NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
- 741 -
Revision V1.30
NUC97
0
T
E
CHNIC
A
L
RE
F
E
RE
N
CE
MA
NUA
L
[3]
PEC
Port Enable/Disable Change (R/WC)
For the root hub, this bit gets set to a one only when a port is disabled due to the
appropriate conditions existing at the EOF2 point (See Chapter 11 of the USB Specifica-
tion for the definition of a Port Error). Software clears this bit by writing a 1 to it.
This field is zero if Port Power is zero.
0 = No change.
1 = Port enabled/disabled status has changed.
[2]
PE
Port Enabled/Disabled (R/W)
Ports can only be enabled by the host controller as a part of the reset and enable.
Software cannot enable a port by writing a one to this field. The host controller will only set
this bit to a one when the reset sequence determines that the attached device is a high-
speed device.
Ports can be disabled by either a fault condition (disconnect event or other fault condition)
or by host software. Note that the bit status does not change until the port state actually
changes. There may be a delay in disabling or enabling a port due to other host controller
and bus events.
When the port is disabled (0b) downstream propagation of data is blocked on this port,
except for reset.
This field is zero if Port Power is zero.
0 = Disable.
1 = Enable.
[1]
CSC
Connect Status Change (R/W)
Indicates a change has occurred in the port’s Current Connect Status. The host controller
sets this bit for all changes to the port device connect status, even if system software has
not cleared an existing connect status change. For example, the insertion status changes
twice before system software has cleared the changed condition, hub hardware will be
“setting” an already-set bit (i.e., the bit will remain set).Software sets this bit to 0 by writing
a 1 to it.
This field is zero if Port Power is zero.
0 = No change.
1 = Change in Current Connect Status.
[0]
CCS
Current Connect Status (RO)
This value reflects the current state of the port, and may not correspond directly to the
event that caused the Connect Status Change bit (Bit 1) to be set.
This field is zero if Port Power is zero.
0 = No device is present.
1 = Device is present on port.