Method for adaptively controlling transmitting and receiving directions of RS485 chip by aid of FPGA (field programmable gate array)

Abstract

The invention discloses a method for adaptively controlling transmitting and receiving directions of an RS485 chip by the aid of an FPGA (field programmable gate array). The method is mainly implemented by the aid of a data transmitting and receiving master control CPU (central processing unit), the adaptive direction control core FPGA, the RS485 chip and a peripheral circuit. The method includes enabling the FPGA and the RS485 chip to simultaneously receive TXD (transmit data) signals transmitted by the CPU, and transmitting RST (reset) signals transmitted by the FPGA to transmitting and receiving direction control pins of the RS485 chip; enabling the FPGA to quickly judge whether the RTS signals are high-level signals or low-level signals according to variation of level of the received TXD signals, enabling the RS485 chip to receive signals when the RTS signals are the low-level signals, and enabling the RS485 chip to transmit signals when the RTS signals are the high-level signals so as to control the transmitting and receiving directions of the RS485 chip. The method has the advantages that designs of hardware principles and improvement on existing hardware can be facilitated, algorithms of the FPGA are stable and reliable and are easy to implement, and accordingly the data communication stability and reliability of RS485 buses can be effectively guaranteed.

Description

technical field [0001] The invention belongs to the technical field of digital communication, and in particular relates to a method for adaptively controlling the sending and receiving direction of an RS485 chip by an FPGA (that is, a field programmable gate array). Background technique [0002] RS485 communication is widely used in the information exchange between the master station and each master-slave station. How to control the direction of RS485 communication is very important to realize the stable communication of RS485. There are mainly the following methods to achieve: (1) Use the I / O port of the CPU for control. This method has strong driving ability, but it needs software cooperation; (2) There is a CPU with RTS control pin (that is, request to send control pin pin) can be directly used to control the sending and receiving direction of RS485. It has strong driving ability and does not need software cooperation, but not all CPUs have this function, and generally th...

AI Technical Summary

Problems solved by technology

There are mainly the following methods to achieve: (1) Use the I / O port of the CPU for control. This method has strong driving ability, but it needs software cooperation; (2) There is a CPU with RTS control pin (that is, request to send control pin pin) can be directly used to control the sending and receiving direction of RS485. It has strong driving ability and does not need software cooperation, but not all CPUs have this function, and generally there are not many pins of this type. When multiple serial ports are required for communication, it will Not enough; (3) Make the half-duplex RS485 transceiver realize the self-transmitting function, generate the RTS signal through the TXD (data output transmission) signal through the inverter, and increase the pull-up and pull-down resistors between the A and B terminals to achieve it. The method is simple to implement and low in cost, but the driving ability is weak and the anti-interference ability is not enough; (4) On the basis of method (3), the falling edge of TXD before passing through the inverter is delayed, and the driving ability is increased to a certain extent , but the anti-interference ability is still not good under the harsh external environment

[0003] RS485 chip self-receiving is a common usage nowadays, but the communication mechanism of this automatic control direction has weak driving ability. In the case of harsh environment and serious interference, this communication method will cause code errors and cause communication errors.

Images