SAM7S256_14 Datasheet, PDF (503/775 Pages) ATMEL Corporation – ARM-based Flash MCU

35.3 Product Dependencies
For further details on the USB Device hardware implementation, see the specific Product Properties 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.
35.3.1 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.
35.3.2 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 interface 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.
35.3.3 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.
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
503