RS485 bus standard is a very widely used bidirectional, balanced transmission standard interface in the industry (attendance, monitoring, data acquisition system), supports multi-point connection, allows the creation of a network of up to 32 nodes; the maximum transmission distance of 1200m, supports 1200 m It is a high-speed transmission of 100kb / s, and has strong anti-interference ability. It is very simple to route only two wires.
The RS485 communication network interface is a bus-type structure. The upper computer (in the case of a personal computer) and the lower computer are all hung on the communication bus. The communication protocol of the RS485 physical layer consists of the RS485 standard and the multi-computer communication mode of 51 single chip computers. Because rs-485 / 'target =' _ blank '> RS-485 is developed from RS-422, so rs-485 /' target = '_ blank'> RS-485 many electrical regulations are similar to RS-422 . If balanced transmission methods are used, it is necessary to connect termination resistors on the transmission line. RS-485 can be used in two-wire and four-wire modes, and the two-wire system can realize true multi-point two-way communication.
The following describes the following standards defined by the RS485 communication interface
1. The British symbols are TDA (-), TDB (+), RDA (-), RDB (+), GND
2. The American signs are Y, Z, A, B, GND
3. The Chinese symbols are TXD (+) / A, TXD (-) / B, RXD (-), RXD (+), GND
The rs485 two-wire is generally defined as:
"A, B" or "Date +, Date-"
It is often said: "485+, 485-"
The rs485 four-wire is generally defined as:
"Y, Z, A, B,"
Generally, there is no fixed standard for the rs485 protocol connector, and the pin sequence and pin function may be different according to different manufacturers, but the official will generally provide a product manual, and the user can refer to the related rs485 pin diagram definition or pin diagram
"Rs232 to rs485 circuit diagram"
In the above figure, rs232 to rs232 in the rs485 circuit (max232 can play the same role but it is more expensive). It plays the role of converting the rs232 interface level of the pc side, and then converts the signal from the max485 chip to the 485 level by AB two. Line output, if the signal is connected to the twisted pair signal rs485 bus interface, the communication distance is at least 1 km away.
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