ST STM32L4 5 Series Reference Manual page 1628

USB on-the-go full-speed (OTG_FS)
47.5.3 SRP dual role device
The SRP capable bit in the global USB configuration register (SRPCAP bit in
OTG_GUSBCFG) enables the OTG_FS core to switch off the generation of V
device to save power. Note that the A-device is always in charge of driving V
of the host or peripheral role of the OTG_FS.
The SRP A/B-device program model is described in detail in
programming
47.6 USB peripheral
This section gives the functional description of the OTG_FS in the USB peripheral mode.
The OTG_FS works as an USB peripheral in the following circumstances:
•
OTG B-Peripheral
–
•
OTG A-Peripheral
–
•
B-device
–
•
Peripheral only (see
–
Note: To build a bus-powered device implementation in case of the B-device or peripheral-only
configuration, an external regulator has to be added, that generates the V
from V
BUS
1628/1830
model.
OTG B-device default state if B-side of USB cable is plugged in
OTG A-device state after the HNP switches the OTG_FS to its peripheral role
If the ID line is present, functional and connected to the B-side of the USB cable,
and the HNP-capable bit in the Global USB Configuration register (HNPCAP bit in
OTG_GUSBCFG) is cleared.
Figure 519: USB_FS peripheral-only
The force device mode bit (FDMOD) in the
configuration register (OTG_GUSBCFG)
work as an USB peripheral-only. In this case, the ID line is ignored even if it is
present on the USB connector.
.
DocID024597 Rev 5
Section 47.16: OTG_FS
connection)
Section 47.15.4: OTG USB
is set to 1, forcing the OTG_FS core to
RM0351
for the A-
BUS
regardless
BUS
chip-supply
DD