AS4LC2M8S1 datasheet(12/28 Pages) ALSC

12 / 28 page

ALLIANCE SEMICONDUCTOR

7/5/00

AS4LC2M8S1

AS4LC1M16S1

Initialize and load mode register

* DQM represents DQML and DQMH. DQML controls the lower byte, and DQMH controls the upper byte.

† The Mode Register may be loaded prior to the auto refresh cycles if desired.

ƒ Outputs are guaranteed High-Z after command is issued.

Clock suspend/power

down mode exit

CKE = high

Resume internal clock operation by asserting CKE high before the

rising edge of CLK. Subsequent commands can be issued one clock

cycle after the end of the Exit command.

Auto refresh

CS = RAS = CAS = low; WE =

CKE = high; A0~A11 = don’t

care

SDRAM storage cells must be refreshed every 64 ms to maintain data

integrity. Use the auto refresh command to accomplish the refreshing

of all rows in both banks of the SDRAM. The row address is provided

by an internal counter which increments automatically. Auto refresh

can only be asserted when both banks are idle and the device is not in

the power down mode. The time required to complete the auto refresh

operation is tRC(min). Use NOPs in the interim until the auto refresh

operation is complete. Both banks will be in the idle state after this

operation.

Self refresh

CS = RAS = CAS = CKE = low;

WE = high; A0~A11 = don’t

care

Self refresh is another mode for refreshing SDRAM cells. In this mode,

refresh address and timing are provided internally. Self refresh entry is

allowed only when both banks are idle. The internal clock and all input

buffers with the exception of CKE are disabled in this mode. Exit self

refresh by restarting the external clock and then asserting CKE high.

NOPs must follow for a time of tRC(min) for the SDRAM to reach the

idle state where normal operation is allowed. If burst auto refresh is

used in normal operation, burst 2048 auto refresh cycles immediately

after exiting self refresh.

Command

Pin settings

Description

CLK

CKE

COMMAND

DQM*

ADDRESS

Tp+1

Tp+2

Tp+3

tCH

tCL

tCK

tCKS

tCKH

NOP

AUTO REFRESH

NOP

tCMH

tCMS

AUTO REFRESH

NOP NOP

LOAD MODE

ACTIVE

CODE

tAS

tAH

BANK ROW

NOP NOP

High Z

T=200

µs

(min)

Power up:

VDD and

CLK stable.

tRP

Precharge

all banks.

(8 AUTO REFRESH

tRCAR

Program Mode Register†ƒ

tMRD

PRECHARGE

A10=HIGH

ALL

AUTO REFRESH

CYCLES)

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