After the electrical signal becomes a readable digital quantity, there are many ways to transmit in the channel, such as parallel transmission and serial transmission, synchronous transmission and asynchronous transmission, Simplex transmission, half-duplex transmission and duplex transmission.
1. Parallel transmission refers to the simultaneous transmission of multi-bit binary data from the sender to the receiver at once. Each data bit has its own transmission channel, which is highly efficient and suitable for short-distance transmission.
2. Serial transmission is divided into two situations: asynchronous transmission and synchronous transmission. If one byte (8 bit) is transmitted, one binary data will be sent at a time, and the same one-byte data will be transmitted bit by bit from low to high bit until the 8-bit transmission is completed.
3. Asynchronous transmission means that the transmitter and receiver have their own independent clocks, and the data bits are divided into groups for transmission. The characters are represented by 8 bits. The sender can send these characters at any time, and the receiver does not know when they will arrive. In order to give the receiving party sufficient response time, each character of asynchronous transmission begins with the beginning of 1 bit, usually the logical value 0, indicating the beginning of the transmission character, then sending the character, and finally sending the stop character, usually the logical value 1, and the length of the stop bit time may be 1 bit, 1.5 bit, 2 Bit. Through the start bit and the stop bit, the receiving end can correctly parse each character to achieve character synchronisation, and the communication rate of the sending and receiving needs to be agreed in advance to achieve bit synchronisation.
4. Synchronous transmission refers to the use of the same clock signal to complete the data transmission by the receiving and receiving parties.
Comparison table of asynchronous transmission and synchronous transmission:
|
No. |
Asynchronous transmission |
Synchronous transmission |
| 1 | It is a character-oriented transmission. | It is a bit-oriented transmission. |
| 2 | Its unit is characters. | Its unit is frame. |
| 3 | It realises character synchronisation through the character start bit and stop bit. | It realises bit synchronisation and frame synchronisation through clock information and frames. |
| 4 | It has lower requirements for timing. | It coordinates the timing through a specific clock line. |
| 5 | It is inefficient. | It is highly efficient |
5. Simplex transmission means that when data can only be transmitted in one direction, one party is the sender and the other party is the receiver. The hardware of the simplex transmission mode is the simplest. The sender only has the sending link, while the receiver only needs the receiving link.
6. Half-Duplex transmission allows two-way transmission of data. Although both parties can send or receive data, they cannot send and receive data at the same time, and only one party can be the sender at the same time. In the Half-Duplex communication mode, both sides of the transmission have a sending link and a receiving link. On the transmission line, the Half-Duplex mode shares a data channel, and the two links are switched to time-sharing multiplexing through the switch.
7. Duplex transmission allows two-way data transmission, and either party can send and receive data at the same time. In duplex mode, the transmission line has two independent data channels. Duplex mode has the highest transmission efficiency, and the corresponding hardware cost is also high.
Post time: Mar-20-2025