Datasheet

437
6120F–ATARM–03-Oct-06
AT91SAM7X512/256/128 Preliminary
34.3 Product Dependencies
For further details on the USB Device hardware implementation, see the specific Product Prop-
erties document.
The USB physical transceiver is integrated into the product. The bidirectional differential signals
DP and DM are available from the product boundary.
Two I/O lines may be used by the application:
• One to check that VBUS is still available from the host. Self-powered devices may use this
entry to be notified that the host has been powered off. In this case, the board pullup on DP
must be disabled in order to prevent feeding current to the host.
• One to control the board pullup on DP. Thus, when the device is ready to communicate with
the host, it activates its DP pullup through this control line.
34.3.1 I/O Lines
DP and DM are not controlled by any PIO controllers. The embedded USB physical transceiver
is controlled by the USB device peripheral.
To reserve an I/O line to check VBUS, the programmer must first program the PIO controller to
assign this I/O in input PIO mode.
To reserve an I/O line to control the board pullup, the programmer must first program the PIO
controller to assign this I/O in output PIO mode.
34.3.2 Power Management
The USB device peripheral requires a 48 MHz clock. This clock must be generated by a PLL
with an accuracy of ± 0.25%.
Thus, the USB device receives two clocks from the Power Management Controller (PMC): the
master clock, MCK, used to drive the peripheral user interface, and the UDPCK, used to inter-
face with the bus USB signals (recovered 12 MHz domain).
WARNING: The UDP peripheral clock in the Power Management Controller (PMC) must be
enabled before any read/write operations to the UDP registers including the UDP_TXCV
register.
34.3.3 Interrupt
The USB device interface has an interrupt line connected to the Advanced Interrupt Controller
(AIC).
Handling the USB device interrupt requires programming the AIC before configuring the UDP.