NRF52820-QDAA-R datasheet(372/437 Pages) NORDIC

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Peripherals

Attached

Powered

USB power

lost

USB power

applied

Default

Address

Configured

Suspended

USB reset

Address

assigned

Device

configured

Momentary

power

interruption

USB reset

Device

deconfigured

Bus inactive

Bus activity

Bus inactive

Bus activity

Bus inactive

Bus activity

Bus inactive

Bus activity

Figure 136: Device state diagram

The device must change state according to host-initiated traffic and USB bus states. It is up to the software

to implement a state machine that matches the above definition. To detect the presence or absence of

USB supply (VBUS), two events USBDETECTED and USBREMOVED can be used to implement the state

machine. For more details on these events, see USB supply on page 54.

As a general rule when implementing the software, the host behavior shall never be assumed to be

predictable. In particular the sequence of commands received during an enumeration. The software shall

always react to the current bus conditions or commands sent by the host.

6.26.2 USB terminology

The USB specification defines bus states, rather than logic levels on the D+ and D- lines.

For a full speed device, the bus state where the D+ line is high and the D- line is low is defined as the J

state. The bus state where D+ is low and D- high is called the K state.

An idle bus, where D+ and D- lines are only polarized through the pull-up on D+ and pull-downs on the

host side, will be in J state.

Both lines low are called SE0 (single-ended 0), and both lines high SE1 (single-ended 1).

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NRF52820-QDAA-R Datasheet(PDF) 372 Page - Nordic Semiconductor

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