Siemens Simatic Box PC 840 V2 Getting Started page 19

Additional permissible PC mounting positions according to UL508/CSA 22.2 No. 142
An inclination of ±15° is allowed in this mounting position.
Position 5 (ports facing down)
CD/DVD and floppy drives may not be operated.
SIMATIC Box PC 840 V2
Getting Started, Edition 05/2006, A5E00244266-02
Application planning
3.5 Permitted mounting positions
3-5