Siemens SIMATIC S7-400 Reference Manual page 446

Glossary
Functional grounding
Grounding with the sole purpose of ensuring the intended function of the electrical equipment.
Functional grounding, short-circuits interfering voltages that would otherwise have an
unacceptable influence on the equipment.
Fuse blown
Parameter in STEP 7 for digital output modules. When the parameter is enabled, the blowing
of one or more fuses is detected by the module. With suitable parameter assignment, a →
diagnostic interrupt is triggered.
Grounding
Grounding means connecting an electrically conductive part to the ground electrode (one or
more conductive parts that make good contact with ground) via a grounding system.
Hardware interrupt
A hardware interrupt is triggered by interrupt-triggering modules due to a particular event in
the process (violation of a limit value, module has completed the cyclic conversion of its
channels).
The hardware interrupt is signaled to the CPU. In keeping with the priority of this interrupt, the
corresponding → organization block is then executed.
Hold last value (HLV)
The module retains the last value output prior to changing to STOP mode.
Hot restart
When a CPU starts up (for example as a result of activating the mode selector or turning on
the power), cyclic program execution (OB1) initially processes either OB101 (hot restart),
OB100 (cold restart: hot restart) or OB102 (cold restart). Backup of the CPU is absolutely
necessary for a hot restart.
The following applies: all data areas (timers, counters, memory bits, data blocks) and their
content are retained. The → process image of the inputs is read in and the execution of the
STEP 7 user program is continued from the point at which it was last stopped (STOP, power
down).
The other startup modes available are → cold restart and → warm restart.
I/O bus
Part of the → backplane bus in the automation system optimized for fast exchange of signals
between the CPU or CPUs and the signal modules.
Useful data (for example, digital input signals of a signal module) and system data (for example
default parameter data records of a signal module) is transferred over the I/O bus.
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S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08