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NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
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Revision V1.30
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[11:10]
LSTS
Line Status (RO)
These bits reflect the current logical levels of the D+ (bit 11) and D- (bit 10) signal lines.
These bits are used for detection of low-speed USB devices prior to the port reset and
enable sequence. This field is valid only when the port enable bit is zero and the current
connect status bit is set to a one.
The encoding of the bits are:
Bits[11:10] USB State Interpretation
00 = SE0 Not Low-speed device, perform EHCI reset.
01 = K-state Low-speed device, release ownership of port.
10 = J-state Not Low-speed device, perform EHCI reset.
11 = Undefined Not Low-speed device, perform EHCI reset.
This value of this field is undefined if Port Power is zero.
[9]
Reserved
Reserved.
[8]
PRST
Port Reset (R/W)
When software writes a one to this bit (from a zero), the bus reset sequence as defined in
the USB Specification Revision 2.0 is started. Software writes a zero to this bit to terminate
the bus reset sequence. Software must keep this bit at a one long enough to ensure the
reset sequence, as specified in the USB Specification Revision 2.0, completes.
Note:
when software writes this bit to a one, it must also write a zero to the Port Enable bit.
Note that when software writes a zero to this bit there may be a delay before the bit status
changes to a zero. The bit status will not read as a zero until after the reset has completed.
If the port is in high-speed mode after reset is complete, the host controller will
automatically enable this port (e.g. set the Port Enable bit to a one). A host controller must
terminate the reset and stabilize the state of the port within 2 milliseconds of software
transitioning this bit from a one to a zero. For example: if the port detects that the attached
device is high-speed during reset, then the host controller must have the port in the
enabled state within 2ms of software writing this bit to a zero.
The HCHalted bit in the USBSTS register should be a zero before software attempts to use
this bit. The host controller may hold Port Reset asserted to a one when the HCHalted bit
is a one.
This field is zero if Port Power is zero.
0 = Port is not in Reset.
1 = Port is in Reset.