Constant bus cycle time
Constant bus cycle time means a DP bus cycle accurate to a few microseconds that can be
configured in STEP 7.
CP
→ Communications processor
Data block
Data blocks (DBs) are data areas in the user program that contain user data. There are shared
data blocks that can be accessed by all logic blocks and there are instance data blocks
assigned to a specific FB call.
Declaration
Definition of variables (for example parameters or local data of a block) with name, data type,
comment etc.
Default (setting)
The default is a practical basic setting that is always used when no other value is specified.
Destruction limit
Limit of the permitted input voltage/current. If this limit is exceeded, the measurement accuracy
can deteriorate. If the destruction limit is exceeded considerably, the internal measuring
circuitry can be destroyed.
Diagnostic buffer
The diagnostic buffer is a buffered memory area on the CPU in which the diagnostic events
are entered in the order in which they occur.
The user can read the precise cause of the problem from the diagnostic buffer with STEP 7
(PLC -> Module Information menu command) and start troubleshooting measures.
Diagnostic data
All diagnostic events that occur are collected on the CPU and entered in the → diagnostic
buffer. If an error OB exists, this is started.
Diagnostic interrupt
Diagnostics-compliant modules signal detected system errors to the → CPU using diagnostic
interrupts. If a diagnostic interrupt occurs, the CPU calls OB82.
Glossary
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
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