Access Speed Of Memory Areas - Siemens S7-1200 Programming Manualline

3 General Programming
3.4 Storage concept
3.4.4

Access speed of memory areas

STEP 7 offers different options of memory accesses. For system-related reasons
there are faster and slower accesses to different memory areas.
Figure 3-20: Different memory accesses
Access speed
Non-structured
elementary data type FC
parameter
Non-retain tags
Temporary tags
Indexed accesses with
runtime tindex
Accesses to checks for at
runtime require
(register, indirect and
indirect DB accesses)
Fastest accesses in the S7-1200/1500 in descending order
1. Optimized blocks: Temporary tags, parameters of an FC and FB, non-retentive
static tags
2. Optimized blocks whose accesses for compiling are known:
– Retentive FB tags
–
Optimized global DBs
3. Access to non-optimized blocks
4. Indexed accesses with index that was calculated at runtime (e.g. Motor [i])
5. Accesses that require checks at runtime
–
Accesses to DBs that are created at runtime or which were opened
indirectly (e.g. OPN DB[i])
–
Register access or indirect memory access
6. Copying of structures between optimized and non-optimized blocks (apart from
Array of Bytes)
Programming Guideline for S7-1200/1500
V1.2, Entry ID: 81318674
1
1
1
4
5
5
5
Copying between optimized
and non-optimized blocks
2
Access to optimized DBs
fast intermediate
Retentive tags
6
3
slow
2
Access to non-optimized
blocks
44