"Only store in load memory" attribute for the S7-1200/S7-1500

Instructions

Data blocks with the "Only store in load memory" attribute (unlinked DBs) are data blocks that do not occupy any space in the main memory of the controller and only use space in the load memory of the CPU. They are therefore suitable for storing large volumes of data that are not needed often in the controller's program.

Example

Since the main memory has only a limited size, for recipe management, for example, multiple data blocks with different recipe values can only be stored in the load memory. Then, in the main memory there is only a working DB that contains the current recipe. If the DBs mentioned above are configured and loaded into the CPU, then those data blocks are only available in the CPU's load memory and hence do not take up any space in the main memory.

Fig. 1 shows an example of data transfer between the unlinked DBs in the load memory and the sequence-relevant DB in the main memory. Use the two instructions below to program data transfer:

• READ_DBL: Read from the data block in the load memory.
• WRIT_DBL: Write to the data block in the load memory.