Download Display - Service, Support

Glossary
Real Time
Real time means that a system processes external events within a defined time.
Determinism means that a system reacts in a predictable (deterministic) manner.
In industrial networks, both these requirements are important. PROFINET meets these
requirements. PROFINET is implemented as a deterministic real-time network as follows:
• The transfer of time-critical data between different stations over a network within a
defined interval is guaranteed.
To achieve this, PROFINET provides an optimized communication channel for real-time
communication : Real Time (RT).
• An exact prediction of the time at which the data transfer takes place is possible.
• This ensures that unimpeded communication can take place via other standard protocols
in the same network, e.g. industrial communication for the programming device/PC.
→ Real Time
Reduction ratio
The reduction rate determines the send/receive frequency for GD packets on the basis of the
CPU cycle.
Reference ground
→ Ground
Reference potential
Reference potential for the evaluation / measuring of the voltages of participating circuits.
Restart
On CPU startup (e.g. after is switched from STOP to RUN mode via selector switch or with
POWER ON), OB100 (restart) is initially executed, prior to cyclic program execution (OB1).
On restart, the input process image is read in and the STEP 7 user program is executed,
starting at the first instruction in OB1.
Retentive memory
A memory area is considered retentive if its contents are retained even after a power loss
and transitions from STOP to RUN. The non-retentive area of bit memory, timers and
counters is reset following a power failure and a transition from the STOP mode to the RUN
mode.
Retentive can be the:
• Bit memory
• S7 timers
• S7 counters
• Data areas
IM 154-8 CPU Interface Module
Operating Instructions, 12/2006, A5E00860134-01
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