GD32W51x User Manual
823
Figure 24-2. Connection with host or device mode
VBUS
DM
DP
DP
DM
VBUS
5V Power
Supply
(needed in
host mode)
VDD
U
S
B
A
/B
co
n
n
e
ct
o
r
GPIO
USBFS
GND
When USBFS works in host mode (FHM bit is set and FDM bit is cleared), the VBUS is 5V
power detecting pin used for voltage detection defined in USB protocol. The internal PHY
cannot supply 5V VBUS power and only has some voltage comparers, charge and dis -charge
circuits on VBUS line. So if application needs VBUS power, an external power supply IC is
needed. The VBUS connection between USBFS and the USB connector can be omitted in
host mode, so USBFS doesn’t detect the voltage level on VBUS pin and always assumes that
the 5V power is present.
When USBFS works in device mode (FHM bit is cleared and FDM bit is set), the VBUS
detection circuit is connected to a GPIO pin. USBFS continuously monitor the VBUS voltage
by the GPIO pin and will immediately switch on the pull-up resistor on DP line once that the
VBUS voltage rise above the needed valid value. This will cause a connection. If the VBUS
voltage falls below the needed valid value, the pull-up resistor on DP line will be switched off
and a disconnection will happen.
The OTG mode connection is described in the
Figure 24-3. Connection with OTG mode
When USBFS works in OTG mode, the FHM, FDM bits in USBFS_GUSBCS and VBUSIG bit
in USBFS_GCCFG should be cleared. In this mode, the USBFS needs all the four pins: DM,
DP, VBUS and ID, and needs to use several voltage comparers to monitor the voltage on
these pins. USBFS also contains VBUS charge and discharge circuits to perform SRP request
described in OTG protocol. The OTG A-device or B-device is decided by the level of ID pins.
USBFS controls the pull-up or pull-down resistor during performing the HNP protocol.