Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 - Manual (Page 219)

Glossary
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05
Glossary-3
Compress
The PG online function "Compress" is used to rearrange all valid blocks in CPU RAM in one
continuous area of user memory, starting at the lowest address. This eliminates
fragmentation which occurs when blocks are deleted or edited.
Configuration
Assignment of modules to module racks/slots and (e.g. for signal modules) addresses.
Consistent data
Data which are related in their contents and not to be separated are referred to as consistent
data.
For example, the values of analog modules must always be handled consistently, that is, the
value of an analog module must not be corrupted as a result of read access at two different
points of time.
Counters
Counters are part of CPU system memory. The content of "Counter cells" can be modified by
STEP 7 instructions (for example, up/down count.)
CP
See Communication processor
CPU
Central processing unit = CPU of the S7 automation system with a control and arithmetic
unit, memory, operating system, and interface for programming device.
Cycle time
The cycle time represents the time a CPU requires for one execution of the user program.
Cyclic interrupt
See Interrupt, cyclic interrupt
Data block
Data blocks (DB) are data areas in the user program which contain user data. There are
global data blocks which can be accessed by all code blocks, and instance data blocks
which are assigned to a specific FB call.
Data, static
Static data can only be used within a function block. These data are saved in an instance
data block that belongs to a function block. Data stored in an instance data block are
retained until the next function block call.