英文マニュアル　A75M.pdf　を見ると下の箇所くらいしかない


Legacy USB Support
Use this option to select legacy support for USB devices. There are four
confi guration options: [Enabled], [Auto], [Disabled] and [UEFI Setup Only].
The default value is [Enabled]. Please refer to below descriptions for the
details of these four options:
[Enabled] - Enables support for legacy USB.
[Auto] - Enables legacy support if USB devices are connected.
[Disabled] - USB devices are not allowed to use under legacy OS and
UEFI setup when [Disabled] is selected. If you have USB compatibility is-
sue, it is recommended to select [Disabled] to enter OS.
[UEFI Setup Only] - USB devices are allowed to use only under UEFI
setup and Windows / Linux OS.