LM3S3749 Datasheet, PDF (635/898 Pages) Texas Instruments – Stellaris® LM3S3749 Microcontroller

Stellaris® LM3S3749 Microcontroller
and the USB0DP/USB0DM lines of the USB bus are enabled. At the same time, the USB controller
is placed into a state, in which it does not respond to any USB signaling except a USB RESET.
When the SOFTCONN bit is cleared, the PHY is put into non-driving mode, USB0DP and USB0DM are
tristated, and the USB controller appears to other devices on the USB bus as if it has been
disconnected. The non-driving mode is the default so the USB controller appears disconnected until
the SOFTCONN bit has been set. The application software can then choose when to set the PHY
into its normal mode. Systems with a lengthy initialization procedure may use this to ensure that
initialization is complete, and the system is ready to perform enumeration before connecting to the
USB bus. Once the SOFTCONN bit has been set, the USB controller can be disconnected by clearing
this bit.
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: The USB controller does not generate an interrupt when the Device is connected to the
Host. However, an interrupt is generated when the Host terminates a session.
16.3.2
Operation as a Host
When the Stellaris USB controller is operating in Host mode, it can either be used for point-to-point
communications with another USB device or, when attached to a hub, for communication with
multiple devices. Before the USB controller's operating mode is changed from Host to Device or
Device to Host, software must reset the USB controller by setting the USB0 bit in the Software
Reset Control 2 (SRCR2) register (see page 248). Full-speed and low-speed USB devices are
supported, both for point-to-point communication and for operation through a hub. The USB controller
automatically carries out the necessary transaction translation needed to allow a low-speed or
full-speed device to be used with a USB 2.0 hub. Control, bulk, isochronous, and interrupt transactions
are supported. This section describes the USB controller's actions when it is being used as a USB
Host. Configuration of IN endpoints, OUT endpoints, entry into and exit from SUSPEND mode, and
RESET are all described.
When in Host mode, IN transactions are controlled by an endpoint’s receive interface. All IN
transactions use the receive endpoint registers and all OUT endpoints use the transmit endpoint
registers for a given endpoint. As in Device mode, the FIFOs for endpoints should 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).
■ Interrupt. Interrupt endpoints should be the size of the maximum packet (up to 64 bytes) or twice
the maximum packet size if double buffering is used.
■ Isochronous. Isochronous endpoints are more flexible and can be up to 1023 bytes.
■ Control. It is also possible to specify a separate control endpoint to communicate with a Device.
However, in most cases the USB controller should use the dedicated control endpoint to
communicate with a Device’s endpoint 0.
16.3.2.1
Endpoints
The endpoint registers are used to control the USB endpoint interfaces which communicate with
Device(s) that are connected. The endpoints consist of a dedicated control IN endpoint, a dedicated
control OUT endpoint, three configurable OUT endpoints, and three configurable IN endpoints.
November 17, 2011
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