CN201114169Y - Serial communication interface isolation driving circuit - Google Patents

Abstract

The utility model relates to a communication interface circuit, in particular to a serial communication interface isolation driving circuit which can power on equipment on a serial bus online but cannot affect the bus in case of power supply failure. The circuit comprises a photoelectric coupler, a serial communication driving chip and a reverser, wherein an output of the photoelectric coupler is connected to an input terminal of the reverser, an output terminal of the reverser is connected with a direction control terminal of the serial communication driving chip, an input terminal and an output terminal of the photoelectric coupler adopt different power supplies so as to keep the direction control terminal of the serial communication driving chip in a receiving state at a low level and in a sending state at a high level. In case the input terminal of the photoelectric coupler was power-off or presents a high level during reset, the reverser reverses the output to a low level signal, forcing the communication direction of the serial communication driving chip to be in a receiving state so as to protect the serial communication network.

Description

Serial communication interface isolation driving circuit

technical field

The utility model relates to a communication interface circuit, in particular to a serial communication interface isolation driving circuit which prevents the equipment on the serial bus from being affected by the bus when it is powered on and the power supply fails.

Background technique

The half-duplex serial communication driver chip is a chip widely used in the field of communication. Taking the RS485 communication interface as an example, a main application method is: the CPU communication direction control signal is directly connected to the direction control terminal of the RS485, and the direction control terminal of the RS485 uses a low-level control chip to receive the communication signal, and a high-level control chip Controls the sending of communication signals. Since the RS485 bus can only allow one driver port to be in the sending state at the same time, the device on the bus cannot be in the sending state when it is driven or faulty, especially when the device is connected online, because some CPU ports show a high level after reset state, while the direction control terminal of the RS485 driver chip is in the sending state at a high level, so when starting, it will cause multiple devices on the bus to be in the sending state, thereby causing a bus failure.

Another main application method is: the CPU power supply that sends the control signal and the RS485 power supply are isolated by a photocoupler (hereinafter referred to as the photocoupler), and the communication direction control signal sent by the CPU is connected to the communication direction control signal of the RS485 through the photocoupler. When the CPU, which is the sending end of the direction control signal, is powered off, the output end of the optocoupler is a high-level signal, which makes the RS485 in the sending state, and also causes failures to the RS485 bus.

Utility model content

The utility model overcomes the above-mentioned shortcomings, and provides a serial communication interface isolation drive circuit with a relatively simple structure, in which the bus equipment is powered on and the power failure does not affect the bus.

The technical solution adopted by the utility model to solve the technical problem is: a serial communication interface isolation drive circuit, including a photoelectric coupler and a serial communication drive chip, the input end of the photocoupler is used to receive the communication sent by the CPU Direction control signal, the serial bus is used to receive and send bus signals, and also includes an inverter, the output of the photocoupler is connected to the input of the inverter, and the output of the inverter is connected to the inverter The direction control terminal of the serial communication driver chip is connected, and the input terminal and output terminal of the photocoupler adopt different power sources respectively.

The input end of the optocoupler and the CPU can use the same power supply, and the output end of the optocoupler can use another same power supply as the inverter and the serial communication driver chip.

The serial communication driver chip may be an RS485 communication driver chip.

The optocoupler may be a high-speed optocoupler.

The utility model arranges a reverser at the output end of the optocoupler, so that the direction control end of the serial communication drive chip is in the receiving state when it is low level, and is in the sending state when it is high level. When the input end and output end of the optocoupler In the case of using different power sources, if the input terminal of the optocoupler connected to the CPU is a power failure or reset, the input terminal of the optocoupler presents a high level, and the output terminal of the optocoupler is also at a high level. The reverse output becomes a low-level signal, and the low-level signal forces the communication direction of the serial communication driver chip to be in the receiving state, which will not cause damage to the serial communication bus and play a significant role in the serial communication network. Protective effects.

Description of drawings

Fig. 1 is the circuit schematic diagram of the utility model.

Detailed ways

As shown in Fig. 1, it is the circuit principle diagram of a kind of preferred embodiment of the utility model, what the serial communication drive chip in the present embodiment adopts is the RS485 chip, wherein the communication direction control signal of CPU U4 communicates with a RT_Ctrl end through RT_Ctrl end The input end of the optocoupler U1 is connected, the output end of the optocoupler U is connected to the input end of an inverter U2, and the output signal of the inverted signal received by the inverter U2 is sent to the The direction control terminal of the RS485 chip U3, the input terminal of the CPU U4 and the optocoupler U1 use the same power supply VCC, and the output terminal of the optocoupler U1, the inverter U2 and the RS485 chip U3 use another power supply VCC1.

According to the above structure, since the output communication direction control signal of the optocoupler U1 is reversed by the inverter U2 to control the signal transmission direction of the RS485 U3, the direction control terminal of the serial communication driver chip is in the receiving state when it is at a low level. state, it is in the sending state when it is high, when the input and output of the optocoupler use different power sources, if the input of the optocoupler connected to the CPU is a power failure or reset, the input of the optocoupler presents a high level , the output terminal of the optocoupler is also at a high level, and the reverse output of the inverter becomes a low level signal, and the low level signal forces the communication direction of the serial communication driver chip to be in the receiving state. It will cause damage to the serial communication bus and play an obvious role in protecting the serial communication network.

The above is a detailed introduction to the serial communication interface isolation drive circuit provided by the utility model. In this paper, specific examples are used to illustrate the principle and implementation of the utility model. The description of the above embodiments is only used to help understand the utility model. new method and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the utility model, there will be changes in the specific implementation and application scope. In summary, the contents of this specification should not It should be understood as a limitation of the present utility model.

Claims (4)

1. A serial communication interface isolation drive circuit, comprising a photocoupler and a serial communication driver chip, the input of the photocoupler is used to receive the communication direction control signal sent by the CPU, and the serial bus is used to receive . Sending a bus signal, characterized in that: it also includes an inverter, the output of the photocoupler is connected to the input of the inverter, and the output of the inverter is connected to the serial communication drive chip. The direction control terminal is connected, and the input terminal and output terminal of the photocoupler adopt different power supplies respectively. 2. The serial communication interface isolation drive circuit according to claim 1, characterized in that: the input terminal of the photocoupler and the CPU adopt the same power supply, and the output terminal of the photocoupler is opposite to the The device and the serial communication driver chip use the same other power supply. 3. The serial communication interface isolation drive circuit according to claim 1 or 2, characterized in that: the serial communication drive chip is an RS485 communication drive chip. 4. The serial communication interface isolation drive circuit according to claim 1 or 2, characterized in that: the optocoupler is a high-speed optocoupler.

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