National CP3BT26 - Manual (Page 95)

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CP3
BT26
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.
18.3.2 Node 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.
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.
7 2 1 0
Reserved NFS
Table 41 USB Functional States
NFS Node State Description
00 NodeReset
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
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.
01 NodeResume
In this state, resume “K” signalling is generated. This state should be entered by software to
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.
11 NodeSuspend
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
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.