How Do Distinguish Between RS232, RS485, RJ45, and Modbus?(2)

RS422 interface and RS232 interface:

The RS422 interface and the RS232 interface are full-duplex interfaces, while the RS485 is a semi-two-way work interface.

For the semi-two-way work interface, it is obvious that there is an initiator of communication, so the RS485 interface and network must have a master station and several slave stations, and the number of slave stations is also specified. Typically, the number of slaves is 32.

The relationship between the RS485 master station and the slave station seems to be only the difference in the communication work system.

Bus connection problem.

Let's look at the bus connection problem again. Let's take the power supply as an example. We can draw a main line from the power supply, and then parallel several branches and send them to several loads respectively.

If we use the same method to lead out the RS485 communication line, is it feasible? the answer is negative. We must lead a line from the communication master to the first communication substation, and then lead a second line from the first substation to the second substation, and so on until the last substation. At the terminal of the communication line, a terminating resistor is also required. On this communication line, if an open circuit occurs at any point, the communication on the subsequent communication link is also interrupted. This wiring method is vividly called the daisy-petal connection method, or the chain connection method, and the wiring method of the power supply is called the star connection method.

We found that from the electrical wiring, the links are in parallel. But from the communication point of view, the link is a chrysanthemum petal and belongs to an orderly connection one after another.

Now we can summarize:

The bus network connection method of RS485 must be the connection method of chain daisy petals and belongs to the half-duplex communication method. RS232 is a point-to-point wiring method, which belongs to full-duplex communication. Whether it is an RS232 interface or an RS485 interface, they must comply with the communication protocol of the physical layer.