BECKHOFF CX51x0 - Manual (Page 70)

Commissioning/Configuration
Boot Option #n (n={1..11})
Options: Service Stick / CFast/SSD / Hard Disk / CD/DVD / USB Stick /
USB Floppy / USB Hard Disk / USB / CD/DVD / Network / USB LAN / OSLoader
The boot option defined as #1 has the highest priority, followed by the second, third, etc. priority.
CX51x0 70 Version 1.0