NAT

The Node Attached indicates that this node is

 

ready to be detected as attached to USB.

 

When clear, the transceiver forces SE0 on the

 

USB node controller to prevent the hub (to

 

which this node is connected) from detecting

 

an attach event. After reset or when the USB

 

node is disabled, this bit is cleared to give the

 

device time before it must respond to com-

 

mands. After this bit has been set, the device

 

no longer drives the USB and should be ready

 

to receive Reset signaling from the hub.

 

0 – Node not ready to be detected as at-

 

tached.

 

1 – Node ready to be detected as attached.

18.3.2Node Functional State Register (NFSR)

The NFSR register reports and controls the current func- tional state of the USB node. The NFSR register provides read/write access. It is clear after reset.

7

2

1

0

 

Reserved

 

NFS

 

 

 

NFS

The Node Functional State bits set the node

 

state, as shown in Table 41. Software should

 

initiate all required state transitions according

to the respective status bits in the Alternate Event (ALTEV) register.

CP3BT26

 

 

Table 41 USB Functional States

 

 

 

NFS

Node State

Description

 

 

 

 

 

 

 

 

This is the USB Reset state. This is entered upon a module reset or by software upon

 

 

detection of a USB Reset. Upon entry, all endpoint pipes are disabled. DEF in the Endpoint

00

NodeReset

Control 0 (EPC0) register and AD_EN in the Function Address (FAR) register should be

 

 

cleared by software on entry to this state. On exit, DEF should be reset so the device

 

 

responds to the default address.

 

 

 

 

 

In this state, resume “K” signalling is generated. This state should be entered by software to

01

NodeResume

initiate a remote wake-up sequence by the device. The node must remain in this state for at

 

 

least 1 ms and no more than 15 ms.

 

 

 

10

NodeOperational

This is the normal operational state for operation on the USB bus.

 

 

 

 

 

Suspend state should be entered by software on detection of a Suspend event while in

 

 

Operational state. While in Suspend state, the transceivers operate in their low-power

11

NodeSuspend

suspend mode. All endpoint controllers and the bits TX_EN, LAST, and RX_EN are reset,

 

 

while all other internal states are frozen. On detection of bus activity, the RESUME bit in the

 

 

ALTEV register is set. In response, software can cause entry to NodeOperational state.

 

 

 

95

www.national.com

Page 95
Image 95
National CP3BT26 manual Node Functional State Register Nfsr, USB Functional States, Node State Description