HC705JB2GRSSLASHH datasheet(77/128 Pages) NXP

77 / 128 page

August 28, 1998

GENERAL RELEASE SPECIFICATION

UNIVERSAL SERIAL BUS MODULE

REV 1.1

10-9

After a reset is removed, the device will be in the attached, but not yet addressed

or conﬁgured state (refer to Section 9.1 of the USB speciﬁcation). The device must

be able to accept a device address via a SET_ADDRESS command (refer to

section 9.4 of the USB speciﬁcation) no later than 10 ms after the reset is

removed.

Reset can wake a device from the suspended mode. A device may take up to

10ms to wake up from the suspended state.

10.2.3 Suspend

The MC68HC705JB2 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 USB speciﬁcation).

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 MC68HC705JB2 is required to draw less than

500

µA from the V

DD supply when 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.

10.2.4 Resume After Suspend

The MC68HC705JB2 can be activated from the suspend state by normal bus

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

MC68HC705JB2.

10.2.4.1 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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