Siemens Simatic S7-200 System Manual page 144

Programmable controller
Hide thumbs Also See for Simatic S7-200:
Table of Contents

Advertisement

CPU Memory: Data Types and Addressing Modes
At power on, the CPU checks the RAM to verify that the super capacitor successfully
maintained the data stored in RAM memory. If the RAM was successfully maintained, the
retentive areas of RAM are left unchanged. As shown in Figure 7-16, the non-retentive areas
of V memory are restored from the corresponding permanent area of V memory in the
EEPROM.
RAM
User program
CPU configuration
V memory
M memory
Timer and Counter
current values
Figure 7-16
If the contents of the RAM were not maintained (such as after an extended power failure),
the CPU clears the RAM (including both the retentive and non-retentive ranges) and sets the
Retentive Data Lost memory bit (SM0.2) for the first scan following power on. As shown in
Figure 7-17, the data stored in the permanent EEPROM are then copied to the RAM.
User program
CPU configuration
Timer and Counter
current values
Figure 7-17
7-14
The corresponding areas of
permanent V memory are copied
to the non-retentive areas of
V memory in RAM.
All other non-retentive
areas of memory are
set to 0.
Restoring Program Data on Power On (Data Was Successfully Maintained in RAM)
RAM
V memory (permanent area)
V memory
M memory
M memory (permanent area),
if defined as retentive
All other areas of memory
are set to 0.
Restoring Program Data on Power On (Data Not Maintained in RAM)
EEPROM (Permanent)
User program
CPU configuration
V memory
(permanent area)
M memory
(permanent area)
EEPROM (Permanent)
User program
CPU configuration
V memory
(permanent area)
M memory
(permanent area)
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02

Advertisement

Table of Contents
loading

Table of Contents