MC908JB12DWE Datasheet, PDF (174/332 Pages) Freescale Semiconductor, Inc – MC68HC908JB16 Technical Data

Universal Serial Bus Module (USB)
The reset flag bit (RSTF) in the USB interrupt register 1 (UIR1) also will
be set after the internal reset is removed. Refer to 11.8.3 USB Interrupt
Register 1 for more detail.
After a reset is removed, the device will be in the default, but not yet
addressed or configured state (refer to Section 9.1 USB Device States
of the Universal Serial Bus Specification Rev. 2.0). The device must be
able to accept a device address via a SET_ADDRESS command (refer
to Section 9.4 Standard Device Request in the Universal Serial Bus
Specification Rev. 2.0) no later than 10ms after the reset is removed.
Reset can wake a device from the suspended mode.
NOTE:
USB reset can be configured not to generate a reset signal to the CPU
by setting the URSTD bit of the configuration register (see Section 5.
Configuration Register (CONFIG)). When a USB reset is detected, the
CPU generates an USB interrupt.
11.5.3 Suspend
The MCU supports suspend mode for low power. Suspend mode should
be entered when the USB data lines are in the idle state for more than
3ms. 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 11.8.4.1 Low-speed Keep-alive in the
Universal Serial Bus Specification Rev. 2.0).
Firmware should monitor the EOPF flag and enter suspend mode by
setting the SUSPND bit if an EOP is not detected for 3ms.
Per the USB specification, the bus powered USB system is required to
draw less than 500µA from the V_DD supply when in the suspend state.
This includes the current supplied by the voltage regulator to the 1.5kΩ
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.
Technical Data
174
Universal Serial Bus Module (USB)
MC68HC908JB16 — Rev. 1.1
Freescale Semiconductor