When assigning the slaves in the master system several data blocks are defined in the peripheral address space at the same time. The block-wise reloading of data is used to reach a higher security and a better detection of short-term failures.

To reload the data from or to the periphery the use of SFC14 and SFC15 is recommended. When exchanging data with an

S7-300 more than one call of SFC14/SFC15 is required because the data block length is limited to 32 bytes. When working with the S7-400 family, 122 bytes are available per data block. This is the reason why you find different GSD files on the data medium.