NuMicro® NUC029LEE/NUC029SEE
32-bit Arm
®
Cortex
®
-M0 Microcontroller
Aug, 2018
Page
449
of
497
Rev 1.00
N
U
MICRO
®
N
UC02
9L
E
E
/N
UC029
S
E
E
T
E
CHN
ICA
L R
E
F
E
R
E
NC
E
M
A
NU
A
L
and data buffer status in each endpoint.
6.16.5.3 Digital Phase Lock Loop (DPLL)
The bit rate of USB data is 12 MHz. The DPLL uses the 48 MHz which comes from the clock
controller to lock the input data RXDP and RXDM. The 12 MHz bit rate clock is also converted
from DPLL.
6.16.5.4 Floating Detection De-bouncing
A USB device may be plugged-in or plugged-out from the USB host. To monitor the state of a
USB device when it is detached from the USB host, the device controller provides hardware de-
bouncing for USB floating detection interrupt to avoid bounce problems on USB plug-in or unplug.
Floating detection interrupt appears about 10 ms later than USB plug-in or plug-out. User can
acknowledge USB plug-in/plug-out by reading USB_FLDET register. The FLDET flag represents
the current state of USB_VBUS without de-bouncing. If the FLDET flag is 1, it means the USB
cable is plugged-in. If user polls the flag to check USB state, software de-bouncing must be
added if needed.
6.16.5.5 Interrupt
This USB provides 1 interrupt vector with 4 interrupt events (WAKE-UP, FLDET, USB and BUS).
The WAKE-UP event is used to wake-up the system clock when Power-down mode is enabled.
(The power mode function is defined in system Power-down control register, PWRCON). The
FLDET event is used for USB plug-in or unplug. The USB event notifies users of some USB
requests, such as IN ACK, OUT ACK., and the BUS event notifies users of some bus events,
such as suspend and, resume. The related bits must be set in the interrupt enable register
(USB_INTEN) of USB Device Controller to enable USB interrupts.
Wake-up interrupt is only present when the chip enters Power- down mode and then wake-up
event had happened. After the chip enters Power-down mode, any change on USB_VBUS,
USB_D+ and USB_D- can wake up this chip if the USB wake-up function is enabled. If this
change is not intentionally, no interrupt but wake-up interrupt will occur. After USB wake-up, this
interrupt will occur when no other USB interrupt events are presented for more than 20ms. The
following figure is the control flow of wake-up interrupt.