Siemens SIMATIC S7-400 Reference Manual page 444

Glossary
Diagnostics
Generic term for → system diagnostics, process fault diagnostics and user-defined diagnostics.
Direct data exchange
Direct data exchange is sometimes also known as direct communication. In direct data
exchange, local input address areas of an intelligent DP slave (for example, CPU 315-2 with
PROFIBUS DP attachment) or a DP master are assigned to a PROFIBUS DP partner. The
intelligent DP slave or the DP master receives the input data that the PROFIBUS DP partner
sends to its DP master via these assigned input address areas.
DP master
A node with master functionality in PROFIBUS DP. A master that conforms to IEC
61784-1:2002 Ed1 CP 3/1 with the DP protocol is known as a DP master. The token allowing
access to the bus is always passed on among the masters. The slaves, in this case DP slaves,
can only react when requested to by a master. The following distinction must be made:
DP master (class 1): handles user data exchange with the DP slaves assigned to it.
DP master (class 2): Provides services such as: reading input/output data, diagnostics, global
control.
DP slave
A → slave operated on PROFIBUS with the PROFIBUS DP protocol is known as a DP slave.
Equipotential bonding
An electrical connection (equipotential bonding conductor) that ties parts of electrical
equipment and extraneous conductive parts to the same or approximately the same potential
to prevent disturbing or dangerous voltages between these parts.
FB
→ Function block
FC
→ Function
Fiber-optic cable
The "force" function overwrites a variable (for example, memory bit, output) with a value defined
by the user.
At the same time, the variable is write-protected so that the value cannot be modified from any
other location (it cannot, for example, be overwritten by the user program). After removing the
programming device, this value is retained.
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S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08