Fujitsu F2MC-16LX Hardware Manual page 314

CHAPTER 13 USB FUNCTION
Connection detection
The device sends a notification to the host PC.
The host monitors two signal lines (D + and D-) of the USB bus and recognizes that the device is connected
to it by discovering that either signal gets to "H" level.
A device must perform processing in the following steps:
1. Performs initialization (initializing everything including USB Function registers)
2. Discovers that a USB cable is connected to it by a level change of VBUS and confirms that VON is 1.
(If interrupt is enabled, a CPU interrupt is raised.)
3. Deselect RST in the UDCC register and enables HCON, and connects to the pull-up resistor of D+.
(When the pull-up resistor is not controlled, the HCON is valid before the RST is deselected.)
Host PC
USB bus reset
A bus reset is applied from the host PC to the device and the USB device core is initialized.
A device must perform processing in the following steps: (The first bus reset after USB has been connected
Initializes the USB Function with RST in the UDCC register.
1. The USB Function is initialized by the UDCC register.
2. Transmission/reception buffers in use and related control registers is re-set.
3. Firmware control is returned to pre-enumeration state.
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Figure 13.4-2 Example of Connecting USB Cable Terminal
VBUS(5V)
(3.3V)
D+
D-
does not need any processing.)
Device LSI
VON
VOFF
HCON