ABB AC 800M, User Manual

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PROFIBUS Technology Terms Section 1 Introduction
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It correspond to IEC Standard 61158-2 and can be also applied to intrinsically safe
installations (EEx i) in Zone 1 / Div.1.
Linking Devices are used to integrate PA bus lines into the PROFIBUS DP network.
This ensures that all information is available in a continuously connected network
through the complete PROFIBUS system (DP and PA).
PROFIBUS Technology Terms
ISO/OSI Reference Model
In accordance with the international ISO/OSI model, a fieldbus protocol can be
uniquely described by means of up to 7 transmission levels. Specific tasks are
assigned to each level in this system. PROFIBUS DP and PROFIBUS PA use only
the first two levels as well as the user interface, which resides in level 7 and where
application functions that can be utilized by the user are determined along with
system and device behavior. Level 1 defines the physical aspect of transmission
(physical layer). This includes, for example, the method of transmission, the
transmission medium, and lengths of lines, while level 2 specifies the bus access
protocol (data link layer).
Bus Access Control
The bus access control (MAC, Medium Access Control) is a specific procedure that
determines at which point in time a PROFIBUS device can send data. While active
devices (master) can start the exchange of information, passive devices (slaves) may
only begin communication when prompted by an active device. A distinction is
made between a controlled, deterministic access procedure with real-time
capabilities (master-slave with PROFIBUS) and a random, non-deterministic access
procedure (CSMA/CD with Ethernet)
Addressing
Each device, connected to a PROFIBUS network, needs an unique address for
selectively identify a field device. For this purpose, PROFIBUS device addresses are
assigned either by an address switch (hard addresses) or by parameter assignment
during commissioning (soft addresses).