Siemens LOGO! Series Manual page 204

LOGO! functions
4.4 Special functions list - SF
To set the start value, press
If the referenced block (B021, in the example) returns a value that lies out of the valid range,
the value is rounded to the next valid value.
The view in parameter assignment mode (example):
204
or to access the following screen form:
Manual, 04/2011, A5E03556174-01
LOGO!