Differences
This shows you the differences between two versions of the page.
| Both sides previous revision Previous revision Next revision | Previous revision | ||
|
en:automation:02-glossary:bacnet-hidden [2020/01/13 12:06] jan_kozak |
en:automation:02-glossary:bacnet-hidden [2020/01/13 12:12] (current) mkudlacek |
||
|---|---|---|---|
| Line 7: | Line 7: | ||
| BACnet operates in a master/slave mode - a feature shared with its closest counterpart Modbus. One or more master devices initiate communication with slave devices and read or write values into them. It is not without interest a device can serve simultaneously as master and slave, allowing it to act as a bridge between different physical interfaces. In this mode, the device effectively functions as a router and relays communication between, for example, BACnet/IP and BACnet MS/TP. | BACnet operates in a master/slave mode - a feature shared with its closest counterpart Modbus. One or more master devices initiate communication with slave devices and read or write values into them. It is not without interest a device can serve simultaneously as master and slave, allowing it to act as a bridge between different physical interfaces. In this mode, the device effectively functions as a router and relays communication between, for example, BACnet/IP and BACnet MS/TP. | ||
| - | The core of BACnet is its method of data exchange. A well-known disadvantage of Modbus is the need to precisely specify devices we want to communicate with. BACnet, on the other hand, allows us to "preview" the device and find out which objects and features are available on it. The "object" is one of the most basic terms we will use throughout the protocol. | + | The core of BACnet is its method of data exchange. A well-known disadvantage of Modbus is the need to precisely specify devices we want to communicate with. BACnet, on the other hand, allows us to "discover" the device and find out which objects and properties are available on it. The "object" is one of the most basic terms we will use throughout the protocol. |
| - | Each BACnet device shares information through objects, which take the form of a definition similar to a data point. That means a single object represents one specific input/output, one operating value of the device etc. Each object has its properties, eg. real values of the said object. To make our work with an unknown device easier, the standard defines a list of properties each object must implement. Among these "mandatory" features is, for example, a property name, its unique numerical identification and its current value. Other properties may include a quantity the current value represents, its threshold values etc. Currently, there are over 500 of such specified properties and many more can be defined freely by device vendors. | + | Each BACnet device shares information through objects, which take the form of a definition similar to a data point. That means a single object represents one specific input/output, one operating value of the device etc. Each object has its properties, eg. real values of the said object. To make our work with an unknown device easier, the standard defines a list of properties each object must implement. Among these mandatory properties is, for example, a property name, its unique numerical identification and its current value. Other properties may include a quantity the current value represents, its threshold values etc. Currently, there are over 500 of such specified properties and many more can be defined freely by device vendors. |
| Modbus users are also probably used to communicate through functions for reading or writing data into registers and coils. BACnet designates these functions as services and defines over 30 of them. However, there are only few services each device must support (and which you will encounter most frequently). These are services for looking up devices in the network (the Who-is service), describing its objects (the Who-has service) and read/write functions for editing property values (Read-property + Write-property). | Modbus users are also probably used to communicate through functions for reading or writing data into registers and coils. BACnet designates these functions as services and defines over 30 of them. However, there are only few services each device must support (and which you will encounter most frequently). These are services for looking up devices in the network (the Who-is service), describing its objects (the Who-has service) and read/write functions for editing property values (Read-property + Write-property). | ||
| - | However, it is worth noting that most of BACnet definitions are well-hidden. This allows the BACnet users to focus on the most important task - to start up the device. BACnet devices can be easily added or swapped, while the protocol guarantees interoperability of devices from various vendors. | + | However, it is worth noting that most of BACnet definitions are well-hidden. This allows the BACnet users to focus on the most important task - to integrate the device into the network. BACnet devices can be easily added or swapped, while the protocol guarantees interoperability of devices from various vendors. |
