MC9S08JM16 Datasheet, PDF (324/386 Pages) Freescale Semiconductor, Inc – Microcontrollers

Universal Serial Bus Device Controller (S08USBV1)
indicating a resume from low-power suspend. This will trigger an asynchronous interrupt to wake
the CPU from stop3 mode and resume clocks to the USB module.
NOTE
As a precaution, after LPRESF is set, firmware must check the state of the
USB bus to see if the K-state was a result of a transient event and not a true
host-initiated resume. If this is the case, then the device can drop back into
stop3 if necessary. To do this, the RESUME interrupt can be enabled in
conjunction with the USBRESMEN feature. Then, after LPRESF is set, and
a K-state is still detected approximately 2.5 µs after clocks have restarted,
firmware can check that the RESUMEF interrupt has triggered, indicating
resume signaling from the host.
17.4.6.2.2 USB Reset Signaling
Reset can wake a device from the suspend state.
17.4.6.2.3 Remote Wakeup
The USB device can send a resume event to the host by writing to the CRESUME bit. Firmware must first
set the bit for the time period required by the USB Specification Rev. 2.0 (Section 7.1.7.7) and then clear
it to 0.
17.4.7 Resets
The module supports multiple types of resets. The first is a bus reset generated by the USB Host, the
second is a module reset generated by the MCU.
17.4.7.1 USB Bus Reset
At any time, the USB host may issue a reset to one or all of the devices attached to the bus. A USB reset
is defined as a period of single ended zero (SE0) on the cable for greater than 2.5 μs. When the device
detects reset signaling, it resets itself to the unconfigured state, and sets its USB address zero. The USB
host uses reset signaling to force one or all connected devices into a known state prior to commencing
enumeration.
The USB module responds to reset signaling by asserting the USBRST interrupt in the INTSTAT register.
Software is required to service this interrupt to ensure correct operation of the USB.
17.4.7.2 USB Module Reset
USB module resets are initiated on-chip. During a module reset, the USB module is configured in the
default mode. The USB module can also be forced into its reset state by setting the USBRESET bit in the
USBCTL0 register. The default mode includes the following settings:
• Interrupts masked.
• USB clock enabled
• USB voltage regulator disabled
MC9S08JM16 Series Data Sheet, Rev. 2
324
Freescale Semiconductor