rs485接口（RS485 interface）.docVIP

rs485接口（RS485 interface） RS485 interface,.Txt liar too much, fool obviously not enough. I was in charge of kiss your princess in the way to kill Longyou Zhanji River and climbing to the top of the tower. In data communication, computer network and distributed industrial control system, it is often necessary to use serial communication to realize data exchange. At present, there are RS-232, RS-485, RS-422 interface standards for serial communication. RS-232 is the earliest serial interface standard, and has been widely used in short distance (15M) and low baud rate serial communication. In view of the short communication distance and low baud rate of the RS-232 interface standard, the RS-422 interface standard and RS-485 interface standard are proposed to overcome these defects on the basis of the RS-232 interface standard. RS-232, RS-422, and RS-485 interface standards are described in detail below. The RS-232 serial port standard is a single terminal standard for increasing the communication distance at low rate serial communication. RS-232 uses unbalanced transmission, that is, single ended communication. The data signals of the transmitter and receiver are all relative to the earth signals. Therefore, its common mode rejection capability is poor, coupled with the distribution capacitance of twisted pair, the maximum transmission distance is about 15M, the maximum speed is 20KBPS, and it can only support point-to-point communication. In view of the limitation of RS-232 serial port standard, people put forward the standard of RS-422 and RS-485 interface. RS-485/422 uses balanced differential transmit and receive communication: the sender will TTL level signal serial port into a differential signal A, B output, through the cable transmission after the differential signal into a TTL signal at the receiving end. Because the transmission line usually uses twisted pair and differential transmission, so it has a strong ability to resist common mode interference, and the