In the past, PC and smart device communications more than RS232, RS485, Ethernet, etc., depending on the interface specifications of the device. However, RS232, the RS485 can only represent the physical media layer and link layer of the communication. If you want to implement two-way access to data, you must write a communication application yourself, but most of this program cannot comply with the ISO / OSI specification, you can only implement More than a single function, for a single device type, the program does not have versatility. In the equipment network coupled to the RS232 or RS485 device, if the number of devices exceeds 2, the RS485 must be used to communicate media. The RS485 network must be used to interwork information only through the "master" device to be implemented. The master device is usually a PC, and only one master device is allowed in such a device network, and the rest is from the SLAVE device. Fieldbus technology is based on ISO / OSI model, with complete software support systems, can solve bus control, conflict testing, link maintenance. Fieldbus equipment automatically generates network, no master / slave equipment or allows multiple owners to exist. The products of different manufacturers can be interchanged in the same level, and the devices have interoperability.
Where is the difference between 485 and 422? 1. What is the full duplex, what is half-duplex: full-duplex: At the same time, it can only be received again. Half-duplex: It is impossible to send both the same time, it is time to send. Full-duplex requirements: Received a separate channel with each other. Can be used to implement communication between two stations and the star network, ring network. Not available for bus network. Half-duplex requirements: Transceiver can share the same channel, which can be used for all topologies. LAN is most commonly used for bus networks. Half duplex data rate is theoretically half of the whole work. 2. Find the RS422 and RS485: RS422 has at least one differential transmission port and differential receiving port. When the two nodes communicate, the send port of one party is connected to the other receive port. Two pairs of lines are required. The RS422 cannot be directly used for the direct interconnection of three electricity, and of course, it is not possible to connect directly to the bus. The differential transmission port of the RS485 is associated with its own differential reception port, and the multipoint between the multi-point is only a pair of lines. If the transmitting port of RS422 is as follows with its receiving port, it becomes RS485.3, and the RS422 can be connected to RS485, so their electrical parameters must be identical. 4, you need to say, many people often score the RS232, RS422, RS485 as a communication or network protocol, which is very embarrassing, in fact, they are only a mechanical and electrical interface standard for communication (top more is the network protocol Physical level).
