Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 - Manual (Page 65)

Memory concept
4.1 Memory areas and retentivity
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05
4-3
Retentive data in RAM
Therefore, the contents of retentive DBs are always retentive at restart and POWER
ON/OFF.
CPUs V2.1.0 or higher also support volatile DBs (the volatile DBs are initialized at restart of
POWER OFF-ON with their initial values from load memory.)
See also
Properties of the Micro Memory Card (MMC) (Page 4-9)
4.1.3 Retentivity of memory objects
Retentive behavior of memory objects
The table below shows the retentive behavior of memory objects during specific operating
state transitions.
Table 4-2 Retentive behavior of memory objects (applies to all CPUs with DP/MPI-SS
(31x-2 PN/DP)
Memory object Operating state transition
POWER ON /
POWER OFF
STOP →
RUN
CPU memory
reset
User program/data (load memory) X X X
• Retentive behavior of DBs for CPUs
with firmware < V2.1.0
X
X
–
• Retentive behavior of DBs for CPUs
with firmware >= V2.1.0
Can be set in the properties of the DBs
in STEP 7 V5.2 + SP1 or higher.
–
Flag bits, timers and counters configured as
retentive data
X X –
Diagnostics buffers, operating hour
counters
X X X
MPI address, transmission rate
(or also DP address, transmission rate of
the MPI/DP interface of CPU 315-2 PN/DP
and CPU 317, if these are configured as
DP nodes.)
X X X
x = retentive; – = not retentive
Retentive behavior of a DB for CPUs with firmware < V2.1.0
For these CPUs, the contents of the DBs are always retentive at POWER ON/OFF or STOP-
RUN.