Recovery From A Lost Password; Data Storage, Memory Areas And Addressing - Siemens SIMATIC S7 System Manual

3.1.5

Recovery from a lost password

If you have lost the password for a password-protected CPU, use an empty transfer card to
delete the password-protected program. The empty transfer card erases the internal load
memory of the CPU. You can then download a new user program from STEP 7 Basic to the
CPU.
For information about the creation and use of an empty transfer card, see the section of
transfer cards (Page 63).
If you insert a transfer card in a running CPU, the CPU goes to STOP. Control devices can
fail in an unsafe condition, resulting in unexpected operation of controlled equipment. Such
unexpected operations could result in death or serious injury to personnel, and/or damage
to equipment.
You must remove the transfer card before setting the CPU to RUN mode.
3.2

Data storage, memory areas and addressing

The CPU provides several options for storing data during the execution of the user program:
● Global memory: The CPU provides a variety of specialized memory areas, including
● Data block (DB): You can include DBs in your user program to store data for the code
● Temp memory: Whenever a code block is called, the operating system of the CPU
Each different memory location has a unique address. Your user program uses these
addresses to access the information in the memory location.
Memory area
I
Process image input
I_:P
(Physical input)
Q
Process image output
Q_:P
(Physical output)
M
Bit memory
S7-1200 Programmable controller
System Manual, 11/2009, A5E02486680-02
WARNING
inputs (I), outputs (Q) and bit memory (M). This memory is accessible by all code blocks
without restriction
blocks. The data stored persists when the execution of the associated code block comes
to an end. A "global" DB stores data that can be used by all code blocks, while an
instance DB stores data for a specific FB and is structured by the parameters for the FB.
allocates the temporary, or local, memory (L) to be used during the execution of the
block. When the execution of the code block finishes, the CPU reallocates the local
memory for the execution of other code blocks.
3.2 Data storage, memory areas and addressing
Description
Copied from physical inputs at the beginning
of the scan cycle
Immediate read of the physical input points
on the CPU, SB, and SM
Copied to physical outputs at the beginning
of the scan cycle
Immediate write to the physical output points
on the CPU, SB, and SM
Control and data memory
PLC concepts
Force Retentive
No No
Yes No
No No
Yes No
No Yes
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