching pins 3 and 4 of external terminal J1, completing the transmission of MCU signals to external signals.

[0036] In this mode, the MCU's UART reception and transmission are controlled by the control signal MCU_CTL_485 and cannot be performed simultaneously; it is a half-duplex mode.

[0037] like Figure 2As shown, when the external communication interface is connected via RS422, pins 1-4 of terminal J1 are connected to the R+, R-, T+ / A, and T- / B pins of the communication device, respectively. The / RE and DE pins of chip U4 are pulled low by resistor R7, indicating chip U4 is in receive mode. The received signals from pins 1 and 2 of terminal J1 are protected by thermistor RM1 and TVS diodes D3, D4, and D5 before reaching pins A and B of chip U4. Chip U4 combines the signals from pins A and B with the / RE signal and outputs them through pin RO. When the MCU control signal MCU_CTL_485 outputs a high level, the optocoupler U... 2. When the chip U5 is off, the / RE and DE pins are pulled down to low level by resistor R5, and the chip U5 is in receive mode. There is no receive signal at pins 3 and 4 of the J1 terminal block. The RO pin of the chip U5 outputs a high level. The high and low level changes of the RO pin will cause the diode side of the optocoupler U1 to be cut off or turned on through resistor R1 and diode D1. When the optocoupler U1 is off, the UART receive signal MCU_RXD_485 of the MCU is pulled up to a high level by resistor R1. When the optocoupler U1 is on, MCU_RXD_485 is at a low level, completing the transmission of external signals to the MCU.

[0038] While the MCU receives data, if there is data to send, the MCU can output a low level from the control signal MCU_CTL_485. When MCU_CTL_485 outputs a low level, optocoupler U2 is turned on, and the / RE and DE pins of chip U5 are output high level by resistor R5, indicating that chip U5 is in transmit mode. When the MCU's UART transmit signal MCU_TXD_485 is high, optocoupler U3 is turned off, and the DI pin of chip U5 is pulled high by resistor R6. When MCU_TXD_485 is low, optocoupler U3 is turned on, and the DI pin of chip U5 becomes low due to the conduction of optocoupler U3. After the signal conversion of chip U5 combined with the DE and DI pins, the signal is output through pins A and B. The signals from pins A and B of chip U5 are protected by thermistor RM2 and TVS diodes D6, D7, and D8 before reaching the transmit terminals 3 and 4 of external terminal J1, completing the transmission of the MCU signal to the external signal.

[0039] In this mode, the MCU's UART reception is not controlled by the MCU_CTL_485 control signal.

[0040] The MCU's UART transmission is controlled by the control signal MCU_CTL_485. Reception and transmission can be performed simultaneously, which is a full-duplex mode.

[0041] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A low cost and adaptive RS485 and RS422 communication circuit, characterized in that It includes an MCU, an isolation circuit, an RS485 / RS422 conversion circuit, a protection circuit, and an external communication interface. The UART signal and control signal of the MCU are respectively connected to the RS485 / RS422 conversion circuit through the isolation circuit. The RS485 / RS422 conversion circuit is connected to the external communication interface through the protection circuit.

2. The low cost and adaptive RS485 and RS422 communication circuit as claimed in claim 1, wherein, The isolation circuit includes resistors R1-R6, optocouplers U1, U2, U3, and diodes D1 and D2; The UART transmission signal of the MCU is denoted as MCU_TXD_485. The MCU transmission signal MCU_TXD_485 is connected to the cathode of the diode side of the optocoupler U3. The anode of the diode side of the optocoupler U3 is connected to the power supply VCC3V3 of the MCU through resistor R3. The collector of the transistor side of the optocoupler U3 is connected to the DI pin of the RS485 chip U5 of the RS485 / RS422 conversion circuit and one end of resistor R6. The other end of resistor R6 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit. The emitter of the transistor side of the optocoupler U3 is connected to the ground MGND of the RS485 / RS422 conversion circuit. The UART receive signal of the MCU is denoted as MCU_RXD_485. The MCU receive signal MCU_RXD_485 is connected to the collector of the transistor side of the optocoupler U1 and one end of the resistor R1. The other end of the resistor R1 is connected to the power supply VCC3V3 of the MCU. The emitter of the transistor side of the optocoupler U1 is connected to the ground DGND of the MCU. The anode of the diode side of the optocoupler U1 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit through the resistor R4. The cathode of the diode side of the optocoupler U1 is connected to the anode of the diodes D1 and D2. The cathodes of the diodes D1 and D2 are respectively connected to the RO pin of the RS485 chips U4 and U5 of the RS485 / RS422 conversion circuit. The MCU control signal is denoted as MCU_CTL_485. The MCU control signal MCU_CTL_485 is connected to the cathode of the diode side of the optocoupler U2 through resistor R2. The anode of the optocoupler U2 is connected to the power supply VCC3V3 of the MCU. The collector of the transistor side of the optocoupler U2 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit. The emitter of the transistor side of the optocoupler U2 is connected to the RE and DE pins of the RS485 chip U5 of the RS485 / RS422 conversion circuit and one end of resistor R5. The other end of resistor R5 is connected to ground MGND.

3. The low-cost circuit capable of adapting to both RS485 and RS422 communication as described in claim 1, characterized in that, The RS485 / RS422 conversion circuit includes resistors R7-R11 and RS485 chips U4 and U5. The VCC pin of RS485 chips U4 and U5 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit, and the connection points of the two chips to the power supply are connected to ground MGND through capacitors C1 and C2, respectively. The GND pin of RS485 chips U4 and U5 is connected to ground MGND. The A pin of RS485 chips U4 and U5 is connected to the power supply MDC5V of the RS485 / RS422 conversion circuit through resistors R8 and R10, respectively. The B pin of RS485 chips U4 and U5 is connected to ground MGND through resistors R9 and R11, respectively. The RE and DE pins of RS485 chip U4 are grounded to ground MGND through resistor R7, and the DI pin of RS485 chip U4 is grounded to ground MGND.

4. The low-cost circuit capable of adapting to both RS485 and RS422 communication as described in claim 3, characterized in that, The protection circuit includes TVS diodes D3-D8 and thermistors RM1 and RM2; The A pin of the RS485 chip U4 is connected to one end of the TVS diode D3 and the thermistor RM1. The A pin of the RS485 chip 5 is connected to one end of the TVS diode D6 and the thermistor RM2. The other ends of the TVS diodes D3 and D6 are connected to ground MGND. The other ends of the thermistors RM1 and RM2 are respectively connected to pins 1 and 2 of the external communication interface J1. Pin B of the RS485 chip U4 is connected to pin 2 of the TVS diode D5 and the external communication interface J1. Pin B of the RS485 chip U5 is connected to pin 4 of the TVS diode D8 and the external communication interface J1. The other ends of the TVS diodes D5 and D8 are connected to the power supply MDC5V of the RS485 / RS422 conversion circuit. The TVS diode D4 is connected between pins A and B of the RS485 chip U4, and the TVS diode D5 is connected between pins A and B of the RS485 chip U5.

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