Intel 820E 6. System Design Considerations

Intel® 820E Chipset

Design Guide 183

6. System Design Considerations

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 VSB. 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 VSB (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 VSB usually is derived (on the

motherboard) from 5 VSB using a voltage regulator. (On the Intel 820E chipset

reference board, 3.3 VSB 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.