FireLink USB
82C862
912-2000-030
Revision: 1.0
Page 16
®
4.4.5
Stopping the Internal USB Clocks
The 82C862 device is equipped with PCI Power Management registers. When either function is set to D3hot mode, its internal
USB clock is switched off to effect a significant reduction in power consumption. Returning the system to D0 will restart the
internal USB clock.
4.4.6
Power Control Modes
The 82C862 pinout includes the following signals for controlling and monitoring USB power for the respective USB port:
• PWRON1-4# are active-low outputs to turn USB power on.
• PWRFLT1-4# are active-low inputs to detect over current.
At design time, it must be decided whether these control and monitoring signals will be used independently on a per-port basis
(ideal situation), or paired together (for lower component cost). Consequently, the chip can strap into one of two power control
modes:
• Individual PWRON# and PWRFLT# - entered when PWRON2# is sensed high at reset
• Global PWRON# and PWRFLT# - entered when PWRON2# is sensed low at reset.
The 82C862 part supports two modes for turning on power to the respective USB ports: Global and Individual (per-port). This
logic is contained in the Root Hub partition of each USB controller module, and consists of a portion for the Root Hub itself as
well as portions for each individual port. The operation of Global and Individual power switching is explained below.
Global Power Switching is the mode that is supported in the original 82C861 design. In this mode either PWRON1# or
PWRON2# can be used to turn on power for both ports on USB Host 1, and either PWRON3# or PWRON4# can be used to
turn on power for both ports USB Host 2. When supporting this mode the following registers are of significance:
Register
Field
Value or Function
HcRhDescriptorA
NoPowerSwitching
MEMOFST 49h[1]
0: Ports are power switched
HcRhDescriptorA
PowerSwitchingMode
MEMOFST 49h[0]
0: All ports are powered at the same time
HcRhDescriptorB
PortPowerControlMask
MEMOFST 4Eh[2:1]
Not Used
HcRhStatus
ClearGlobalPower (write)
MEMOFST 50h[0]
This bit is written to ‘1’ to turn OFF power to all ports.
HcRhStatus
SetGlobalPower (write)
MEMOFST 52h[0]
This bit is written to ‘1’ to turn ON power to all ports.
HcRhPort1Status
HcRhPort2Status
PortPowerStatus (read)
MEMOFST 55h[0] port 1
MEMOFST 59h[0] port 2
0=port power is off
1=port power is on
Only Set/ClearGlobalPower controls this bit
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