Best Possible Data Storage In The Processor On S7-1500 - Siemens S7-1200 Programming Manualline

2 S7-1200/1500 Innovations
2.6 Optimized blocks
Optimized blocks have a memory reserves for reloading in running operation
(see chapter 3.2.7 Downloading without reinitialization).
Only the symbolic access exists for optimized blocks.
2.6.3

Best possible data storage in the processor on S7-1500

For reasons of compatibility to the first SIMATIC controllers the "Big-Endian"
principle of data storage was adopted in the S7-300/400 controllers.
The new S7-1500 controller generation always accesses 4 byte (32 bit) in "Little-
Endian" sequence due to the changed processor architecture. This results in the
following system-specific properties.
Figure 2-8: Data access of a S7-1500 controller
Standard
0
0
1
B
2
0
y
3 1
t
2
4
e
3
s
5
X
6
7
8
0
9 1
Table 2-3: Data access of a S7-1500 controller
1. In the event of an unfavorable offset,
the controller needs 2x16 bit accesses
in order to be able to read a 4 byte
value (e.g. REAL value).
In addition the bytes have to be
changed.
2. The complete byte is read and masked
per bit access.
The complete byte is blocked for any
other access.
3. Maximum block size is 64kB.
Programming Guideline for S7-1200/1500
V1.2, Entry ID: 81318674
Standard block
max. 64kB
Bits
1 2 3 4 5 6 7
BYTE
Conversion for
processor access:
Big Little Endian
REAL
Big-Endian
1
X
2
WORD
Big-Endian
Standard block
Optimized block
max. 16MB
Bits
Optimized
0 1 2 3 4
Best possible processor
3
2
REAL
B
1
y
0 Little-Endian
t
1
e
WORD
s
0 Little-Endian
BYTE
X
X
2
Reserve
Optimized block
The controller stores the tags, access
optimized. An access is performed with
32 bit (REAL).
A changing of the bytes is not
necessary.
Each bit is assigned a byte.
When accessing, the controller does not
have to mask the byte.
Maximum block size can be up to
16MB.
5 6 7
data storage:
No conversion
required.
1
12