USBN9604 datasheet(22/60 Pages) NSC

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6.0

Functional Description

6.1

FUNCTIONAL STATES

6.1.1

Line Condition Detection

At any given time, the device is in one of the following states (see Section 6.1.2 for the functional state transitions):

• NodeOperational

Normal operation

• NodeSuspend

Device operation suspended due to USB inactivity

• NodeResume

Device wake-up from suspended state

• NodeReset

Device reset

The NodeSuspend, NodeResume, or NodeReset line condition causes a transition from one operating state to another.

These conditions are detected by specialized hardware and reported via the Alternate Event (ALTEV) register. If interrupts

are enabled, an interrupt is generated upon the occurrence of any of the specified conditions.

NodeOperational

This is the normal operating state of the device. In this state, the node is configured for operation on the USB bus.

NodeSuspend

A USB device is expected to enter NodeSuspend state when 3 mS have elapsed without any detectable bus activity. The

device looks for this event and signals it by setting the SD3 bit in the ALTEV register, which causes an interrupt, if enabled,

to be generated. The firmware should respond by putting the device into the NodeSuspend state.

The device can resume normal operation under firmware control in response to a local event at the host controller. It can

wake up the USB bus via a NodeResume, or when detecting a resume command on the USB bus, which signals an interrupt

to the host controller.

NodeResume

If the host has enabled remote wake-ups from the node, the device can initiate a remote wake-up.

Once the firmware detects the event, which wakes up the bus, it releases the device from NodeSuspend state by initiating

a NodeResume on the USB using the NFSR register. The node firmware must ensure at least 5 mS of Idle on the USB.

While in NodeResume state, a constant “K” is signalled on the USB. This should last for at least 1 mS and no more than 5

mS, after which the USB host should continue sending the NodeResume signal for at least an additional 20 mS, and then

completes the NodeResume operation by issuing the End Of Packet (EOP) sequence.

To successfully detect the EOP, the firmware must enter USB NodeOperational state by setting the NFSR register.

If no EOP is received from the host within 100 mS, the software must reinitiate NodeResume.

NodeReset

When detecting a NodeResume or NodeReset signal while in NodeSuspend state, the device can signal this to the main

controller by generating an interrupt.

USB specifications require that a device must be ready to respond to USB tokens within 10 mS after wake-up or reset.

6.1.2

Functional State Transition

Figure 18 shows the device states and transitions, as well as the conditions that trigger each transition. All state transitions

are initiated by the firmware.

USBN9604 Datasheet(PDF) 22 Page - National Semiconductor (TI)

USBN9604 Datasheet(HTML) 22 Page - National Semiconductor (TI)

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