PLC transmission rate and line communication method - Database & Sql Blog Articles

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1. Transmission rate

The transmission rate refers to the amount of information transmitted per unit time, which is the main indicator for measuring system transmission. Three rates are defined in the data transmission: modulation rate, data signal rate, and data transmission rate.

(1) Modulation Rate The modulation rate, also known as the symbol rate, is the transmission rate of the pulsed signal after modulation. That is, the number of times the signal is modulated in a unit of time during the modulation process, that is, the number of modulations that can be modulated per unit time. The unit is baud, which is usually used to indicate the rate at which signals are transmitted between modems.

(2) Data signal rate The data signal rate is the amount of information passing through the channel per unit time, expressed in bits per second (bit/s). Modulation Rate and Data Signal Rate When serially transmitting a binary modulated signal, the rates of the two are numerically the same.

Usually, the modulation rate and the data signal rate are not strictly distinguished, but they are generally referred to as the transmission rate (also known as the baud rate), and the unit is baud, that is, the transmission per second is a binary digit, using bit/s. Said.

(3) Data transmission rate The data transmission rate refers to the amount of data transmitted per unit time. The unit of data amount can be bits, characters, etc., usually in characters per minute. For example, when a transmission circuit with a data signal rate of 1800 bit/s is used, when the ASCII code data is transmitted in an asynchronous transmission mode, the data transmission rate is

Data transmission rate = (1800 × 60) / (8 + 2) characters / min: 10800 characters / mm

In the formula, "2" in the denominator refers to a start bit and a stop bit added in one character bit.

2. Line communication method

The data is transmitted on the communication line with directionality. According to the direction in which the data is transmitted at a certain time, the line communication mode can be divided into simplex communication, half-duplex communication and full-duplex communication.

(1) Simplex communication mode Simplex communication means that the transmission of information always remains in the same direction, but cannot be reversed, as shown in Figure 1-3. One station can only act as the sender, and station B can only act as the receiver.

(2) Half-duplex communication mode Half-duplex communication means that information flow can be transmitted in two directions, but only one direction is transmitted at the same time, as shown in Figure 1-4. Among them, station A and station B have the function of sending and receiving, but only one transmission line, or station A sends station B.

Receive; or station B sends a station to receive.

Figure 1-3 Simplex communication

Figure 1-4 Half-duplex communication

(3) Full-duplex communication mode Full-duplex communication can be sent and received simultaneously in the same direction, as shown in Figure 1-5. Both the station A and the station B can send data while receiving data.

Figure 1-5 Full-duplex communication