M68HC08 datasheet(175/332 Pages) FREESCALE

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Universal Serial Bus Module (USB)

MC68HC908JB16 — Rev. 1.1

Technical Data

Freescale Semiconductor

Universal Serial Bus Module (USB)

175

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.

M68HC08 Datasheet(PDF) 175 Page - Freescale Semiconductor, Inc