Networking Silicon — 82551IT
5.3.1.4.1 Auxiliary Power Signal
The 82551IT senses whether it is connected to the PCI power supply or to an auxiliary power
supply (V ) through the FLA1/AUXPWR pin. The auxiliary power detection pin (multiplexed
AUX
with FLA1) is sampled when the 82551IT power-on reset is active. An external pull-up resistor
should be connected to the 82551IT if it is fed by V ; otherwise, the FLA1/AUXPWR pin
AUX
should be left floating. The presence of AUXPWR affects the value reported in the Power
Management Capability Register (PCI Configuration Space, offset DEh). The Power Management
Capability Register is described in more detail in Section 7.1.19, “Power Management Capabilities
Register”.
5.3.1.4.2 Alternate Reset Signal
The 82551IT’s ALTRST# input pin functions as a power-on reset input. Following ALTRST#
being driven low, the 82551IT is initialized to a known state. While this function is required, this
pin is not needed for it. Since this functionality is provided by the 82551IT’s internal power-on
reset signal, this pin should be pulled high to the main digital power supply.
Note: A separate internal power-on reset signal is generated when power is applied to the device. This
signal is active while it provides the 82551IT power-on reset function and is also used for sampling
configuration inputs.
5.3.1.4.3 Isolate Signal
When the 82551IT is connected to V
, it can be powered on while the PCI bus is powered off. In
AUX
this case, the 82551IT isolates itself from the PCI bus. The 82551IT has a dedicated ISOLATE# pin
that must be connected to the PCI Reset signal. Whenever the PCI Bus is in the B3 state, the PCI
Reset signal becomes active and the 82551IT isolates itself from the PCI bus. During this state, the
82551IT ignores all PCI signals including the RST# and CLK input signals. It also tristates all PCI
outputs, except the PME# signal. In the transition to an active PCI power state (in other words,
from B3 bus power state to B0 bus power state), the PCI Reset signal shifts high. This generates an
internal hardware reset, which initializes the device (described in Section 5.1.1, “Initialization
Effects”).
Some designs in existence may implement the previous recommendations for the RST#,
ISOLATE# and ALTRST# input pins. In these cases, the PCI Reset signal is connected to the RST#
pin, the PCI power source’s stable power (power good) to the ISOLATE# pin, and the auxiliary
power source’s stable power (auxiliary power good) to the ALTRST# pin. It is not necessary for
existing working designs to make changes for these signals; however, it is recommended that the
changes contained in this document should be included when possible. New designs should
implement the recommendations contained in this document.
5.3.1.4.4 PCI Reset Signal
The PCI RST# signal can be activated in one of the following cases:
• Power-up
• Warm boot
• Wake-up (B3 to B0 transition)
• Set to power-down (B0 to B3 transition)
Datasheet
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INTEL [ INTEL ]
