68HC705JB4 datasheet(75/134 Pages) FREESCALE

75 / 134 page

February 24, 1999

GENERAL RELEASE SPECIFICATION

MC68HC05JB4

UNIVERSAL SERIAL BUS MODULE

MOTOROLA

REV 2

10-9

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 MC68HC05JB4 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 MC68HC05JB4 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 MC68HC05JB4 can be activated from the suspend state by normal bus

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

MC68HC05JB4.

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.

10.2.4.2 USB Reset Signalling

Reset can wake a device from the suspended mode. A device may take up to 10

ms to wake up from the suspended state.

10.2.4.3 Remote Wake-up

The MC68HC05JB4 also supports the remote wake-up 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.

Freescale Semiconductor, Inc.

For More Information On This Product,

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68HC705JB4 Datasheet(PDF) 75 Page - Freescale Semiconductor, Inc

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