foreword
(1) Preparing for the principle of microcomputer, here I will share this knowledge point with students who are not serious about class like me.
(2) Although this part has been described in my STM32 serial communication tutorial. But I am worried that some people just want to simply understand this knowledge point, so I will raise it separately.
Three duplexes of serial communication
Serial communication has three duplex modes:Simplex，half duplex，full duplex。
Simplex
（1）Simplex communication only allows transmission in a fixed way. There is only one sender and one receiver. The transmitter and receiver have been established from the beginning and cannot be changed,Data transmission can only be sent from the sender to the receiver.
(2) In simplex communication, two wires are used, one signal wire and one ground wire.
half duplex
(1) The characteristics of half-duplex communication are:Both parties can be both the sender and the receiver, but the problem is that each party can only be in one state during each data transmission.
(2) Half-duplex is the same as simplex, using two wires, one signal wire and one ground wire.
full duplex
(1) Full-duplex is more commonly used,The communication between the sender and the receiver can be carried out at the same time, and both parties can be the sender and the receiver at the same time.
(2) == Full duplex requires the use of three wires! This needs to be clearly distinguished from the first two! ==That is, two signal wires and one ground wire.
(3) Because full-duplex requires the use of three wires, and the two-wire circuit only includes a single data transmission line and a ground wire. Therefore, full-duplex communication cannot be realized in a two-wire circuit.
