AT91SAM7S128C-AU-999 Datasheet, PDF (516/775 Pages) ATMEL Corporation – ARM-based Flash MCU

35.5.3.2 Entering Attached State
When no device is connected, the USB DP and DM signals are tied to GND by 15 KΩ pull-down resistors inte-
grated in the hub downstream ports. When a device is attached to a hub downstream port, the device connects a
1.5 KΩ pull-up resistor on DP. The USB bus line goes into IDLE state, DP is pulled up by the device 1.5 KΩ resistor
to 3.3V and DM is pulled down by the 15 KΩ resistor of the host.
Warning: To write to the UDP_TXVC register, MCK clock must be enabled on the UDP. This is done in the Power
Management Controller.
After pullup connection, the device enters the powered state. In this state, the UDPCK and MCK must be enabled
in the Power Management Controller. The transceiver can remain disabled.
35.5.3.3 From Powered State to Default State
After its connection to a USB host, the USB device waits for an end-of-bus reset. The unmaskable flag END-
BUSRES is set in the register UDP_ISR and an interrupt is triggered.
Once the ENDBUSRES interrupt has been triggered, the device enters Default State. In this state, the UDP soft-
ware must:
• Enable the default endpoint, setting the EPEDS flag in the UDP_CSR[0] register and, optionally, enabling the
interrupt for endpoint 0 by writing 1 to the UDP_IER register. The enumeration then begins by a control transfer.
• Configure the interrupt mask register which has been reset by the USB reset detection
• Enable the transceiver clearing the TXVDIS flag in the UDP_TXVC register.
In this state UDPCK and MCK must be enabled.
Warning: Each time an ENDBUSRES interrupt is triggered, the Interrupt Mask Register and UDP_CSR registers
have been reset.
35.5.3.4 From Default State to Address State
After a set address standard device request, the USB host peripheral enters the address state.
Warning: Before the device enters in address state, it must achieve the Status IN transaction of the control trans-
fer, i.e., the UDP device sets its new address once the TXCOMP flag in the UDP_CSR[0] register has been
received and cleared.
To move to address state, the driver software sets the FADDEN flag in the UDP_GLB_STAT register, sets its new
address, and sets the FEN bit in the UDP_FADDR register.
35.5.3.5 From Address State to Configured State
Once a valid Set Configuration standard request has been received and acknowledged, the device enables end-
points corresponding to the current configuration. This is done by setting the EPEDS and EPTYPE fields in the
UDP_CSRx registers and, optionally, enabling corresponding interrupts in the UDP_IER register.
35.5.3.6 Entering in Suspend State
When a Suspend (no bus activity on the USB bus) is detected, the RXSUSP signal in the UDP_ISR register is set.
This triggers an interrupt if the corresponding bit is set in the UDP_IMR register.This flag is cleared by writing to the
UDP_ICR register. Then the device enters Suspend Mode.
In this state bus powered devices must drain less than 500uA from the 5V VBUS. As an example, the microcon-
troller switches to slow clock, disables the PLL and main oscillator, and goes into Idle Mode. It may also switch off
other devices on the board.
The USB device peripheral clocks can be switched off. Resume event is asynchronously detected. MCK and
UDPCK can be switched off in the Power Management controller and the USB transceiver can be disabled by set-
ting the TXVDIS field in the UDP_TXVC register.
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
516