8.4.4 USB3.1 Modes

The TUSB1042I monitors the physical layer conditions like receiver termination, electrical idle, LFPS, and SuperSpeed signaling rate to determine the state of the USB3.1 interface. Depending on the state of the USB 3.1 interface, the TUSB1042I can be in one of four primary modes of operation when USB 3.1 is enabled (CTL0 = H or CTLSEL0 = 1b1): Disconnect, U2/U3, U1, and U0.

The Disconnect mode is the state in which TUSB1042I has not detected far-end termination on both upstream facing port (UFP) or downstream facing port (DFP). The disconnect mode is the lowest power mode of each of the four modes. The TUSB1042I remains in this mode until far-end receiver termination has been detected on both UFP and DFP. The TUSB1042I immediately exits this mode and enter U0 once far-end termination is detected.

Once in U0 mode, the TUSB1042I will redrive all traffic received on UFP and DFP. U0 is the highest power mode of all USB3.1 modes. The TUSB1042I remains in U0 mode until electrical idle occurs on both UFP and DFP. Upon detecting electrical idle, the TUSB1042I immediately transitions to U1.

The U1 mode is the intermediate mode between U0 mode and U2/U3 mode. In U1 mode, the TUSB1042I UFP and DFP receiver termination remains enabled. The UFP and DFP transmitter DC common mode is maintained. The power consumption in U1 is similar to power consumption of U0.

Next to the disconnect mode, the U2/U3 mode is next lowest power state. While in this mode, the TUSB1042I periodically performs far-end receiver detection. Anytime the far-end receiver termination is not detected on either UFP or DFP, the TUSB1042I leaves the U2/U3 mode and transitions to the Disconnect mode. It also monitors for a valid LFPS. Upon detection of a valid LFPS, the TUSB1042I immediately transitions to the U0 mode. In U2/U3 mode, the TUSB1042I receiver terminations remain enabled but the TX DC common mode voltage is not maintained.