Siemens Simatic M7-400 Reference Manual page 622

Glossary
Restart
When a CPU starts up (through the use of the mode selector, for example, or
when the power is switched on), either OB 101 (restart), OB 100 (reboot: warm
restart) or OB 102 (cold restart) is processed before cyclic program scanning (OB
1). It is essential for a restart that the CPU is up.
The following applies: All the data areas (timers, counters, memory markers, data
blocks) and their contents are preserved. The ³ process input image is read,
and processing of the STEP 7 user program is continued from the point at which
it was last terminated (STOP, power off).
Other types of startup are the ³ cold restart and reboot (³ warm restart).
Retentivity
Data areas in data blocks, and also timers, counters and memory markers are
retentive when their contents are not lost upon a complete restart or POWER
DOWN.
S7 basic communication
Communication functions integrated in the CPU of the SIMATIC S7/M7/C7 that
can be called by the user. The call is executed in the user program by means of
³ system functions. The user data volume can be up to 76 bytes (small data
volume). S7 basic communication is implemented via ³ MPI.
S7 communication
Communication functions integrated in the CPU of the SIMATIC S7/M7/C7 that
can be called by the user. The call is executed in the user program by means of
³ system function blocks. The user data volume can be up to 64 Kbytes (large
data volume). S7 communication offers a network-independent interface between
devices of the type SIMATIC S7/M7/C7 and the programming device/PC.
Scan time
The scan time is the time required by the ³ CPU to scan the ³ user program
once.
SDB
³ System data block
Segment
³ Bus segment
Glossary-16
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07