Siemens Simatic S7-300 Technical Data Manual page 234

Glossary
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.
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 memory flag bits, timers and
counters is reset following a power failure and a transition from the STOP mode to the RUN
mode.
Retentive can be the:
• Flag bits
• S7 timers
• S7 counters
• Data areas
Router
A router works in a way similar to a switch. With a router, however, it is also possible to
specify which communications nodes can communicate via the router and which cannot.
Communication nodes on different sides of a router can only communicate with each other if
you have explicitly enabled communication via the router between the two nodes.
See Default Router
See Switch
RT
See Real Time
Runtime error
Errors occurred in the PLC (that is, not in the process itself) during user program execution.
Segment
See Bus segment
SFB
See System function block
SFC
See System function
Glossary-18
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05