LM3S5R36_13 Datasheet, PDF (799/1063 Pages) Texas Instruments – LM3S5R36 Microcontroller

NRND: Not recommended for new designs.
Stellaris^® LM3S5R36 Microcontroller
Setting the Device Address
When a Host is attempting to enumerate the USB Device, it requests that the Device change its
address from zero to some other value. The address is changed by writing the value that the Host
requested to the USB Device Functional Address (USBFADDR) register. However, care should
be taken when writing to USBFADDR to avoid changing the address before the transaction is
complete. This register should only be set after the SET_ADDRESS command is complete. Like all
control transactions, the transaction is only complete after the Device has left the STATUS phase.
In the case of a SET_ADDRESS command, the transaction is completed by responding to the IN
request from the Host with a zero-byte packet. Once the Device has responded to the IN request,
the USBFADDR register should be programmed to the new value as soon as possible to avoid
missing any new commands sent to the new address.
Note:
If the USBFADDR register is set to the new value as soon as the Device receives the OUT
transaction with the SET_ADDRESS command in the packet, it changes the address during
the control transfer. In this case, the Device does not receive the IN request that allows the
USB transaction to exit the STATUS phase of the control transfer because it is sent to the
old address. As a result, the Host does not get a response to the IN request, and the Host
fails to enumerate the Device.
17.3.1.6
SUSPEND
When no activity has occurred on the USB bus for 3 ms, the USB controller automatically enters
SUSPEND mode. If the SUSPEND interrupt has been enabled in the USB Interrupt Enable (USBIE)
register, an interrupt is generated at this time. When in SUSPEND mode, the PHY also goes into
SUSPEND mode. When RESUME signaling is detected, the USB controller exits SUSPEND mode
and takes the PHY out of SUSPEND. If the RESUME interrupt is enabled, an interrupt is generated.
The USB controller can also be forced to exit SUSPEND mode by setting the RESUME bit in the USB
Power (USBPOWER) register. When this bit is set, the USB controller exits SUSPEND mode and
drives RESUME signaling onto the bus. The RESUME bit must be cleared after 10 ms (a maximum
of 15 ms) to end RESUME signaling.
To meet USB power requirements, the controller can be put into Deep Sleep mode which keeps
the controller in a static state. The USB controller is not able to Hibernate because all the internal
states are lost as a result.
17.3.1.7
Start-of-Frame
When the USB controller is operating in Device mode, it receives a Start-Of-Frame (SOF) packet
from the Host once every millisecond. When the SOF packet is received, the 11-bit frame number
contained in the packet is written into the USB Frame Value (USBFRAME) register, and an SOF
interrupt is also signaled and can be handled by the application. Once the USB controller has started
to receive SOF packets, it expects one every millisecond. If no SOF packet is received after 1.00358
ms, the packet is assumed to have been lost, and the USBFRAME register is not updated. The
USB controller continues and resynchronizes these pulses to the received SOF packets when these
packets are successfully received again.
17.3.1.8
USB RESET
When a RESET condition is detected on the USB bus, the USB controller automatically performs
the following actions:
■ Clears the USBFADDR register.
■ Clears the USB Endpoint Index (USBEPIDX) register.
October 06, 2012
799
Texas Instruments-Production Data