Datasheet

SAM9G20
DS60001516A-page 670  2017 Microchip Technology Inc.
36.5.3.1 Not Powered State
Self powered devices can detect 5V VBUS using a PIO as described in the typical connection section. When the device is not connected
to a host, device power consumption can be reduced by disabling MCK for the UDP, disabling UDPCK and disabling the transceiver. DDP
and DDM lines are pulled down by 330 KΩ resistors.
36.5.3.2 Entering Attached State
When no device is connected, the USB DP and DM signals are tied to GND by 15 KΩ pull-down resistors integrated 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. To enable
integrated pullup, 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 pullup connection, the device enters the powered state. In this state, the UDPCK and MCK must be enabled in the Power Manage-
ment Controller. The transceiver can remain disabled.
36.5.3.3 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 ENDBUSRES 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 software 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. 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.
36.5.3.4 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 transfer, 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.
36.5.3.5 From Address State to Configured State
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 registers and, optionally, enabling
corresponding interrupts in the UDP_IER.
36.5.3.6 Entering in Suspend State
When a Suspend (no bus activity on the USB bus) is detected, the RXSUSP signal in the UDP_ISR 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 less than 500uA 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.
Warning: Read
, write ope
rations 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 and acknowledging the RXSUSP.
36.5.3.7 Receiving a Host Resume
In suspend mode, a resume event on the USB bus line is detected asynchronously, transceiver and clocks are disabled (however the
pullup shall not be removed).
Once the resume is detected on the bus, the WAKEUP signal in the UDP_ISR is set. It may generate an interrupt if the corresponding bit
in the UDP_IMR is set. This interrupt may be used to wake up the core, enable PLL and main oscillators and configure clocks.
Warning: Read, write operations to the UDP registers are allowed only if MCK is enabled for the UDP peripheral. MCK for the UDP must
be enabled before clearing the WAKEUP bit in the UDP_ICR and clearing TXVDIS in the UDP_TXVC register.