Siemens SIMATIC FM 353 Manual page 261

Rotary axis
With rotary axes, the actual value is reset to "0" after one revolution. Rotary axes
thus have an infinite traversing range.
Fig. 9-4
Before you start a movement in "MDI" and "Automatic" modes, you can define a
fixed direction of rotation with R+ or R−.
Rotary axis end
Machine data item MD9 defines the value by which the FM 353 recognizes the end
of the rotary axis.
This value is the theoretical maximum that the actual value can reach. At this
value, display of the actual value switches back to 0.
The theoretical maximum, however, is never displayed, because it is physically
located in the same position as the start of the rotary axis (i.e. 0).
Example:
The following example in Figure 9-4 illustrates the behavior of the axis.
Assume you specify a value of 10,000 for the end of the rotary axis.
The value 10,000 will never be displayed. The display always rolls over from 9,999
to 0.
If the direction of rotation is negative, the display rolls over from 0 to 9,999.
FM 353 Stepper Drive Positioning Module
6ES7 353-1AH01-8BG0
0
9 999
5 000
Rotary axis
Description of Functions
9-61