HCS08 datasheet(321/374 Pages) NXP

321 / 374 page

Universal Serial Bus Device Controller (S08USBV1)

MC9S08JM60 Series Data Sheet, Rev. 5

Freescale Semiconductor

321

17.4.6

Suspend/Resume

The USB supports a single low-power mode called suspend. Getting into and out of the suspend state is

described in the following sections.

17.4.6.1

Suspend

The USB host can put a single device or the entire bus into the suspend state at any time. The MCU

supports suspend mode for low power. Suspend mode will be entered when the USB data lines are in the

idle state for more than 3 ms. Entry into suspend mode is announced by the SLEEPF bit in the INTSTAT

Per the USB specification, a low-power bus-powered USB device is required to draw less than 500 µA in

suspend state. A high-power device that supports remote wakeup and has its remote wake-up feature

enabled by the host can draw up to 2.5 mA of current. After the initial 3-ms idle, the USB device will reach

this state within 7 ms. This low-current requirement means that firmware is responsible for entering stop3

mode once the SLEEPF flag has been set and before the USB module has been placed in the suspend state.

On receipt of resume signaling from the USB, the module can generate an asynchronous interrupt to the

MCU which brings the device out of stop mode and wakes up the clocks. Setting the USBRESMEN bit in

the USBCTL0 register immediately after the SLEEPF bit is set enables this asynchronous notification

feature. The USB resume signaling will then cause the LPRESF bit to be set, indicating a low-power

SUSPEND resume, which will wake the CPU from stop3 mode.

During normal operation, while the host is sending SOF packets, the USB module will not enter suspend

mode.

17.4.6.2

Resume

There are three ways to get out of the suspend state. When the USB module is in suspend state, the resume

detection is active even if all the clocks are disabled and the MCU is in stop3 mode. The MCU can be

activated from the suspend state by normal bus activity, a USB reset signal, or upstream resume (remote

wakeup).

17.4.6.2.1

Host Initiated Resume

The host signals a resume from suspend by initiating resume signaling (K state) for at least 20 ms followed

by a standard low-speed EOP signal. This 20 ms ensures that all devices in the USB network are awakened.

After resuming the bus, the host must begin sending bus traffic within 3 ms to prevent the device from

re-entering suspend mode.

Depending on the power mode the device is in while suspended, the notification for a host initiated resume

will be different:

•

Run mode - RESUME must be set after SLEEPF becomes set to enable the RESUMEF interrupt.

Then, upon resume signaling, the RESUMEF interrupt will trigger after a K-state has been

observed on the USBDP/USBDN lines for 2.5 µs.

•

Stop3 mode - USBRESMEN must be set after SLEEPF becomes set to arm the LPRESF bit. Then,

upon a K-state on the bus while the device is in stop3 mode, the LPRESF bit will be set, indicating

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