Communication circuit between indoor and outdoor units of air conditioner, multi-split air conditioner and its communication control method

Abstract

This invention discloses a communication circuit for indoor and outdoor units of an air conditioner, a multi-split air conditioner, and a communication control method thereof. The communication circuit includes: an outdoor unit receiving circuit; multiple outdoor unit transmitting circuits, which are connected in parallel and then in series with the outdoor unit receiving circuit to the same communication bus; each outdoor unit transmitting circuit is used to connect to one indoor unit; and a transmitting selection circuit, whose input is connected to the outdoor unit controller, and whose multiple outputs are respectively connected to the control terminals of each outdoor unit transmitting circuit. The transmitting selection circuit selects one of the outdoor unit transmitting circuits according to the control signal of the outdoor unit controller, so that the corresponding indoor unit establishes a communication connection with the outdoor unit controller through the communication bus. This invention reduces the number of outdoor unit receiving circuits from N to 1 by reusing the outdoor unit receiving circuit, significantly simplifying the outdoor unit communication circuit structure of multi-split air conditioners, reducing controller space occupation, and lowering hardware costs.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, and in particular to a communication circuit for indoor and outdoor units of an air conditioner, a multi-split air conditioner, and a communication control method thereof. Background Technology

[0002] Multi-split air conditioning systems typically consist of one outdoor unit and multiple indoor units. To achieve centralized control and operational status monitoring, real-time and reliable data communication is required between the outdoor unit and each indoor unit. In existing technologies, current loop communication is a commonly used communication method between the indoor and outdoor units. It utilizes changes in current signals within the loop to transmit information and typically employs optocouplers (or optocouplers) to achieve electrical isolation and level conversion of the communication signals, thereby improving the communication's anti-interference capability and system security.

[0003] In the current design of the current loop communication circuit for multi-split air conditioners, the outdoor unit controller is configured with a complete communication interface circuit for each indoor unit it is connected to. Each communication interface circuit includes a transmitting optocoupler and its peripheral driving circuit responsible for sending data, and a receiving optocoupler and its peripheral signal processing circuit responsible for receiving data.

[0004] For example, in a multi-split air conditioning system containing one outdoor unit and five indoor units, the outdoor unit controller needs to have five independent transmitting circuits and five independent receiving circuits, requiring a total of ten optocouplers and dozens of matching electronic components such as resistors, capacitors, and transistors. As the capacity of the multi-split system increases, the number of connected indoor units N increases, and the number of communication optocouplers and peripheral components required in the outdoor unit controller will increase linearly at a ratio of 2N.

[0005] This "one-to-one" circuit architecture leads to the following significant drawbacks: Firstly, the use of numerous electronic components occupies a large amount of valuable layout space on the outdoor unit controller's printed circuit board (PCB), increasing the controller's size and design complexity. Secondly, the large number of optocouplers and their peripheral circuits directly results in a significant increase in hardware material costs, which is detrimental to improving the market competitiveness of air conditioning products. Furthermore, the increased number of components theoretically also has a potential negative impact on the overall reliability of the system. Summary of the Invention

[0006] The embodiments of the present invention provide a communication circuit for indoor and outdoor units of an air conditioner, a multi-split air conditioner and its communication control method, aiming to solve the technical problem that the communication circuit of the outdoor unit of the existing multi-split air conditioner system has serious redundancy design, resulting in a large occupation of controller space resources and high hardware costs.

[0007] In a first aspect, the present invention provides a communication circuit for indoor and outdoor units of an air conditioner, comprising: an outdoor unit receiving circuit; multiple outdoor unit transmitting circuits, wherein the multiple outdoor unit transmitting circuits are connected in parallel to each other and then connected in series with the outdoor unit receiving circuit to the same communication bus, and each outdoor unit transmitting circuit is used to connect to an indoor unit; and a transmitting selection circuit, wherein its input terminal is connected to an outdoor unit controller, and its multiple output terminals are respectively connected to the control terminals of each of the outdoor unit transmitting circuits; wherein the transmitting selection circuit is configured to select one of the outdoor unit transmitting circuits according to the control signal of the outdoor unit controller, so that the indoor unit corresponding to the selected outdoor unit transmitting circuit establishes a communication connection with the outdoor unit controller through the communication bus.

[0008] Furthermore, each of the outdoor unit transmitting circuits includes a first transistor driving unit and a first optocoupler switching unit. The first transistor driving unit is connected to the transmitting gating circuit, and the first optocoupler switching unit is connected to the first transistor driving unit and the communication bus, respectively. The first transistor driving unit drives the first optocoupler switching unit to turn on or off according to the control signal of the transmitting gating circuit, so as to change the current loop state of the communication bus.

[0009] Furthermore, the transmission gating circuit includes a multiple-to-one chip, the input terminal of which is connected to the data transmission terminal of the outdoor unit controller, the multiple output terminals of which are respectively connected to the first transistor driving unit in each of the outdoor unit transmission circuits, and the control terminal of which is connected to the gating control terminal of the outdoor unit controller.

[0010] Furthermore, the first transistor driving unit includes a first transistor, a first resistor, and a second resistor. The base of the first transistor is connected to the output terminal of the transmitting gating circuit via the first resistor, the collector of the first transistor is connected to the input terminal of the first optocoupler switching unit, and the second resistor is connected in parallel between the base and emitter of the first transistor.

[0011] Furthermore, the first optocoupler switching unit includes a first optocoupler, a third resistor, and a fourth resistor. The positive terminal of the first optocoupler's input is connected to the power supply via the third resistor. The negative terminal of the first optocoupler's input is connected to the output of the first transistor driving unit. The output of the first optocoupler is connected to the communication bus. The fourth resistor is connected in parallel to the output of the first optocoupler.

[0012] Furthermore, the outdoor unit receiving circuit includes a second transistor driving unit and a second optocoupler switching unit. The input terminal of the second optocoupler switching unit is connected to the communication bus to sense the current loop state on the communication bus. The output terminal of the second optocoupler switching unit is connected to the input terminal of the second transistor driving unit, and the output terminal of the second transistor driving unit is connected to the outdoor unit controller to output the received signal to the outdoor unit controller.

[0013] Furthermore, the second transistor driving unit includes a second transistor, a fifth resistor, a sixth resistor, and a first capacitor. The base of the second transistor is connected to the power supply and the output terminal of the second optocoupler switching unit via the fifth resistor. The emitter of the second transistor is grounded. The collector of the second transistor is connected to the outdoor unit controller and to the power supply via the sixth resistor. The first capacitor is connected in parallel between the collector and emitter of the second transistor.

[0014] Furthermore, the second optocoupler switching unit includes a second optocoupler and a seventh resistor. The positive input terminal of the second optocoupler is connected to the power supply, the negative input terminal of the second optocoupler is connected to the communication bus, the output terminal of the second optocoupler is connected to the input terminal of the second transistor driving unit, and the seventh resistor is connected in parallel between the positive and negative input terminals of the second optocoupler.

[0015] Furthermore, it also includes a communication power supply circuit, which is connected to the outdoor unit receiving circuit and the outdoor unit transmitting circuit respectively, and is used to provide operating voltage to the outdoor unit receiving circuit and the outdoor unit transmitting circuit.

[0016] Secondly, the present invention provides a multi-split air conditioner, which includes an outdoor unit, multiple indoor units, and an air conditioner indoor-outdoor unit communication circuit as described in the first aspect. The air conditioner indoor-outdoor unit communication circuit is disposed inside the outdoor unit, and the multiple indoor units are respectively connected to the outdoor unit through the air conditioner indoor-outdoor unit communication circuit.

[0017] Thirdly, the present invention provides an air conditioner communication control method, which is applied to the multi-split air conditioner described in the second aspect. The method includes: controlling the sending gating circuit to select one of the outdoor unit sending circuits; sending a data packet to the corresponding indoor unit through the selected outdoor unit sending circuit; after the data packet is sent, determining whether a return data packet from the indoor unit is received through the outdoor unit receiving circuit within a preset time; if the return data packet is received within the preset time, controlling the sending gating circuit to select the next outdoor unit sending circuit, and returning to the step of sending a data packet to the corresponding indoor unit through the selected outdoor unit sending circuit.

[0018] Compared with the prior art, the present invention simplifies the multiple receiving circuits required in the prior art (the same number as the indoor units) to only one receiving circuit by connecting multiple outdoor unit transmitting circuits in parallel and then connecting them in series with a single outdoor unit receiving circuit, and by using a transmitting gating circuit to selectively conduct each transmitting channel. This significantly reduces the number of optocouplers and peripheral components used, and effectively reduces the hardware cost of the outdoor unit controller and the space occupied by the printed circuit board layout. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 A schematic block diagram of the communication circuit between the indoor and outdoor units of an air conditioner provided in an embodiment of the present invention; Figure 2 A circuit diagram of the communication circuit between the indoor and outdoor units of an air conditioner provided in an embodiment of the present invention; Figure 3 A schematic block diagram of a multi-split air conditioner provided in an embodiment of the present invention; Figure 4 A flowchart illustrating the steps of the air conditioner communication control method provided in this embodiment of the invention; Figure 5 A flowchart of the sub-steps of the air conditioner communication control method provided in an embodiment of the present invention.

[0021] Explanation of reference numerals in the attached figures: 100. Communication circuit between indoor and outdoor air conditioning units; 200. Indoor unit; 300. Outdoor unit controller; 400. Outdoor unit; 10. Outdoor unit receiving circuit; 11. Second transistor driving unit; 12. Second optocoupler switching unit; 20. Outdoor unit transmitting circuit; 21. First transistor driving unit; 22. First optocoupler switching unit; 30. Transmitting selection circuit; 40. Communication power supply circuit. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0024] Please see Figure 1 and Figure 2 This embodiment provides a communication circuit for indoor and outdoor units of an air conditioner, comprising: an outdoor unit receiving circuit 10; multiple outdoor unit transmitting circuits 20, wherein the multiple outdoor unit transmitting circuits 20 are connected in parallel and then connected in series with the outdoor unit receiving circuit 10 to the same communication bus, and each outdoor unit transmitting circuit 20 is used to connect to an indoor unit 200; and a transmitting selection circuit 30, the input of which is connected to an outdoor unit controller 300, and multiple outputs of which are respectively connected to the control terminals of each outdoor unit transmitting circuit 20; wherein the transmitting selection circuit 30 is configured to select one of the outdoor unit transmitting circuits 20 according to the control signal of the outdoor unit controller 300, so that the indoor unit 200 corresponding to the selected outdoor unit transmitting circuit 20 establishes a communication connection with the outdoor unit controller 300 through the communication bus.

[0025] In practical implementation, the aforementioned communication circuit between the outdoor and indoor units of an air conditioner is mainly used in multi-split air conditioning systems. A multi-split air conditioning system typically consists of one outdoor unit and multiple indoor units 200 (e.g., indoor units A, B, C, D, E, etc.). The outdoor unit and each indoor unit 200 need to exchange data through a communication circuit to achieve functions such as centralized control, status monitoring, and coordination of operating parameters.

[0026] In traditional multi-split air conditioner communication circuit designs, the outdoor unit controller 300 requires an independent, complete communication interface circuit for each connected indoor unit 200. Each interface circuit includes both an independent transmitting circuit and a separate receiving circuit. For example, with one outdoor unit connecting five indoor units, the outdoor unit controller 300 needs five transmitting circuits and five receiving circuits, requiring ten optocouplers and numerous external resistors, capacitors, transistors, and other components. As the number of indoor units 200 increases, the required number of optocouplers and external components multiplies, leading to limited space on the controller's printed circuit board, a significant increase in hardware costs, and potentially adverse effects on the overall system reliability due to the excessive number of components.

[0027] In view of this, the core improvement of the air conditioner indoor and outdoor unit communication circuit in this embodiment is to connect multiple transmitting circuits corresponding to each indoor unit 200 in parallel on the outdoor unit side, and connect the parallel nodes in series with a single receiving circuit to the same communication bus. At the same time, a transmitting gating circuit 30 is introduced to selectively control the conduction of each transmitting channel, thereby realizing time-division multiplexing of a single receiving circuit.

[0028] Figure 1 A schematic block diagram of the communication circuit between the indoor and outdoor units of the air conditioner is shown. Figure 1 As shown, the communication circuit between the indoor and outdoor units of this air conditioner mainly includes an outdoor unit receiving circuit 10, multiple outdoor unit transmitting circuits 20, and a transmitting gating circuit 30. Specifically, the multiple outdoor unit transmitting circuits 20 are connected in parallel, and the common connection terminal formed by the parallel connection is connected in series with the single outdoor unit receiving circuit 10 to the same communication bus (shown as COM-RXD in the figure). The communication bus serves as a common physical channel for data transmission and reception between the outdoor unit and each indoor unit 200, carrying the loop signal required for current loop communication.

[0029] Each outdoor unit transmitting circuit 20 is connected to one indoor unit 200. For example, the first outdoor unit transmitting circuit 20 establishes a communication link with indoor unit A, the second outdoor unit transmitting circuit 20 establishes a communication link with indoor unit B, and so on. Specifically, the outdoor unit transmitting circuit 20 is connected to the communication circuit of the indoor unit 200. The communication circuit of the indoor unit 200 consists of an indoor unit transmitting circuit and an indoor unit receiving circuit. The indoor unit transmitting circuit is responsible for sending data to the outdoor unit, and the indoor unit receiving circuit is responsible for receiving data sent by the outdoor unit. The outdoor unit transmitting circuit 20 is connected to the indoor unit transmitting circuit and indoor unit receiving circuit of each indoor unit 200. The function of each outdoor unit transmitting circuit 20 is, under the control of the outdoor unit controller 300, to load the data signal to be sent to the corresponding indoor unit 200 onto the communication bus, and to realize the data transmission by changing the current loop state on the communication bus.

[0030] The transmitting gating circuit 30, as the core component for channel selection, has its input terminal electrically connected to the outdoor unit controller 300 (specifically, the main control chip within the outdoor unit controller 300) to receive control signals from the outdoor unit controller 300. The transmitting gating circuit 30 has multiple output terminals, the number of which matches the number of indoor units 200 connected to the outdoor unit. Each output terminal is connected to a corresponding control terminal of the transmitting circuit 20 of each outdoor unit.

[0031] During operation, the outdoor unit controller 300 outputs a corresponding control signal to the transmitting gating circuit 30 based on which indoor unit 200 it needs to communicate with. The transmitting gating circuit 30 is configured to select one of the multiple outdoor unit transmitting circuits 20 based on this control signal, making it operational, while the other unselected outdoor unit transmitting circuits 20 remain in a cutoff or high-impedance state, preventing interference with the communication bus. Under the control of the outdoor unit controller 300's data transmission signal, the selected outdoor unit transmitting circuit 20 sends data packets to the communication bus, which then transmits them to the corresponding indoor unit 200. When the outdoor unit completes data transmission and needs to receive return data from the indoor unit 200, since the outdoor unit transmitting circuit 20 remains connected to the communication bus, and only one outdoor unit receiving circuit 10 is provided on the communication bus, the data signal returned by the indoor unit 200 will be received by this single outdoor unit receiving circuit 10 via the communication bus and converted into a signal level recognizable by the outdoor unit controller 300.

[0032] In this way, the outdoor unit controller 300 can sequentially and cyclically select each outdoor unit transmitting circuit 20 through the transmitting gating circuit 30, thereby realizing time-division communication with each indoor unit 200. Although the outdoor unit is connected to multiple indoor units 200, only one outdoor unit receiving circuit 10 needs to be configured on the outdoor unit side to complete the task of receiving data returned by all indoor units 200, realizing hardware multiplexing of the receiving circuit.

[0033] This embodiment simplifies the multiple receiving circuits required in the prior art (the same number as the indoor unit 200) to only one receiving circuit by connecting multiple outdoor unit transmitting circuits 20 in parallel and then connecting them in series with a single outdoor unit receiving circuit 10, and by using a transmitting gating circuit 30 to selectively conduct each transmitting channel. This significantly reduces the number of optocouplers and peripheral components used, effectively reducing the hardware cost of the outdoor unit controller 300 and the space occupied by the printed circuit board layout.

[0034] In one embodiment, see Figure 2 Each of the outdoor unit transmitting circuits 20 includes a first transistor driving unit 21 and a first optocoupler switching unit 22. The first transistor driving unit 21 is connected to the transmitting gating circuit 30, and the first optocoupler switching unit 22 is connected to the first transistor driving unit 21 and the communication bus, respectively. The first transistor driving unit 21 drives the first optocoupler switching unit 22 to turn on or off according to the control signal of the transmitting gating circuit 30, so as to change the current loop state of the communication bus.

[0035] In specific implementation, each outdoor unit transmitting circuit 20 includes a first transistor driving unit 21 and a first optocoupler switching unit 22. The first transistor driving unit 21 serves as the control interface of the outdoor unit transmitting circuit 20, with its input terminal connected to the corresponding output terminal of the transmitting gating circuit 30. It receives the channel selection control signal output by the transmitting gating circuit 30 and the data transmission signal from the outdoor unit controller 300. The first optocoupler switching unit 22 serves as the execution part of the outdoor unit transmitting circuit 20. One end of its connection is to the output terminal of the first transistor driving unit 21, and the other end is connected to the communication bus COM-RXD. It controls the current loop state on the communication bus under the action of the driving signal. Specifically, the first transistor driving unit 21 is connected to the transmitting gating circuit 30, and the first optocoupler switching unit 22 is connected to both the first transistor driving unit 21 and the communication bus. During operation, when the outdoor unit controller 300 needs to communicate with a specific indoor unit 200, the outdoor unit controller 300 first outputs a valid gating control signal to the outdoor unit transmitting circuit 20 corresponding to that indoor unit 200 through the transmitting gating circuit 30. This gating control signal is applied to the input terminal of the first transistor driving unit 21, enabling the first transistor driving unit 21 to enter the working state. Subsequently, the outdoor unit controller 300 transmits the data signal to be transmitted (usually represented as a high-low level sequence) to the selected first transistor driving unit 21 through the transmitting gating circuit 30. The first transistor driving unit 21 controls the on or off state of its output terminal according to the changes in the received data signal level, thereby driving the subsequent first optocoupler switching unit 22. Specifically, when the data signal is high, the first transistor driving unit 21 drives the first optocoupler switching unit 22 to enter the on state; when the data signal is low, the first transistor driving unit 21 drives the first optocoupler switching unit 22 to enter the off state.

[0036] The switching on and off of the first optocoupler switching unit 22 directly changes its impedance state in the communication bus loop, thereby causing a corresponding change in the current magnitude in the current loop of the communication bus. Since the communication circuit on the indoor unit 200 side is also connected to this communication bus, the indoor unit 200 can deduce the data information sent by the outdoor unit by detecting the current change on the communication bus. At the same time, when the first optocoupler switching unit 22 is on, it provides a low-impedance path for the communication bus, ensuring that the communication loop has sufficient drive current when the indoor unit 200 returns data to the outdoor unit; while when it is off, a higher impedance is introduced into the communication bus loop, and the resulting current difference becomes the basis for the receiving side to identify the signal.

[0037] It should be noted that when the sending selection circuit 30 does not select a certain outdoor unit sending circuit 20, the first transistor driving unit 21 in the outdoor unit sending circuit 20 is in the off state, and the corresponding first optocoupler switching unit 22 is also kept off, which will not interfere with the communication bus. This ensures that only one outdoor unit sending circuit 20 is in the working state at the same time, ensuring the reliability and uniqueness of signal transmission on the communication bus.

[0038] In the above manner, the first transistor driving unit 21 drives the first optocoupler switching unit 22 to turn on or off according to the control signal of the sending gating circuit 30, so as to change the current loop state of the communication bus, thereby realizing the conversion of the digital signal of the outdoor unit controller 300 into the current loop signal on the communication bus and completing the data transmission function.

[0039] Further, see Figure 2 The transmitting gating circuit 30 includes a multi-to-one chip. The input terminal of the multi-to-one chip is connected to the data transmitting terminal of the outdoor unit controller 300. The multiple output terminals of the multi-to-one chip are respectively connected to the first transistor driving unit 21 in each of the outdoor unit transmitting circuits 20. The control terminal of the multi-to-one chip is connected to the gating control terminal of the outdoor unit controller 300.

[0040] In specific implementation, the transmission gating circuit 30 includes a multi-select chip U30, which has one input terminal, multiple output terminals, and at least one control terminal. Specifically, the input terminal of the multi-select chip U30 is connected to the data transmission terminal TXD of the outdoor unit controller 300, and is used to receive data signals to be transmitted from the outdoor unit controller 300 to the indoor unit 200. The multiple output terminals of the multi-select chip U30 are respectively connected to the first transistor driving unit 21 in each outdoor unit transmission circuit 20 to selectively allocate data signals to designated outdoor unit transmission channels. The control terminals of the multi-select chip U30 (COMM_A0, COMM_A1, COMM_A2 in the figure) are connected to the gating control terminal of the outdoor unit controller 300, and are used to receive channel selection control signals issued by the outdoor unit controller 300.

[0041] During operation, when the outdoor unit controller 300 needs to communicate with a specific indoor unit 200, it first outputs a corresponding address code signal to the control terminal of the multi-select chip U30 through the selection control terminal, enabling the channel inside the multi-select chip U30 corresponding to the indoor unit 200 to be activated. At this time, a low-impedance path is formed between the input terminal and the selected output terminal of the multi-select chip U30, while other unselected output terminals are in a high-impedance state, which will not interfere with the communication bus. Subsequently, the outdoor unit controller 300 sends a data packet signal to be sent through the data transmission terminal TXD. This signal enters through the input terminal of the multi-select chip U30 and is transmitted by the selected output terminal to the first transistor driver unit 21 in the corresponding outdoor unit transmission circuit 20. After receiving the data signal, the first transistor driver unit 21 drives the first optocoupler switching unit 22 to perform the corresponding on or off action, loading the data onto the communication bus, thereby completing the data transmission to the indoor unit 200.

[0042] The multi-choice chip U30 can be a commonly used analog switch chip or multiplexer chip in the art. For example, an 8-to-1 analog switch chip 74HC4051 can be used, which has three address control terminals and one enable terminal, and can select up to eight channels through three address lines. Of course, depending on the number of indoor units 200 in the actual application, other specifications of chips such as 4-to-1 or 16-to-1 can also be selected, or multiple chips can be cascaded to expand the number of channels. This invention does not impose specific limitations on this. In addition, the sending selection circuit 30 can usually set a decoupling capacitor C6 at the power supply terminal of the multi-choice chip U30, and a pull-up or pull-down resistor (such as resistor R26) at the control terminal to ensure the stable operation of the chip.

[0043] This embodiment uses an integrated multi-select chip to control the selection of the transmission channel. The circuit structure is simple and the selection action is reliable, effectively ensuring the orderly time-division communication between the outdoor unit and multiple indoor units 200.

[0044] In one embodiment, see Figure 2 The first transistor driving unit 21 includes a first transistor Q83 (or Q84), a first resistor R830 (or R840), and a second resistor R831 (or R841). The base of the first transistor Q83 (or Q84) is connected to the output terminal of the transmitting gating circuit 30 via the first resistor R830 (or R840). The collector of the first transistor Q83 (or Q84) is connected to the input terminal of the first optocoupler switching unit 22. The second resistor R831 (or R841) is connected in parallel between the base and emitter of the first transistor Q83 (or Q84).

[0045] In specific implementation, the first transistor driving unit 21 includes a first transistor Q83 (or Q84), a first resistor R830 (or R840), and a second resistor R831 (or R841). The first transistor Q83 (or Q84) is used for signal amplification and switching drive functions. The first resistor R830 (or R840) is a base-limiting current resistor, and the second resistor R831 (or R841) is a base-pull-down resistor. The specific connection relationship is as follows: the base of the first transistor Q83 (or Q84) is connected to the corresponding output terminal of the transmitting gating circuit 30 via the first resistor R830 (or R840), used to receive the data signal and gating control signal output by the transmitting gating circuit 30. The collector of the first transistor Q83 (or Q84) serves as the output terminal of this driving unit and is connected to the input terminal of the subsequent first optocoupler switching unit 22, used to control the operating state of the first optocoupler switching unit 22. The emitter of the first transistor Q83 (or Q84) is grounded. The second resistor R831 (or R841) is connected in parallel between the base and emitter of the first transistor Q83 (or Q84) to reliably pull the base potential low when there is no input signal, preventing the transistor from being mistakenly turned on due to external interference.

[0046] During operation, when the sending selection circuit 30 selects the external unit sending circuit 20 and outputs a high-level data signal, this high level is applied to the base of the first transistor Q83 (or Q84) through the first resistor R830 (or R840), causing the first transistor Q83 (or Q84) to enter a saturated conduction state. At this time, a low impedance is presented between the collector and emitter of the first transistor Q83 (or Q84), and current can flow through the collector into the input terminal of the subsequent first optocoupler switching unit 22, driving the first optocoupler switching unit 22 to conduct. Conversely, when the data signal is low, the base level of the first transistor Q83 (or Q84) is pulled low, the first transistor Q83 (or Q84) enters a cutoff state, there is no current output from the collector, and the first optocoupler switching unit 22 is turned off accordingly.

[0047] By switching the first transistor Q83 (or Q84) on and off, the switching control of the first optocoupler switching unit 22 is realized, thereby controlling the current loop state on the communication bus and completing the transmission of data signals. The setting of the second resistor R831 (or R841) ensures the determinism of the base potential when there is no driving signal, improving the anti-interference capability of the circuit.

[0048] In one embodiment, see Figure 2The first optocoupler switching unit 22 includes a first optocoupler U830 (or U840), a third resistor R832 (or R842), and a fourth resistor R833 (or R843). The positive terminal of the input of the first optocoupler U830 (or U840) is connected to the power supply via the third resistor R832 (or R842). The negative terminal of the input of the first optocoupler U830 (or U840) is connected to the output of the first transistor driving unit 21. The output of the first optocoupler U830 (or U840) is connected to the communication bus. The fourth resistor R833 (or R843) is connected in parallel to the output of the first optocoupler U830 (or U840).

[0049] In specific implementation, the first optocoupler switching unit 22 includes a first optocoupler U830 (or U840), a third resistor R832 (or R842), and a fourth resistor R833 (or R843). The first optocoupler U830 (or U840) is used to realize electrical signal isolation and switching control, the third resistor R832 (or R842) is the current limiting resistor on the input side of the optocoupler, and the fourth resistor R833 (or R843) is the bypass resistor on the output side of the optocoupler. The specific connection relationship is as follows: the positive terminal (anode) of the input terminal of the first optocoupler U830 (or U840) is connected to the power supply VCC through the third resistor R832 (or R842), and the negative terminal (cathode) of the input terminal of the first optocoupler U830 (or U840) is connected to the output terminal of the first transistor driving unit 21, i.e., the collector of the first transistor Q83. The output of the first optocoupler U830 (or U840) is connected to the communication bus COM-RXD, and is connected in series in the entire communication loop. The fourth resistor R833 (or R843) is connected in parallel to the output of the first optocoupler U830 (or U840), that is, it is connected across the two ends of the optocoupler output side.

[0050] During operation, when the first transistor driving unit 21 drives the first optocoupler U830 (or U840) to conduct, i.e., the first transistor Q83 is saturated and conducting, current flows through the input side of the optocoupler, the internal light-emitting diode lights up, and the photosensitive device on the output side of the optocoupler conducts, resulting in a low-impedance state in the communication bus loop. At this time, the fourth resistor R833 (or R843) is short-circuited by the conducting output side, and the communication loop current is relatively large. When the first optocoupler U830 (or U840) is turned off, the optocoupler output side is open-circuited, and the fourth resistor R833 (or R843) is connected in series in the communication bus loop, significantly reducing the communication loop current. During the data transmission phase, the outdoor unit changes the current in the communication loop by controlling the conduction and deactivation of the first optocoupler U830 (or U840), and the indoor unit 200 can deduce the data signal by detecting this current change. During the data reception phase, after the outdoor unit completes data transmission, it keeps the first optocoupler U830 (or U840) in the ON state. At this time, the fourth resistor R833 (or R843) is short-circuited, and the communication loop has sufficient drive current. The data signal returned by the indoor unit 200 can be accurately received by the outdoor unit receiving circuit 10 via the communication bus. The bypassing function of the fourth resistor R833 (or R843) ensures the difference in communication loop current between the transmitting and receiving states, which is one of the key design features for realizing the multiplexing of the receiving circuit.

[0051] In one embodiment, see Figure 2 The outdoor unit receiving circuit 10 includes a second transistor driving unit 11 and a second optocoupler switching unit 12. The input terminal of the second optocoupler switching unit 12 is connected to the communication bus to sense the current loop state on the communication bus. The output terminal of the second optocoupler switching unit 12 is connected to the input terminal of the second transistor driving unit 11. The output terminal of the second transistor driving unit 11 is connected to the outdoor unit controller 300 to output the received signal to the outdoor unit controller 300.

[0052] In specific implementation, the outdoor unit receiving circuit 10 includes a second transistor driving unit 11 and a second optocoupler switching unit 12. The second optocoupler switching unit 12 serves as a signal sensing and isolation section; its input is connected to the communication bus COM-RXD to sense changes in the current loop state on the communication bus. Its output is connected to the input of the second transistor driving unit 11, converting the sensed current changes into corresponding electrical signals. The second transistor driving unit 11 serves as a signal shaping and driving section; its output is connected to the data receiving terminal (e.g., the RXD pin) of the outdoor unit controller 300, converting the received signal into a level signal recognizable by the outdoor unit controller 300.

[0053] During operation, after the outdoor unit completes data transmission to an indoor unit 200, the communication bus enters a receive waiting state. At this time, the first optocoupler in the selected outdoor unit's transmitting circuit 20 remains on, and the communication bus loop is in a low-impedance state. When the indoor unit 200 returns data to the outdoor unit, the transmitting circuit on the indoor unit 200 side transmits data information by changing the current loop state on the communication bus. Specifically, when the indoor unit 200 transmits data "1", a larger current flows through the communication loop; when transmitting data "0", a smaller current flows through the communication loop. The input terminal of the second optocoupler switching unit 12 is connected in series in the communication bus loop, responding to changes in the loop current. When the communication loop current is large, the optocoupler inside the second optocoupler switching unit 12 is on, and the output terminal is in a low-impedance state; when the communication loop current is small, the optocoupler is off, and the output terminal is in a high-impedance state. In this way, changes in the current on the communication bus are converted into changes in the on / off state of the optocoupler output terminal. The on / off state of the output terminal of the second optocoupler switching unit 12 further controls the conduction and cutoff of the second transistor driving unit 11. The output terminal of the second transistor driving unit 11 is connected to the data receiving terminal of the outdoor unit controller 300, converting the on / off state into corresponding high and low level signals. By reading this level change sequence, the outdoor unit controller 300 can parse the data packets returned by the indoor unit 200 and complete the data reception.

[0054] In this embodiment, the cooperation between the second optocoupler switching unit 12 and the second transistor driving unit 11 enables reliable conversion of the current loop signal on the communication bus to the digital level signal of the controller. Simultaneously, the electrical isolation characteristics of the optocoupler ensure the safety of the communication circuit. This receiving circuit, as the sole receiving channel on the outdoor unit side, serves the return data from each indoor unit 200 in a time-division manner, achieving hardware multiplexing of the receiving circuit.

[0055] Further, see Figure 2 The second transistor driving unit 11 includes a second transistor Q82, a fifth resistor R818, a sixth resistor R819, and a first capacitor C802. The base of the second transistor Q82 is connected to the power supply and the output terminal of the second optocoupler switching unit 12 via the fifth resistor R818. The emitter of the second transistor Q82 is grounded. The collector of the second transistor Q82 is connected to the outdoor unit controller 300 and to the power supply via the sixth resistor R819. The first capacitor C802 is connected in parallel between the collector and emitter of the second transistor Q82.

[0056] In specific implementation, the second transistor driving unit 11 includes a second transistor Q82, a fifth resistor R818, a sixth resistor R819, and a first capacitor C802. It may also include a capacitor C803, a resistor R817, a resistor R820, a diode D83, and a diode D84. The specific connection relationship is as follows: The base of the second transistor Q82 is connected to the power supply via the fifth resistor R818, and this base node is also connected to the output terminal of the second optocoupler switching unit 12. The emitter of the second transistor Q82 is grounded. The collector of the second transistor Q82 serves as the output terminal of this driving unit, directly connected to the data receiving terminal RXD of the outdoor unit controller 300, and simultaneously connected to the power supply via the sixth resistor R819. This power supply can be a 3.3V DC power supply. The first capacitor C802 is connected in parallel between the collector and emitter of the second transistor Q82.

[0057] During operation, when the second optocoupler switching unit 12 is in the off state, its output terminal is in a high impedance state. The +3.3V power supply provides bias current to the base of the second transistor Q82 through the fifth resistor R818, causing the second transistor Q82 to enter the saturation conduction state. At this time, the collector level of the second transistor Q82 is pulled low to near ground potential, and the outdoor unit controller 300 reads the RXD pin as low level. When the second optocoupler switching unit 12 is in the on state, its output terminal is in a low impedance state, pulling the base level of the second transistor Q82 low, causing the second transistor Q82 to enter the off state. At this time, the collector of the second transistor Q82 is pulled up to the +3.3V power supply level through the sixth resistor R819, and the outdoor unit controller 300 reads the RXD pin as high level.

[0058] In this way, the on / off state of the second optocoupler switching unit 12 is converted into high / low level changes on the RXD pin. The outdoor unit controller 300 can parse the data signal returned by the indoor unit 200 by reading this level sequence. The fifth resistor R818 is used to provide bias current to the base when the optocoupler is off, and the sixth resistor R819 acts as a collector pull-up resistor to ensure a definite high level output when the second transistor Q82 is cut off. The first capacitor C802 is connected in parallel at the output terminal to filter out high-frequency interference signals and improve the stability of the received waveform.

[0059] In one embodiment, see Figure 2 The second optocoupler switching unit 12 includes a second optocoupler U820 and a seventh resistor R815. The positive input terminal of the second optocoupler U820 is connected to the power supply, the negative input terminal of the second optocoupler U820 is connected to the communication bus, and the output terminal of the second optocoupler U820 is connected to the input terminal of the second transistor driving unit 11. The seventh resistor R815 is connected in parallel between the positive and negative input terminals of the second optocoupler U820.

[0060] In specific implementation, the second optocoupler switching unit 12 includes a second optocoupler U820 and a seventh resistor R815, as well as a diode D82. The second optocoupler U820 is used to sense the current loop state on the communication bus and achieve electrical isolation. The seventh resistor R815 is a bypass resistor connected in parallel to the input side of the optocoupler. The diode D82 is connected in parallel between the positive and negative terminals of the input terminal of the second optocoupler U820. The specific connection relationship is as follows: the positive terminal (anode) of the input terminal of the second optocoupler U820 is connected to the power supply VCC, and the negative terminal (cathode) of the input terminal of the second optocoupler U820 is connected to the communication bus COM-RXD. Thus, the input side of the second optocoupler U820 is connected in series in the communication bus loop, and its conduction state is directly controlled by the magnitude of the communication loop current. The output terminal of the second optocoupler U820 is connected to the input terminal of the second transistor drive unit 11, i.e., the base node of the second transistor Q82. The seventh resistor R815 is connected in parallel between the positive and negative input terminals of the second optocoupler U820.

[0061] During operation, the current loop state on the communication bus changes according to the data signal sent by the indoor unit 200. When the indoor unit 200 sends data, causing a large current in the communication loop, this current flows through the input side of the second optocoupler U820, illuminating the internal LED and turning on the output side of the second optocoupler U820, pulling the base level of the second transistor Q82 low. When the indoor unit 200 sends data, causing a small current in the communication loop, the current on the input side of the second optocoupler U820 is insufficient to turn it on, the output side remains off, and the base of the second transistor Q82 is pulled high through the fifth resistor R818. The seventh resistor R815 is connected in parallel to the input terminal of the second optocoupler U820, and its function is to provide a bypass current path for the communication loop. By properly setting the resistance value of the seventh resistor R815, the conduction threshold of the second optocoupler U820 can be adjusted, ensuring that the optocoupler reliably turns on when the communication loop current reaches a preset value and reliably turns off when the current is below the threshold, thereby ensuring the accuracy of signal reception.

[0062] In the above manner, the second optocoupler U820 converts the current change on the communication bus into the on / off state change on the output side, thereby controlling the second transistor drive unit 11 to generate the corresponding level signal and complete the data reception function.

[0063] In one embodiment, see Figure 1 and Figure 2 It also includes a communication power supply circuit 40, which is connected to the outdoor unit receiving circuit 10 and the outdoor unit transmitting circuit 20 respectively, and is used to provide operating voltage to the outdoor unit receiving circuit 10 and the outdoor unit transmitting circuit 20.

[0064] In specific implementation, the communication power supply circuit 40 is connected to the outdoor unit receiving circuit 10 and each outdoor unit transmitting circuit 20, respectively, to provide a stable operating voltage for the aforementioned circuits. For details, see... Figure 2 The communication power supply circuit 40 may include an eighth resistor R800, a ninth resistor R809, a second capacitor C800, a first Zener diode ZD80, a second Zener diode ZD81, a first diode D80, and a second diode D80. The eighth resistor R800 is connected at one end to the power supply and at the other end to the positive terminal of the second capacitor C800 and the subsequent power supply node, used to limit the inrush current at power-on. The positive terminal of the second capacitor C800 is connected to the power supply node, and the negative terminal is grounded, used to filter power supply ripple and store energy. The first Zener diode ZD80 and the second Zener diode ZD81 are connected in series across the power supply node and ground, used to clamp the power supply voltage to a preset stable value, providing a stable operating bias for active devices such as optocouplers and transistors in the outdoor unit receiving circuit 10 and the outdoor unit transmitting circuit 20. The first diode D80 and the second diode D80 are connected in series in the communication bus loop, used to prevent reverse voltage or surge signals in the communication loop from damaging the power supply circuit.

[0065] During operation, the external power supply AC_L4 charges the second capacitor C800 through the eighth resistor R800, establishing a stable DC power supply voltage. This voltage, after being regulated by the first Zener diodes ZD80 and ZD81, is supplied to the anode of the input terminal of the second optocoupler U820 in the outdoor unit receiving circuit 10, and the anode of the input terminal of the first optocoupler U830 in each outdoor unit transmitting circuit 20, ensuring that each optocoupler input side receives a stable bias voltage. Simultaneously, this power supply voltage also provides the necessary operating current for each transistor drive unit.

[0066] By setting up the communication power supply circuit 40, a stable and reliable power supply is provided for the outdoor unit receiving circuit 10 and the outdoor unit transmitting circuit 20, ensuring the accuracy and stability of signal transmission and reception in complex electromagnetic environments.

[0067] In summary, the air conditioner indoor and outdoor unit communication circuit provided in this application simplifies the existing technology, which requires multiple outdoor unit transmitting circuits connected in parallel and then connected in series with a single outdoor unit receiving circuit to the same communication bus. Furthermore, a transmitting selection circuit is set to selectively control the conduction of each outdoor unit transmitting circuit. This reduces the number of receiving circuits required in the prior art (the same number as the indoor units) to just one, significantly decreasing the number of optocouplers and peripheral components used in the outdoor unit controller. This effectively lowers hardware material costs, saves layout space on the controller's printed circuit board, and simplifies the circuit structure, thus enhancing the price competitiveness and system reliability of air conditioning products.

[0068] Please see Figure 3The present invention also provides a multi-split air conditioner, which includes an outdoor unit 400, multiple indoor units 200, and an air conditioner indoor-outdoor unit communication circuit 100 as described in any of the foregoing embodiments.

[0069] The communication circuit 100 between the indoor and outdoor units of the air conditioner is located within the outdoor unit 400 and is specifically integrated into the main control board of the outdoor unit 400's controller. Multiple indoor units 200 (e.g., indoor units A, B...N) are connected to the communication bus of the communication circuit 100 via their respective communication cables, thereby enabling data interaction between each indoor unit 200 and the outdoor unit 400. During actual operation, the outdoor unit 400 acts as the communication host, actively initiating communication with each indoor unit 200. The outdoor unit 400 controller 300 sequentially selects the corresponding outdoor unit sending circuit 20 for each indoor unit 200 via the sending selection circuit 30, sending query commands or control data packets to the selected indoor units 200. After receiving the data packet sent by the outdoor unit 400, the selected indoor unit 200 returns status data or response information to the outdoor unit 400 via the same communication bus. The outdoor unit 400 uses a single outdoor unit receiving circuit to receive data returned by each indoor unit 200 in 10 minutes, completing one communication cycle with all indoor units 200.

[0070] Because of the aforementioned communication circuit for indoor and outdoor units with multiplexing receiver circuit, the multi-split air conditioner provided in this embodiment only needs to be configured with one receiver circuit on the outdoor unit side to meet the communication needs with multiple indoor units. This greatly reduces the number of optocouplers and peripheral components required by the outdoor unit controller, lowers the overall hardware cost, simplifies the controller circuit layout, and is conducive to realizing the miniaturization design of the outdoor unit and enhancing the market competitiveness of the product.

[0071] Please see Figure 4 The present invention also provides an air conditioner communication control method, which is applied to the multi-split air conditioner described in the above embodiments. Figure 4 This is a flowchart illustrating the steps of the air conditioner communication control method described above. Figure 4 As shown, the air conditioner communication control method includes the following steps S110-S140.

[0072] S110, Control the transmission gating circuit to select one of the outdoor unit transmission circuits.

[0073] Specifically, the outdoor unit controller outputs a corresponding address code signal to the control terminal of the multi-select chip in the sending selection circuit, so that the channel inside the multi-select chip corresponding to the target indoor unit is turned on, thereby selecting the outdoor unit sending circuit corresponding to that indoor unit.

[0074] S120. Data packets are sent to the corresponding indoor unit through the selected outdoor unit transmitting circuit.

[0075] Specifically, the outdoor unit controller outputs the data packet signal to be sent through the data transmitting terminal TXD, and transmits it through the transmitting gating circuit to the first transistor driving unit in the selected outdoor unit transmitting circuit. This drives the first optocoupler switching unit to turn on or off according to the data signal pattern, thereby loading the data packet onto the communication bus and sending it to the corresponding indoor unit.

[0076] S130. After the data packet is sent, determine whether a return data packet from the indoor unit is received through the outdoor unit receiving circuit within a preset time.

[0077] Specifically, after the data packet is sent, the outdoor unit controller sets the data sending terminal TXD to a high level, keeping the first optocoupler on / off unit in a conducting state, and the communication bus enters a receive waiting state. Subsequently, the outdoor unit controller determines whether a return data packet from the indoor unit has been received through the outdoor unit receiving circuit within a preset time. If a return data packet is received within the preset time, step S140 is executed; if no return data packet is received after the preset time, a communication timeout is determined, and the process jumps to step S140.

[0078] S140. If the returned data packet is received within the preset time, the sending selection circuit is controlled to select the next outdoor unit sending circuit, and the process of sending the data packet to the corresponding indoor unit through the selected outdoor unit sending circuit is resumed.

[0079] Specifically, the outdoor unit controller controls the sending selection circuit to select the next outdoor unit sending circuit, and returns to step S120 to send a data packet to the next indoor unit. This process is repeated in a loop, sequentially polling and communicating with each indoor unit A, B, C, D, E... to achieve time-sharing data exchange between the outdoor unit and all indoor units.

[0080] Using the above method, the outdoor unit controller selectively activates each transmission channel using a transmission gating circuit, and reuses a single outdoor unit receiving circuit to receive data returned by each indoor unit in a time-division manner, thus achieving efficient polling communication between multiple indoor units with simple control logic.

[0081] In one embodiment, such as Figure 5 As shown, before the control of the sending selection circuit to select the next outdoor unit sending circuit, steps S141-S143 are further included.

[0082] S141. Determine whether the returned data packet is complete; S142. If the returned data packet is complete, proceed to the step of controlling the sending selection circuit to select the next external sending circuit; S143. If the returned data packet is incomplete, continue to wait to receive the remaining part of the returned data packet.

[0083] In specific implementation, after determining in step S130 that a return data packet has been received within a preset time, and before executing step S140 to control the sending gating circuit to select the next outdoor unit sending circuit, a step to determine the integrity of the return data packet is also included. Specifically, during the process of receiving the return data packet, the outdoor unit controller continuously verifies the received data. The data packet typically includes fields such as frame header, data length, data content, and checksum. The outdoor unit controller determines whether it has completely received all the data returned by the indoor unit according to the preset data packet format. If the return data packet is determined to be complete, that is, a complete data frame conforming to the protocol has been received, the outdoor unit controller ends the current communication with the current indoor unit, enters step S140, controls the sending gating circuit to select the next outdoor unit sending circuit, and begins communication with the next indoor unit. If the return data packet is determined to be incomplete, that is, some data has not been received, the outdoor unit controller continues to maintain a receiving waiting state, continuously listening to the communication bus, waiting to receive the remaining part of the return data packet until the data packet is completely received or the receiving timeout occurs. If a receiving timeout occurs during the waiting process, the communication with the current indoor unit is also terminated and the system switches to the next indoor unit.

[0084] The above integrity judgment mechanism ensures the accuracy and reliability of data transmission between the outdoor unit and each indoor unit, avoiding communication abnormalities or control errors caused by incomplete data packet reception.

[0085] In summary, the method provided by this invention sequentially selects each outdoor unit's transmitting circuit using a control transmitting gating circuit. The selected transmitting circuit sends data packets to the corresponding indoor unit, and after transmission is complete, a unique outdoor unit receiving circuit waits to receive the data packets returned by the indoor unit. Once the data packet reception is confirmed to be complete or a timeout has occurred, the system switches to the next transmitting circuit for cyclic communication, thus achieving time-sharing polling communication control between the outdoor unit and multiple indoor units. This method, with its simple control logic and multiplexed circuit hardware architecture, effectively reduces system complexity and improves the efficiency and stability of communication between the indoor and outdoor units of a multi-split air conditioner while ensuring communication reliability.

[0086] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A communication circuit for indoor and outdoor units of an air conditioner, characterized in that, include: An outdoor receiver circuit; Multiple outdoor unit transmitting circuits are connected in parallel to each other and then connected in series with the outdoor unit receiving circuit to the same communication bus. Each outdoor unit transmitting circuit is used to connect to an indoor unit. The sending gating circuit has its input terminal connected to the outdoor unit controller, and its multiple output terminals are respectively connected to the control terminals of each of the outdoor unit sending circuits. The transmitting selection circuit is configured to select one of the outdoor unit transmitting circuits according to the control signal of the outdoor unit controller, so that the indoor unit corresponding to the selected outdoor unit transmitting circuit establishes a communication connection with the outdoor unit controller through the communication bus.

2. The communication circuit between the indoor and outdoor units of an air conditioner according to claim 1, characterized in that, Each of the outdoor unit's transmitting circuits includes a first transistor driving unit and a first optocoupler switching unit. The first transistor driving unit is connected to the transmitting gating circuit, and the first optocoupler switching unit is connected to the first transistor driving unit and the communication bus, respectively. The first transistor driving unit drives the first optocoupler switching unit to turn on or off according to the control signal of the transmitting gating circuit, thereby changing the current loop state of the communication bus.

3. The communication circuit between the indoor and outdoor units of an air conditioner according to claim 2, characterized in that, The transmission gating circuit includes a multiplexer chip. The input terminal of the multiplexer chip is connected to the data transmission terminal of the outdoor unit controller. The multiple output terminals of the multiplexer chip are respectively connected to the first transistor driving unit in each of the outdoor unit transmission circuits. The control terminal of the multiplexer chip is connected to the gating control terminal of the outdoor unit controller.

4. The communication circuit between the indoor and outdoor units of an air conditioner according to claim 2, characterized in that, The first transistor driving unit includes a first transistor, a first resistor, and a second resistor. The base of the first transistor is connected to the output terminal of the transmitting gating circuit via the first resistor. The collector of the first transistor is connected to the input terminal of the first optocoupler switching unit. The second resistor is connected in parallel between the base and emitter of the first transistor.

5. The communication circuit between the indoor and outdoor units of an air conditioner according to claim 2, characterized in that, The first optocoupler switching unit includes a first optocoupler, a third resistor, and a fourth resistor. The positive terminal of the first optocoupler's input is connected to the power supply via the third resistor. The negative terminal of the first optocoupler's input is connected to the output of the first transistor driving unit. The output of the first optocoupler is connected to the communication bus. The fourth resistor is connected in parallel to the output of the first optocoupler.

6. The communication circuit between the indoor and outdoor units of an air conditioner according to claim 1, characterized in that, The outdoor unit receiving circuit includes a second transistor driving unit and a second optocoupler switching unit. The input terminal of the second optocoupler switching unit is connected to the communication bus to sense the current loop state on the communication bus. The output terminal of the second optocoupler switching unit is connected to the input terminal of the second transistor driving unit. The output terminal of the second transistor driving unit is connected to the outdoor unit controller to output the received signal to the outdoor unit controller.

7. The communication circuit between the indoor and outdoor units of an air conditioner according to claim 6, characterized in that, The second transistor driving unit includes a second transistor, a fifth resistor, a sixth resistor, and a first capacitor. The base of the second transistor is connected to the power supply and the output terminal of the second optocoupler switching unit via the fifth resistor. The emitter of the second transistor is grounded. The collector of the second transistor is connected to the outdoor unit controller and to the power supply via the sixth resistor. The first capacitor is connected in parallel between the collector and emitter of the second transistor.

8. The communication circuit between the indoor and outdoor units of an air conditioner according to claim 7, characterized in that, The second optocoupler switching unit includes a second optocoupler and a seventh resistor. The positive input terminal of the second optocoupler is connected to the power supply, the negative input terminal of the second optocoupler is connected to the communication bus, the output terminal of the second optocoupler is connected to the input terminal of the second transistor driving unit, and the seventh resistor is connected in parallel between the positive and negative input terminals of the second optocoupler.

9. The communication circuit for indoor and outdoor units of an air conditioner according to any one of claims 1-8, characterized in that, It also includes a communication power supply circuit, which is connected to the outdoor unit receiving circuit and the outdoor unit transmitting circuit respectively, and is used to provide operating voltage to the outdoor unit receiving circuit and the outdoor unit transmitting circuit.

10. A multi-split air conditioner, characterized in that, It includes an outdoor unit, multiple indoor units, and an air conditioner indoor-outdoor unit communication circuit as described in any one of claims 1-9. The air conditioner indoor-outdoor unit communication circuit is located inside the outdoor unit, and the multiple indoor units are respectively connected to the outdoor unit through the air conditioner indoor-outdoor unit communication circuit.

11. A communication control method for an air conditioner, characterized in that, Applied to the multi-split air conditioner as described in claim 10, the method includes: The transmitting gating circuit is controlled to select one of the outdoor unit transmitting circuits; Data packets are sent to the corresponding indoor unit via the selected outdoor unit transmitting circuit; After the data packet is sent, it is determined whether a return data packet from the indoor unit is received through the outdoor unit receiving circuit within a preset time. If the returned data packet is received within the preset time, the sending gating circuit is controlled to select the next outdoor unit sending circuit, and the process returns to the step of sending the data packet to the corresponding indoor unit through the selected outdoor unit sending circuit.

12. The method according to claim 11, characterized in that, Before the control of the transmitting gating circuit to select the next transmitting circuit of the outdoor unit, the method further includes: Determine whether the returned data packet is complete; If the returned data packet is complete, then proceed to the step of controlling the sending strobe circuit to select the next external sending circuit; If the returned data packet is incomplete, continue to wait to receive the remaining part of the returned data packet.

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