How Do Distinguish Between RS232, RS485, RJ45, and Modbus?(1)
Imagine a DC power supply, its output socket interface has three pins, which are positive, negative, and ground. Correspondingly, the plug of the load should also have three pins corresponding to the power supply side, so that the power supply can be obtained correctly.
Note that there are three conditions that must be met:
The first is that the shape, size, diameter, and length of the pins of the plug and socket must correspond one by one, otherwise, the plugging operation cannot be completed. This point specifies the physical structure and pinout of the plug combination.
The second is that the output voltage value of the power supply must meet the demand value of the load side, otherwise, the requirements of the electrical parameters cannot be fulfilled. This determines the level specification of the plug combination.
The third is that the output impedance of the power supply must match the input impedance of the load, otherwise, a perfect power supply cannot be achieved. This determines the working nature of the power supply.
These three points are actually the normative agreement on the physical level of the power plug combination.
Look at the communication interface again. In the ISO/OSI model of computer information exchange, the physical layer is the lowest layer (layer 1). It specifies the mechanical shape of the interface, the definition of the interface pins, the interface level and the byte format.
The byte format here refers to how many data bits in a byte, how many start bits/stop bits, and how many parity bits. Generally, a byte has 8 data bits, 1 start bit (stop bit), and 1 parity bit.
Let's look at the working system of the communication interface and the communication network.
When we hang up the phone with our mobile phone, we find that both parties can answer the call while talking, which is called a two-way work system. If you can't listen when speaking, and can't speak when answering, but either party has the ability to speak and listen, that is, the type of walkie-talkie talk, this is called a semi-two-way work system.
