Siemens SIMATIC S7 System Manual page 142

PLC device configuration
6.1 Configuring the operation of the PLC system
By default, the CPU has no defined retentive memory areas, but you can configure the
retentive ranges:
● The S7-200 SMART CPU models CPU SR20, CPU ST20, CPU SR30, CPU ST30, CPU
SR40, CPU ST40, CPU SR60, and CPU ST60 have a maximum of 10 Kbytes of retentive
memory.
● The S7-200 SMART CPU models CPU CR20s, CPU CR30s, CPU CR40s, and CPU
CR60s have a maximum of 2 Kbytes of retentive memory.
Data retention after CPU power interruption
The CPU performs the following actions regarding retentive memory at power down and
power up:
● At power down:
The CPU saves the memory ranges designated as retentive to permanent memory.
● At power up:
The CPU first clears V, M, C, and T memory, copies any initial values from the data block
to V memory, and then copies the saved retentive values from permanent memory to
RAM.
S7-200 SMART CPU memory addresses for retentive ranges
Data type Desc.
V Data Memory
T Timers
C Counters
M Flag bits
142
CPU CR20s CPU SR20
CPU CR30s CPU ST20
CPU CR40s
CPU CR60s
VB0-VB8191 VB0-VB8191
T0-T31, T0-T31,
T64-T95 T64-T95
C0-C255 C0-C255
MB0-MB31 MB0-MB31
CPU SR30 CPU SR40
CPU ST30 CPU ST40
VB0-VB12281 VB0-VB16383
T0-T31, T0-T31,
T64-T95 T64-T95
C0-C255 C0-C255
MB0-MB31 MB0-MB31
System Manual, V2.3, 07/2017, A5E03822230-AF
CPU SR60
CPU ST60
VB0-VB20479
T0-T31,
T64-T95
C0-C255
MB0-MB31
S7-200 SMART