Universal Serial Bus InterfaceMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 24-131After a Port Change Detect, the device has reached the default state and the DCD can read the PORTSCnto determine if the device is operating in FS or HS mode. At this time, the device controller has reachednormal operating mode and DCD can begin enumeration according to the USB 2.0 Specification,Chapter 9, Device Framework.NOTEThe device DCD may use the FS/HS mode information to determine thebandwidth mode of the device.In some applications, it may not be possible to enable one or more pipes while in FS mode. Beyond thedata rate issue, there is no difference in DCD operation between FS and HS modes.24.11.2.2 Suspend/Resume24.11.2.2.1 Suspend DescriptionIn order to conserve power, USB_DR automatically enters the suspended state when no bus traffic hasbeen observed for a specified period. When suspended, the USB_DR maintains any internal status,including its address and configuration. Attached devices must be prepared to suspend at any time they arepowered, regardless of if they have been assigned a non-default address, are configured, or neither. Busactivity may cease due to the host entering a suspend mode of its own. In addition, a USB device shall alsoenter the suspended state when the hub port it is attached to is disabled.The USB_DR exits suspend mode when there is bus activity. It may also request the host to exit suspendmode or selective suspend by using electrical signaling to indicate remote wake-up. The ability of a deviceto signal remote wake-up is optional. The USB_DR is capable of remote wake-up signaling. When theUSB_DR is reset, remote wake-up signaling must be disabled.24.11.2.2.2 Suspend Operational ModelThe USB OTG moves into the suspend state when suspend signaling is detected or activity is missing onthe upstream port for more than a specific period. After the device controller enters the suspend state, theDCD is notified by an interrupt (assuming DC Suspend Interrupt is enabled). When the DCSuspend bit inthe PORTSCn is set to a '1', the device controller is suspended.DCD response when the device controller is suspended is application specific and may involve switchingto low power operation.Information on the bus power limits in suspend state can be found in USB 2.0 specification.24.11.2.2.3 ResumeIf the USB_DR is suspended, its operation is resumed when any non-idle signaling is received on itsupstream facing port. In addition, the USB_DR can signal the system to resume operation by forcingresume signaling to the upstream port. Resume signaling is sent upstream by writing a '1' to the Resumebit in the in the PORTSCn while the device is in suspend state. Sending resume signal to an upstream portshould cause the host to issue resume signaling and bring the suspended bus segment (one more devices)back to the active condition.
