From 15812-TRE-070-3 ATST Enclosure Design Report:

AZIMUTH END STOP

The Azimuth End Stop provides a shock absorbing hard limit on both ends of the travel (+200º/-200º). As the overall travel is higher than one complete turn, the mechanism shall be equipped with a bistable mechanism to limit the rotation in the common part of the travel in one direction, allowing it in the other one.
For the sake of compactness and direct load transmission, the End Stop Mechanism is located in the same space as the bogies (as if it were another bogie) and moves laterally between two equilibrium positions to position a lever in the radius in which it can find the end stop plate. In this condition when the lever reaches the end stop plate the shock absorber is compressed.

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At the center of travel there is a redundant pair of cams that determine the lateral position of the mechanism on each part of the travel. The bi-stable mechanism will be equipped with a limit switch to inform the control system whether the mechanism is in the positive or negative azimuth travel.

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Animation of Enclosure Azimuth Topple Block End Stops

End Stop Mechanism

The above diagram (taken from 15812-DWG-M-5.2.1.4-000) show the relative locations of the two stop plates (inner and outer) as well as the two sliding plates (inner and outer). This allows for a nominal range of motion of 400°.