In the industrial control, the star network has a central control unit, which is connected to the central host system by a plurality of terminal control processors, enabling centralized control. Its central controller as a site has the ability to process information and data transfers, that is, to perform processing functions or to convert information from one place to another.
The surrounding sites usually use the polling interrupt method to apply for services to the central processor: it in turn asks each site around whether there is information to be sent. If so, the central station's communication control unit processes the device centrally until no information is sent or transferred to Handle on other devices.
Advantages: Independent operation, failure of a single site, does not affect the information transmission and dialogue of other sites.
Disadvantages: Poor reliability, the failure of the central control unit will become fatal, the connection and connection equipment are also more, the cost is expensive, and it is not as simple as expanding a new site.
The tree-shaped hierarchical network is an extension of the star network, which has a central control unit and several sub-controllers. The lowermost part is some terminal equipment, and there is a relatively obvious hierarchical relationship between the processors. Usually, the lowermost processor performs the data collection function, the intermediate processor performs the data processing and control functions, and the high-level processor is based on The information provided by the subordinate processor performs comprehensive processing functions to make management decisions.
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