3BHB007211R0101 ABB

Serial communication is divided into simplex and duplex according to the transmission direction of information between devices.

Simplex communication can only send or receive data in one direction.Information in duplex communication can be transmitted in both directions,and each station can either send or receive data.

The duplex mode is further divided into two modes:full duplex and half duplex.The transmission and reception of data are transmitted by two or two different data lines respectively.Both parties of the communication can receive and send information at the same time.This transmission method is called full-duplex mode;the same line or the same group of lines is used.To receive and send data,both parties in the communication can only send or receive data at the same time.This transmission method is called half-duplex mode.Half-duplex and full-duplex communication are often used in PLC communication.

串行通信按信息在设备间的传送方向又分为单工、双工两种方式。

单工通信方式只能沿单一方向发送或接收数据。双工通信方式的信息可沿两个方向传送，每一个站既可以发送数据，也可以接收数据。

双工方式又分为全双工和半双工两种方式。数据的发送和接收分别由两根或两组不同的数据线传送，通信的双方都能在同一时刻接收和发送信息，这种传送方式称为全双工方式；用同一根线或同一组线接收和发送数据，通信的双方在同一时刻只能发送数据或接收数据，这种传送方式称为半双工方式。在PLC通信中常采用半双工和全双工通信。