AS4SD4M16(2001) Просмотр технического описания (PDF) - Austin Semiconductor

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AS4SD4M16
(Rev.:2001)

4 Meg x 16 SDRAM Synchronous DRAM Memory

Austin Semiconductor 

Austin Semiconductor, Inc.

SDRAM

AS4SD4M16

COMMAND INHIBIT

The COMMAND INHIBIT function prevents new

commands from being executed by the SDRAM, regardless of

whether the CLK signal is enabled. The SDRAM is effectively

deselected. Operations already in progress are not affected.

NO OPERATION (NOP)

The NO OPERATION (NOP) command is used to per-

form a NOP to an SDRAM which is selected (CS\ is LOW). This

prevents unwanted commands from being registered during

idle or wait states. Operations already in progress are not af-

fected.

LOAD MODE REGISTER

The Mode Register is loaded via inputs A0-A11. See

Mode Register heading in the Register Definition section. The

LOAD MODE REGISTER command can only be issued when

all banks are idle, and a subsequent executable command can-

not be issued until tMRD is met.

ACTIVE

The ACTIVE command is used to open (or activate) a

row in a particular bank for a subsequent access. The value on

the BA0, BA1 inputs selects the bank, and the address pro-

vided on inputs A0-A11 selects the row. This row remains ac-

tive (or open) for accesses until a PRECHARGE command is

issued to that bank. A PRECHARGE command must be issued

before opening a different row in the same bank.

WRITE

The WRITE command is used to initiate a burst write

access to an active row. The value on the BA0, BA1 inputs

selects the bank, and the address provided on inputs A0-A7

(x16) selects the starting column location. The value on input

A10 determines whether or not AUTO PRECHARGE is used. If

AUTO PRECHARGE is selected, the row being accessed will

be precharged at the end of the WRITE burst; if AUTO

PRECHARGE is not selected, the row will remain open for sub-

sequent accesses. Input data appearing on the DQs is written

to the memory array subject to the DQM input logic level ap-

pearing coincident with the data. If a given DQM signal is

registered LOW, the corresponding data will be written to

memory; if the DQM signal is registered HIGH, the correspond-

ing data inputs will be ignored, and a WRITE will not be ex-

ecuted to that byte/column location.

PRECHARGE

The PRECHARGE command is used to deactivate the

open row in a particular bank or the open row in all banks. The

bank(s) will be available for a subsequent row access a speci-

fied time (tRP) after the PRECHARGE command is issued. Input

A10 determines whether one or all banks are to be precharged,

and in the case where only one bank is to be precharged, inputs

BA0, BA1 select the bank. Otherwise BA0, BA1 are treated as

“Don’t Care.” Once a bank has been precharged, it is in the idle

state and must be activated prior to any READ or WRITE com-

mands being issued to that bank.

READ

The READ command is used to initiate a burst read

access to an active row. The value on the BA0, BA1 inputs

selects the bank, and the address provided on inputs A0-A7

(x16) selects the starting column location. The value on input

A10 determines whether or not AUTO PRECHARGE is used. If

AUTO PRECHARGE is selected, the row being accessed will

be precharged at the end of the READ burst; if AUTO

PRECHARGE is not selected, the row will remain open for sub-

sequent accesses. Read data appears on the DQs subject to

the logic level on the DQM inputs two clocks earlier. If a given

DQM signal was registered HIGH, the corresponding DQs will

be High-Z two clocks later; if the DQM signal was registered

LOW, the DQs will provide valid data.

AUTO PRECHARGE

AUTO PRECHARGE is a feature which performs the

same individual-bank PRECHARGE function described above,

without requiring an explicit command. This is accomplished

by using A10 to enable AUTO PRECHARGE in conjunction

with a specific READ or WRITE command. A precharge of the

bank/row that is addressed with the READ or WRITE com-

mand is automatically performed upon completion of the READ

or WRITE burst, except in the full-page burst mode, where

AUTO PRECHARGE does not apply. AUTO PRECHARGE is

nonpersistent in that it is either enabled or disabled for each

individual READ or WRITE command.

AUTO PRECHARGE ensures that the precharge is

initiated at the earliest valid stage within a burst. The user must

not issue another command to the same bank until the precharge

time (tRP) is completed. This is determined as if an explicit

PRECHARGE command was issued at the earliest possible time,

as described for each burst type in the Operation section of this

data sheet.

AS4SD4M16

Rev. 1.5 10/01

10

Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.

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