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Intel
®
820E Chipset
R
Design Guide 183
6. System Design Considerations
6.1. Power Delivery
6.1.1. Terminology and Definitions
Term Definition
Suspend to
RAM (STR)
In the STR state, the system state is stored in main memory and all unnecessary
system logic is turned off. Only main memory and logic required to wake the
system remain powered. This state is used in the Customer Reference Board to
satisfy the S3 ACPI power management state.
Full-power
operation
During full-power operation, all components on the motherboard remain powered.
Note that full-power operation includes both the full-on operating state and the S1
(
processor Stop Grant state) state.
Suspend
operation
During suspend operation, power is removed from some components on the
motherboard. The customer reference board supports two suspend states: Suspend
to RAM (S3) and Soft-Off (S5).
Power rails An ATX power supply has 6 power rails: +5 V, -5 V, +12 V, -12 V, +3.3 V, and
5 V
SB
. In addition to these power rails, several other power rails are created with
voltage regulators on the Intel 820E chipset reference board.
Core power rail These power rails are on only during full-power operation. These power rails are on
when the PSON signal is asserted to the ATX power supply. The following core
power rails are distributed directly from the ATX power supply: ±5 V, ±12 V, and
+3.3 V.
Standby power
rail
These power rails are on during the suspend operation. (These rails also are on
during full-power operation.) These rails are on at all times (when the power supply
is plugged into AC power). The only standby power rail that is distributed directly
from the ATX power supply is 5 V
SB
(5 V standby). Other standby rails are created
with voltage regulators on the motherboard.
Derived power
rail
A derived power rail is any power rail generated from another power rail using an
on-board voltage regulator. For example, 3.3 V
SB
usually is derived (on the
motherboard) from 5 V
SB
using a voltage regulator. (On the Intel 820E chipset
reference board, 3.3 V
SB
is derived from 5V_DUAL.)
Dual power rail A dual power rail is derived from different rails at different times (depending on the
power state of the system). Usually, a dual power rail is derived from a standby
supply during the suspend operation and is derived from a core supply during full-
power operation. Note that the voltage on a dual power rail may be misleading.