We often see RS485 and MODBUS written together, what are their differences and connections?
RS485 is a physical interface, simply put, hardware.
MODBUS is an international standard communication protocol for exchanging data between devices of different manufacturers (generally for industrial use); the so-called protocol, which can also be understood as the "language" someone said above, is simply software.
MODBUS was invented by MODICON (now a brand of Schneider Electric) in 1979 and was the world's first true bus protocol for industrial sites.
The MODBUS network is an industrial communication system consisting of programmable controllers and computers with intelligent terminals connected by common or local dedicated lines. Its system architecture includes both hardware and software. It can be used for various data acquisition and process monitoring applications.
The MODBUS network has only one host, from which all communications are sent. The network can support up to 247 remote slave controllers, but the actual number of slaves supported is determined by the communication equipment used. With this system, each PC can exchange information with the central host without affecting the execution of each PC's own control tasks.
RS485 belongs to the wired transmission, so we have to hardware transmission medium, the actual two lines on the two lines is the actual transmission of the same signal, but the transmitter side of the signal in two, but in the receiving end will restore it to the original signal.
As for MODBUS is only one kind of communication protocol, just like Chinese and English, is a language of communication, a language of communication between machines. So there must be a bridge of communication before the exchange, that is to say, the transmission medium 485 or 232 or other electrical rules, the same protocol can be used in different ways of transmission media such as 485 or 232 but the same transmission line can not exist at the same time two protocols.