User Manual
Page 68
... keyboard legacy support for non-USB aware OSes. *Enable this option if you encounter USB compatibility issues it is a workaround for USB 2.0 devices. 4.6.6 USB Configuration H270M-ITX/ac Legacy USB Support Enable or disable Legacy OS Support for OSes without XHCI hand-off support. Select UEFI Setup Only to disable legacy USB support...
... keyboard legacy support for non-USB aware OSes. *Enable this option if you encounter USB compatibility issues it is a workaround for USB 2.0 devices. 4.6.6 USB Configuration H270M-ITX/ac Legacy USB Support Enable or disable Legacy OS Support for OSes without XHCI hand-off support. Select UEFI Setup Only to disable legacy USB support...