LM3S9B81 Datasheet, PDF (866/1155 Pages) Texas Instruments – Stellaris® LM3S9B81 Microcontroller

Universal Serial Bus (USB) Controller
Table 20-2. Signals for USB (108BGA) (continued)
Pin Name
Pin Number Pin Mux / Pin Pin Type Buffer Type^a Description
Assignment
USB0RBIAS
B12
fixed
O
Analog 9.1-kΩ resistor (1% precision) used internally for
USB analog circuitry.
USB0VBUS
D12
PB1
I/O
Analog This signal is used during the session request
protocol. This signal allows the USB PHY to both
sense the voltage level of VBUS, and pull up VBUS
momentarily during VBUS pulsing.
a. The TTL designation indicates the pin has TTL-compatible voltage levels.
20.3
Functional Description
Note:
A 9.1-kΩ resistor should be connected between the USB0RBIAS and ground. The 9.1-kΩ
resistor should have a 1% tolerance and should be located in close proximity to the
USB0RBIAS pin. Power dissipation in the resistor is low, so a chip resistor of any geometry
may be used.
The Stellaris^® USB controller provides full OTG negotiation by supporting both the session request
protocol (SRP) and the host negotiation protocol (HNP). The session request protocol allows devices
on the B side of a cable to request the A side device turn on VBUS. The host negotiation protocol
is used after the initial session request protocol has powered the bus and provides a method to
determine which end of the cable will act as the Host controller. When the device is connected to
non-OTG peripherals or devices, the controller can detect which cable end was used and provides
a register to indicate if the controller should act as the Host or the Device controller. This indication
and the mode of operation are handled automatically by the USB controller. This auto-detection
allows the system to use a single A/B connector instead of having both A and B connectors in the
system and supports full OTG negotiations with other OTG devices.
In addition, the USB controller provides support for connecting to non-OTG peripherals or Host
controllers. The USB controller can be configured to act as either a dedicated Host or Device, in
which case, the USB0VBUS and USB0ID signals can be used as GPIOs. However, when the USB
controller is acting as a self-powered Device, a GPIO input or analog comparator input must be
connected to VBUS and configured to generate an interrupt when the VBUS level drops. This
interrupt is used to disable the pullup resistor on the USB0DP signal.
Note: When USB is used in the system, the minimum system frequency is 20 MHz.
20.3.1
Operation as a Device
This section describes the Stellaris^® USB controller's actions when it is being used as a USB Device.
Before the USB controller's operating mode is changed from Device to Host or Host to Device,
software must reset the USB controller by setting the USB0 bit in the Software Reset Control 2
(SRCR2) register (see page 197). IN endpoints, OUT endpoints, entry into and exit from SUSPEND
mode, and recognition of Start of Frame (SOF) are all described.
When in Device mode, IN transactions are controlled by an endpoint’s transmit interface and use
the transmit endpoint registers for the given endpoint. OUT transactions are handled with an
endpoint's receive interface and use the receive endpoint registers for the given endpoint.
When configuring the size of the FIFOs for endpoints, take into account the maximum packet size
for an endpoint.
■ Bulk. Bulk endpoints should be the size of the maximum packet (up to 64 bytes) or twice the
maximum packet size if double buffering is used (described further in the following section).
866
June 29, 2010
Texas Instruments-Advance Information