USB on-the-go high-speed (OTG_HS) RM0090
1378/1731 DocID018909 Rev 11
35.6 USB functional description on host mode
This section gives the functional description of the OTG_HS in the USB host mode. The
OTG_HS works as a USB host in the following circumstances:
• OTG A-host
OTG A-device default state when the A-side of the USB cable is plugged in
• OTG B-host
OTG B-device after HNP switching to the host role
• A-device
If the ID line is present, functional and connected to the A-side of the USB cable, and
the HNP-capable bit is cleared in the Global USB Configuration register (HNPCAP bit
in OTG_HS_GUSBCFG). Integrated pull-down resistors are automatically set on the
DP/DM lines.
• Host only (Figure 389: USB host-only connection).
The force host mode bit in the global USB configuration register (FHMOD bit in
OTG_HS_GUSBCFG) forces the OTG_HS core to operate in USB host-only mode. In
this case, the ID line is ignored even if it is available on the USB connector. Integrated
pull-down resistors are automatically set on the OTG_HS_FS_DP/OTG_HS_FS_DM
lines.
Note: On-chip 5 V V
BUS
generation is not supported. As a result, a charge pump or a basic power
switch (if a 5 V supply is available on the application board) must be added externally to
drive the 5 V V
BUS
line. The external charge pump can be driven by any GPIO output. This
is required for the OTG A-host, A-device and host-only configurations.
The V
BUS
input ensures that valid V
BUS
levels are supplied by the charge pump during USB
operations while the charge pump overcurrent output can be input to any GPIO pin
configured to generate port interrupts. The overcurrent ISR must promptly disable the V
BUS
generation.
35.6.1 SRP-capable host
SRP support is available through the SRP capable bit in the global USB configuration
register (SRPCAP bit in OTG_HS_GUSBCFG). When the SRP feature is enabled, the host
can save power by switching off the V
BUS
power while the USB session is suspended. The
SRP host mode program model is described in detail in Section : A-device session request
protocol.
35.6.2 USB host states
Host port power
On-chip 5 V V
BUS
generation is not supported. As a result, a charge pump or a basic power
switch (if a 5 V supply voltage is available on the application board) must be added
externally to drive the 5 V V
BUS
line. The external charge pump can be driven by any GPIO
output. When the application powers on V
BUS
through the selected GPIO, it must also set
the port power bit in the host port control and status register (PPWR bit in OTG_HS_HPRT).
V
BUS
valid
When SRP or HNP is enabled the VBUS sensing pin (PB13) pin should be connected to
V
BUS
. The V
BUS
input ensures that valid V
BUS
levels are supplied by the charge pump
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