Local Memory - Siemens S7-1200 Programming Manualline

3 General Programming
3.4 Storage concept
Advantages
User programs can be used universally and independent from the hardware.
The user program can be structured modularly without dividing bit memory
address areas for different users.
Optimized global DBs are clearly more powerful than the bit memory address
area that is not optimized for reasons of compatibility.
Recommendation
Do not use any bit memory and use global DBs instead.
Avoid hardware-dependent memory, such as, for example, clock memory or
counter. Use the IEC counter and timer in connection with multi-instances
instead (see chapter 3.2.5 Multi-instances). The IEC timers can be found under
"Instructions – Basic Instructions – Timer operations".
Figure 3-19: IEC Timers
3.4.3

Local memory

Static tags
Temporary tags
Recommendation
Use the static tags for values that are required for the next cycle.
Use the temporary tags as cache memory in current cycle. The access time for
temporary tags is shorter than for static ones.
Note
Optimized blocks: Temporary tags are initialized in any block call with the
"default value" (S7-1500 und S7-1200 Firmware V4).
Non-optimized blocks: Temporary tags are undefined for each call of the block.
Programming Guideline for S7-1200/1500
V1.2, Entry ID: 81318674
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