Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual page 260

Glossary
Real Time
See 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
• An exact prediction of the time at which the data transfer takes place is possible.
• It is guaranteed that problem-free communication using other standard protocols, for
Reduction factor
The reduction rate determines the send/receive frequency for GD packets on the basis of the
CPU cycle.
Reference ground
See Ground
Reference potential
Voltages of participating circuits are referenced to this potential when they are viewed and/or
measured.
Repeater
See Hub
Restart
On CPU start-up (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.
Glossary-18
defined interval is guaranteed.
To achieve this, PROFINET provides an optimized communication channel for real-time
communication : to: Real Time (RT).
example industrial communication for PG/PC can take place within the same network.
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05