There are some very good reference books written by Hans Berger, commonly known as "Berger books". There's one for each of the families of S5. If I remember correctly, the book for the 100U series is a primer with plenty of examples.
Regards,
Rob
Dazmac:
Check out the optional Step7-MicroWin command library. It has both the USS and Modbus protocol blocks and instructions for their use.
Regards,
Rob
Ray:
SFC20 (BLKMOV)is in the standard library of Step7. You can either open the library in Simatic Manager, or you can access it from within the ladder editor under Libraries->Standard Library->System Function Blocks
Regards,
Rob