41.6.14.3 Entering Attached State

When no device is connected, the USB FSDP and FSDM signals are tied to GND by 15 KΩ pulldowns integrated in the hub downstream ports. When a device is attached to an hub downstream port, the device connects a 1.5 KΩ pullup on FSDP. The USB bus line goes into IDLE state, FSDP is pulled up by the device 1.5 KΩ resistor to 3.3V and FSDM is pulled down by the 15 KΩ resistor to GND of the host.

After pullup connection, the device enters the powered state. The transceiver remains disabled until bus activity is detected.

In case of low power consumption need, the device can be stopped. When the device detects the VBUS, the software must enable the USB transceiver by enabling the EN_UDPHS bit in UDPHS_CTRL register.

The software can detach the pullup by setting DETACH bit in UDPHS_CTRL register.