MC908JB12DWE Datasheet, PDF (175/332 Pages) Freescale Semiconductor, Inc – MC68HC908JB16 Technical Data

Universal Serial Bus Module (USB)
11.5.4 Resume After Suspend
The MCU can be activated from the suspend state by normal bus
activity, a USB reset signal, or by a forced resume driven from the MCU.
11.5.4.1 Host Initiated Resume
The host signals resume by initiating resume signalling (K state) for at
least 20ms followed by a standard low-speed EOP signal. This 20ms
ensures that all devices in the USB network are awakened.
After resuming the bus, the host must begin sending bus traffic within
3ms to prevent the device from re-entering suspend mode.
11.5.4.2 USB Reset Signalling
Reset can wake a device from the suspended mode.
11.5.4.3 Remote Wakeup
The MCU also supports the remote wakeup feature. The firmware has
the ability to exit suspend mode by signaling a resume state to the
upstream host or hub. A non-idle state (K state) on the USB data lines is
accomplished by asserting the FRESUM bit in the UCR1 register.
When using the remote wakeup capability, the firmware must wait for at
least 5ms after the bus is in the idle state before sending the remote
wakeup resume signaling. This allows the upstream devices to get into
their suspend state and prepare for propagating resume signaling. The
FRESUM bit should be asserted to cause the resume state on the USB
data lines for at least 10ms, but not more than 15ms. Note that the
resume signalling is controlled by the FRESUM bit and meeting the
timing specifications is dependent on the firmware. When FRESUM is
cleared by firmware, the data lines will return to their high-impedance
state.
Refer to register definitions (see 11.8.6 USB Control Register 1) for
more information about how the force resume (FRESUM) bit can be
used to initiate the remote wakeup feature.
MC68HC908JB16 — Rev. 1.1
Freescale Semiconductor
Universal Serial Bus Module (USB)
Technical Data
175