Hardware-based RS485 (radio sensing 485) automatic transceiving control method and circuit

Abstract

The invention relates to an RS485 automatic transceiving control method and circuit. An inverting circuit transmits an inverted TX (transmit) signal to the reset (RST) end of a counting circuit and to the R end of a trigger; a clock generation circuit generates clock frequency fixed to a serial communication Baud rate, and transmits the clock frequency to the CLK (clock) end of the counting circuit; the output end of the counting circuit is connected with the S end of the trigger; and the output end of the trigger is connected with the enable end (DE) of RS485. When the TX signal changes from a higher level value to a lower level value, the circuit transmits a high-level enable signal to the DE port of the RS485 chip to start data transmission; when the TX signal changes from a lower level value to a higher level value, a timer starts and keeps the high-level enable signal of the DE port of the RS485 chip; and the circuit transmits a low-level transmission stop signal to the DE port of the RS485 chip to stop the data transmission if the high-level retention time of the TX signal exceeds the number of frame beats of serial communication information. According to the invention, the RS485 automatic transceiving method and circuit can save the port resources of CPU (central processing unit), and improve communication real-time performance, the interference resistance and the electromagnetic compatibility of the entire system communication.

Description

technical field [0001] The invention belongs to the field of RS485 field bus control, in particular to a hardware-based RS485 automatic transceiver control method and circuit. Background technique [0002] As an electrical specification for data transmission, the suggested standard RS485 is applicable due to its simple network structure interface, convenient control, low cost, strong ability to resist common mode interference, long transmission distance at an appropriate baud rate, and easy network expansion. It is widely used in many different fields, especially in the industrial field as a data transmission link. [0003] The RS485 communication interface circuit adopts differential level transmission and works as half-duplex. Its main function is to convert the TX transmission signal into a differential signal in the communication network through the "transmitter", and also convert the differential signal in the communication network into an RX reception signal through t...

AI Technical Summary

Problems solved by technology

[0006] 1. Occupy the I/O pin resources of the CPU

[0007] 2. There is a certain delay between the assignment of software to the CPU port and the actual enabling of sending data. If the timing of the conversion from sending to receiving is improper, data will be lost and the data frame will be incomplete;

[0008] 3. The reliability of the transition between receiving and sending states is affected by the CPU state of any node, which cannot guarantee that the system has good anti-interference performance

If the CPU of a node on the bus fails, and it is in the high-level state of RS485 transmission, the rest of the nodes will not be able to use the RS485 bus communication normally

[0009] 4. Using this solution in a multi-threaded operating environment with an operating system will increase the difficulty of developing embedded programs

[0012] 2. When this circuit sends a high level, all interfaces on the bus are in the receiving state, and the bus is idle, allowing other interfaces to send data, so it is easy to introduce bus conflicts

[0013] 3. When this circuit sends high level, the transmitter is in a high-impedance state, and there is no driving current, so there is no driving capability, which reduces the anti-interference ability of the interface to a certain extent

[0015] 1. In order to make TX = 1, under the action of the pull-up and pull-down resistors, the bus is at a high level. To achieve this level, the pull-up and pull-down resistors must be comparable to the terminal m

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