最終更新:2018-06-15 (金) 11:00:45 (437d)  

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必要とするバスからの電流の1/2(mA)。

フィールドオフセットサイズ説明
bMaxPower81必要とするバスからの電流の1/2(mA)。最大 500(=0xFA*2)mA。値の1/2を設定するのは1byteに収めたかったため

メモ

  • 最大 500(=0xFA*2)mA。
  • 値の1/2を設定するのは 1 byte に丸めたかったがため。

USB 3.0

  • USB 3.0では消費電流量bMaxPowerの単位が2mAから8mAへ変更されている
    • Expressed in 2-mA units when the device is operating in high-speed mode and in 8-mA units when operating at Gen X speed.
    • (i.e., 50 = 100 mA when operating at high-speed and 50 = 400 mA when operating at Gen X speed).

メモ

  • Maximum power consumption of the USB device from the bus in this specific configuration when the device is fully operational.
  • Expressed in 2 mA units (i.e., 50 = 100 mA).
  • Note: A device configuration reports whether the configuration is bus-powered or selfpowered.
  • Device status reports whether the device is currently self-powered.
  • If a device is disconnected from its external power source, it updates device status to indicate that it is no longer self-powered.
  • A device may not increase its power draw from the bus, when it loses its external power source, beyond the amount reported by its configuration.
  • If a device can continue to operate when disconnected from its external power source, it continues to do so. If the device cannot continue to operate, it fails operations it can no longer support.
  • The USB System Software may determine the cause of the failure by checking the status and noting the loss of the device’s power source.