mc68hc05jb4p Freescale Semiconductor, Inc, mc68hc05jb4p Datasheet - Page 75

• Manufacturer Part Number: mc68hc05jb4p
• Description: Mc68hc705jb4 Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

10.2.3 Suspend
10.2.4 Resume After Suspend
10.2.4.1 Host Initiated Resume
10.2.4.2 USB Reset Signalling
10.2.4.3 Remote Wake-up
MC68HC05JB4
REV 2
Reset can wake a device from the suspended mode. A device may take up to
10ms to wake up from the suspended state.
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 A from the V
supplied by the voltage regulator to the 15 K
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.
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.
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.
Reset can wake a device from the suspended mode. A device may take up to 10
ms to wake up from the suspended state.
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.
DD
For More Information On This Product,
supply when in the suspend state. This includes the current
UNIVERSAL SERIAL BUS MODULE
Go to: www.freescale.com
February 24, 1999
GENERAL RELEASE SPECIFICATION
to ground termination resistors