W3E64M72S-XBX

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White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com

White Electronic Designs

June 2005

Rev. 0

ADVANCED

White Electronic Designs Corp. reserves the right to change products or specifications without notice.

COMMANDS

The Truth Table provides a quick reference of available

commands. This is followed by a written description of

each command.

DESELECT

The DESELECT function (CS# High) prevents new

commands from being executed by the DDR SDRAM.

The SDRAM is effectively deselected. Operations already

in progress are not affected.

NO OPERATION (NOP)

The NO OPERATION (NOP) command is used to perform

a NOP to the selected DDR SDRAM (CS# is LOW while

RAS#, CAS#, and WE# are high). This prevents unwanted

commands from being registered during idle or wait states.

Operations already in progress are not affected.

LOAD MODE REGISTER

The Mode Registers are loaded via inputs A0-12. The

LOAD MODE REGISTER command can only be issued

when all banks are idle, and a subsequent executable

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 provided on inputs A0-12 selects the row. This row

remains active (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.

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 A0-9, 11

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 subsequent accesses.

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 A0-9, 11 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 subsequent accesses. Input

data appearing on the DQ is written to the memory array

subject to the DQM input logic level appearing 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 corresponding data

inputs will be ignored, and a WRITE will not be executed

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

issued. Except in the case of concurrent auto precharge,

where a READ or WRITE command to a different bank is

allowed as long as it does not interrupt the data transfer

in the current bank and does not violate any other timing

parameters. 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 commands

being issued to that bank. A PRECHARGE command will

be treated as a NOP if there is no open row in that bank

(idle state), or if the previously open row is already in the

process of precharging.

AUTO PRECHARGE

AUTO PRECHARGE is a feature which performs the

same individual-bank PRECHARGE function described

above, but 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 command is automatically performed

upon completion of the READ or WRITE burst. AUTO