Advantages of the P-NET protocol
All nodes that conform to the P-NET standard can be directly connected to the bus and will immediately communicate together, because P-NET uses only one data rate, and only one choice is given for each of the communication layers.
This differs from other standards, which allow many variations on each layer, resulting in many variants that are not able to communicate together.
Any P-NET module, including a master, can be powered down or connected to or disconnected from the bus, without interfering with the rest of the bus system.
Consequently, modules can be exchanged during system operation, and a system can be expanded while the remaining production system continues to run.
The need for configuration of communication parameters in P-NET is much reduced compared with other systems. In slave modules, the P-NET system integrator only has to set the node addresses, and in master modules, he only needs to define the node address and the number of masters.
Therefore, training is reduced and allows any qualified technician to understand and install a P-NET system.
The distributed processing power of a system can be increased, by simply connecting additional masters.
Special procedures have been included in the P-NET standard, making it possible to change the address of a single node on the network, by means of its unique serial number. This allows individual P-NET node addresses to be changed while the system is still running.
Dip switches and other mechanical mechanisms can be avoided, and it is therefore possible to build hermetically sealed P-NET nodes (e.g. IP-67).
When designing a new device for use with P-NET, benefits will be seen from the fact that P-NET can be used to access any logical or physical address within the device, decided upon by the manufacturer.
When a device is implemented with P-NET, both the test procedures performed during the development phase for the application program within the device, and the calibration and maintenance procedures used in the future, can be simplified. P-NET can therefore be used to look inside the device in order to monitor program variables.
The result of a measurement made by a slave, is presented to a master in a pre-processed form, in SI (metric) engineering units. The benefit is significant, since no repetitive scaling or conversion needs to be done by the master(s), leading to considerable savings in processing power. For example, a temperature measurement will be converted to a floating point value by the slave ( IEEE 754 standard), and will be presented to all masters requesting the data in degrees centigrade.
Identifiers used for accessing the physical variable on the network, are mapped via a “SOFTWIRE” list. This list is generated while the application program is being compiled. Therefore, no real time translation is required, leading to very fast data access.
To ensure real time data collection, each frame transmitted on the network is restricted to 56 data bytes. If the requested data length is higher than 56 bytes, it is automaticallydivided into several successive transmissions.