Logical control layer communication protocol

Communication protocol, but it is hard to define its scope literally. This protocol may be a network protocol or a communication protocol. The communication protocol we discuss here is the main, slave network which is based on RS-422 or RS-485 bus at the bottom of the measurement and control system, it is much simpler than the network communication protocols (such as OSI and TCP/IP protocols) of computer network systems, in particular, the hierarchical structure of network communication protocols is helpful ｡

Communication protocols are rules or standards established for the exchange of network data, can also be understood as a series of agreements between the parties (Parties). For example, both parties agreed that: All use RS-485 interface, all initialization settings are set to 9 600 Potter, 7-Bit Data bit, 1-bit stop bit, and odd verification is used ｡

This actually follows two levels of Protocols: Physical Layer-specifying physical connections, electrical properties, data link layer-specifying the composition of frames and error control ｡

These two layers can be used to transfer characters. As for the meaning of some (or some) characters, further agreements are required on the answers required by the other party. Such agreements are based on the physical layer and the data link layer, this may be referred to as the logical control layer protocol. For the master and slave networks at the underlying layer of the measurement and control system, the communication protocol can have these three layers. Once the communication protocol is formulated, all parties must abide by it, different parties can use different machines or different programming languages to write communication programs ｡

The following is an example of the communication protocol (logical control layer) between the host computer and the single-loop controller )｡

A single loop controller can be used to control a loop (including a controlled object, generally, it consists of a single-chip microcomputer and a small number of external circuits. Figure 12.30 shows that a single-loop controller is used to control the water level of a container ｡