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Intel® 6400/6402 Advanced Memory Buffer Datasheet

DDR Interface

3.7

S3 State Background Description

S3 is a platform power down state where DRAM memory contents are preserved while

the rest of the platform powers down. This state is described more formally in the

Advanced Configuration and Power Interface Specification. It is much like the Standby

mode on mobile computers.

Functionally, the requirement for an AMB is that after a sequence in which:

• AMBS3 Recovery state is stored by the host,

• DRAMs are put into Self-Refresh,

• RESET# is asserted,

• Vcc (1.5 V), Vtt (0.9 V) and VddSPD(3.3 V) are powered down,

The contents of memory on the DIMM are preserved until S3 Recovery. Recovery

requires that the memory on the DIMM be restored without losing data integrity.

The recovery sequence is much the same as an initial power on with the exceptions of:

• Vdd is already powered on

• DDR interface state is restored from stored register values (since no calibration

which might compromise memory content is allowed)

To minimize DIMM current, VCC should be powered up during VTT transitions. The AMB

determines that it is in the S3 mode by checking that VDD (1.8 V) is powered up and

that VCC (1.5 V) is powered off. When in S3 the AMB drives all command/address

outputs (including CKE, ODT, and CLK) to a low. This keeps the DRAM in auto-refresh

and helps prevent DRAM data corruption. When coming out of the S3 mode, if the

system brings VTT (0.9 V) up before VCC the AMB will drive low into the VTT pull-up

circuitry. This causes significant current (approximately two times average but still

normal) to flow from VTT into the AMB until VCC is powered up and the AMB comes out

of S3.

Figure 3-1. Nominal Turnaround Time Timing Diagram

DQS

Preamble A

Preamble B

Data

A-0

Data

A-2

Data

A-3

Data

A-1

Data

B-0

Data

B-1

Data

B-2

Data

B-3

Clock

DQS

Preamble R

(read)

Preamble W

(write)

Data

R-0

Data

R-2

Data

R-3

Data

R-1

Data

W-0

Data

W-1

Data

W-2

Data

W-3

Clock

Postamble

DQS

Preamble R

(read)

Preamble W

(write)

Data

R-0

Data

R-2

Data

R-3

Data

R-1

Data

W-0

Data

W-1

Data

W-2

Data

W-3

Clock

Postamble

Read to Read turnaround (nominal)

Read to Write turnaround (nominal)

Write to Read turnaround (nominal)

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