HC08KL8GRSSLASHD datasheet(115/256 Pages) NXP

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Universal Serial Bus Module (USB)

Overview

MC68HC08KL8 — Rev. 2.0

General Release Specification

Universal Serial Bus Module (USB)

9.3.3 Suspend

The MC68HC08KL8 supports suspend mode for low power. Suspend

mode should be entered when the USB data lines are in the idle state for

more than 3.0 ms. Entry into suspend mode is controlled by the

SUSPND bit in the USB interrupt register. Any low-speed bus activity

should keep the device out of the suspend state. Low-speed devices are

kept awake by periodic low-speed EOP signals from the host. This is

referred to as low speed keep alive (refer to Section 11.2.5.1 of the

Universal Serial Bus Specification Rev. 1.0).

Firmware should monitor the EOPF flag and enter suspend mode by

setting the SUSPND bit if an EOP is not detected for 3 ms.

Per the USB specification, the MC68HC08KL8 is required to draw less

than 500

µA from the V

DD supply when it is in the suspend state. This

includes the current supplied by the voltage regulator to the 15 k

Ω to

ground termination resistors placed at the host end of the USB bus. This

low-current requirement means that firmware is responsible for entering

stop mode once the USB module has been placed in the suspend state.

9.3.4 Resume After Suspend

The MC68HC08KL8 can be activated from the suspend state by normal

bus activity, a USB reset signal, or by a forced resume driven from the

MC68HC08KL8.

9.3.4.1 Host Initiated Resume

The host signals resume by initiating resume signalling (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.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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