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Universal Serial Bus, OTG Capable Controller
MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
15-40 Freescale Semiconductor
15.7.4 USB Suspend State
USB bus powered devices are required to respond to a 3ms lack of activity on the USB bus by going into
a suspend state. Software is notified of the suspend condition via the transition in the port status and control
register or, optionally, an interrupt can be generated which is controlled by the interrupt enable register. In
the suspend state, a USB device has a maximum USB bus power budget of 500uA. To achieve that level
of power conservation, most of the device circuits need to be switched off. When the clock is disabled to
the USB-FScore all functions are disabled, but all operational states are retained The transceiver VP and
VM signals can be used to construct a circuit that is able to detect the resume signaling on the bus and
restore the clocks to the rest of the circuit when the USB host takes the bus out of the suspend state.