Specifications

3 General Programming

3.4 Storage concept

Programming Guideline for S7-1200/1500

V1.2, Entry ID: 81318674

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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 fast intermediate slow

Temporary tags

Non-retain tags

Non-structured

elementary data type FC

parameter

Accesses to checks for at

runtime require

(register, indirect and

indirect DB accesses)

Access to non-optimized

blocks

Indexed accesses with

runtime tindex

Access to optimized DBs

Retentive tags

Copying between optimized

and non-optimized blocks

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)