Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet

1017

SAM4S Series [DATASHEET]

Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14

To enable integrated pull-up, the PUON bit in the UDP_TXVC register must be set. 
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 pull-up 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.

After its connection to a USB host, the USB device waits for an end-of-bus reset. The unmaskable flag 

ENDBUSRES is set in the UDP_ISR and an interrupt is triggered. 
Once the ENDBUSRES interrupt has been triggered, the device enters Default State. In this state, the UDP 

software must:



Enable the default endpoint, setting the EPEDS flag in the UDP_CSR0 and, optionally, enabling the interrupt 

for endpoint 0 by writing 1 to the UDP_IER. 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.

: Each time an ENDBUSRES interrupt is triggered, the Interrupt Mask Register and UDP_CSRs have 

been reset.

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 

transfer, i.e., the UDP device sets its new address once the TXCOMP flag in the UDP_CSR0 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.

Once a valid Set Configuration standard request has been received and acknowledged, the device enables 

endpoints corresponding to the current configuration. This is done by setting the EPEDS and EPTYPE fields in the 

UDP_CSRx and, optionally, enabling corresponding interrupts in the UDP_IER.

When a Suspend (no bus activity on the USB bus) is detected, the RXSUSP signal in the UDP_ISR is set. This 

triggers an interrupt if the corresponding bit is set in the UDP_IMR. This flag is cleared by writing to the UDP_ICR. 

Then the device enters Suspend Mode.
In this state bus powered devices must drain no more than 2.5 mA from the 5V VBUS. As an example, the 

microcontroller 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 

setting the TXVDIS field in the UDP_TXVC register.

: Read, write operations to the UDP registers are allowed only if MCK is enabled for the UDP peripheral. 

Switching off MCK for the UDP peripheral must be one of the last operations after writing to the UDP_TXVC 

register and acknowledging the RXSUSP.