82551QM Datasheet, PDF (34/120 Pages) Intel Corporation – Fast Ethernet Multifunction PCI/CardBus Controller

82551QM — Networking Silicon
5.3.1.4.1 Auxiliary Power Signal
The 82551QM senses whether it is connected to the PCI power supply or to an auxiliary power
supply (V_AUX) through the FLA1/AUXPWR pin. The auxiliary power detection pin (multiplexed
with FLA1) is sampled when the 82551QM power-on reset is active. An external pull-up resistor
should be connected to the 82551QM if it is fed by V_AUX; otherwise, the FLA1/AUXPWR pin
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 9.1.20, “Power Management Capabilities
Register”.
5.3.1.4.2 Alternate Reset Signal
The 82551QM’s ALTRST# input pin functions as a power-on reset input. Following ALTRST#
being driven low, the 82551QM 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 82551QM’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 82551QM power-on reset function and is also used for
sampling configuration inputs.
5.3.1.4.3 Isolate Signal
When the 82551QM is connected to V_AUX, it can be powered on while the PCI bus is powered off.
In this case, the 82551QM isolates itself from the PCI bus. The 82551QM 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 82551QM isolates itself from the PCI bus.
During this state, the 82551QM 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 Reset Signal
The 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)
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Datasheet