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USB OTG Controller
HMC_MODE must be set to a value that routes the USB device controller to
USB pin group 1 (see Table 73). OTG_SYSCON_1.USB1_TRX_MODE must
be set to 3 to allow proper unidirectional operation of the 6-wire USB
transceiver.
A USB OTG transceiver can be used to provide USB device-only functionality
2
instead of a USB transceiver, with appropriate I
C and interrupt connectivity.
In this case, OTG_SYSCON_2.OTG_PADEN must be 0 and software passes
VBUS validity information from the USB OTG transceiver to the device
2
controller (USB_OTG) by reading VBUS status via the I
C link and updating
the value sent to the device controller via OTG_CTRL.BSESSVLD. In this
case, the OTG transceiver ID pin is left unconnected, and OTG functionality
is not available. Because the OTG transceiver provides integrated D+ pullup
capability, suspend mode control, and D+/D- pulldown controls, the hardware
features shown can be removed when an OTG transceiver is used. System
2
software must control those features via the OTG transceiver I
C register set.
When OTG_SYSCON_2.OTG_PADEN is 1, the status of GPIO0/USB.VBUS
is automatically provided to the USB device controller via hardware
mechanisms (when HMC_MODE provides USB device functionality to a USB
pin group). When OTG_SYSCON_2.OTG_PADEN is 0, the USB device
controller only sees the VBUS status from the software-controlled register
OTG_CTRL.BSESSVLD bit. In this case, software must monitor the
VBUS_DETECT signal (using GPIO0 if wired as shown), and update
OTG_CTRL.BSESSVLD whenever the VBUS_DETECT signal changes.
SPRU761A
Universal Serial Bus (USB)
295
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