Siemens Automation System S7-400 - Manual (Page 224)

Glossary
Glossary-16
Automation System S7-400 Hardware and Installation
A5E00850741-01
V
Varistor
Voltage-dependent resistor
W
Warm Restart
During a CPU startup and before cyclic program processing starts (OB1), either
OB101 (hot restart), or OB100 (restart / warm start), or OB102 is processed first.
Prerequisite for the execution of the “hot restart” function is a backup of all CPU
data.
The data of all data areas ( timers, counters, flags, DBs) are retained. The
process-image input table is read in and the STEP 7 user program processed
starting at the last breakpoint STOP, power failure).
Watchdog interrupt
Generated cyclically within a configurable time pattern by the S7-400 CPU.
Triggers the execution of a corresponding OB. Starting point of the clock cycle is
the operational transition from STOP to RUN.
Work Memory
The work memory is the RAM (Random Access Memory) in the CPU to which the
STEP 7 user program is automatically reloaded from the load memory. The
processor executes the program in the work memory in RUN mode.