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256Mb

DDR SDRAM

Rev. 2.2 Mar. ’03

Input/Output Function Description

SYMBOL

TYPE

DESCRIPTION

CK, CK

Input

Clock : CK and CK are differential clock inputs. All address and control input signals are sam-

pled on the positive edge of CK and negative edge of CK. Output (read) data is referenced to

both edges of CK. Internal clock signals are derived from CK/CK.

CKE

Input

Clock Enable : CKE HIGH activates, and CKE LOW deactivates internal clock signals, and

device input buffers and output drivers. Deactivating the clock provides PRECHARGE

POWER-DOWN and SELF REFRESH operation (all banks idle), or ACTIVE POWER-DOWN

(row ACTIVE in any bank). CKE is synchronous for all functions except for disabling outputs,

which is achieved asynchronously. Input buffers, excluding CK, CK and CKE are disabled

during power-down and self refresh modes, providing low standby power. CKE will recognize

an LVCMOS LOW level prior to VREF being stable on power-up.

CS

Input

Chip Select : CS enables(registered LOW) and disables(registered HIGH) the command

decoder. All commands are masked when CS is registered HIGH. CS provides for external

bank selection on systems with multiple banks. CS is considered part of the command code.

RAS, CAS, WE

Input

Command Inputs : RAS, CAS and WE (along with CS) define the command being entered.

LDM,(U)DM

Input

Input Data Mask : DM is an input mask signal for write data. Input data is masked when DM is

sampled HIGH along with that input data during a WRITE access. DM is sampled on both

edges of DQS. DM pins include dummy loading internally, to matches the DQ and DQS load-

ing. For the x16, LDM corresponds to the data on DQ0-DQ7 ; UDM correspons to the data on

DQ8-DQ15.

BA0, BA1

Input

Bank Addres Inputs : BA0 and BA1 define to which bank an ACTIVE, READ, WRITE or PRE-

CHARGE command is being applied.

A [n : 0]

Input

Address Inputs : Provide the row address for ACTIVE commands, and the column address

and AUTO PRECHARGE bit for READ/WRITE commands, to select one location out of the

memory array in the respective bank. A10 is sampled during a PRECHARGE command to

determine whether the PRECHARGE applies to one bank (A10 LOW) or all banks (A10

HIGH). If only one bank is to be precharged, the bank is selected by BA0, BA1. The address

inputs also provide the op-code during a MODE REGISTER SET command. BA0 and BA1

define which mode register is loaded during the MODE REGISTER SET command (MRS or

EMRS).

DQ

I/O

Data Input/Output : Data bus

LDQS,(U)DQS

I/O

Data Strobe : Output with read data, input with write data. Edge-aligned with read data, cen-

tered in write data. Used to capture write data. For the x16, LDQS corresponds to the data on

DQ0-DQ7 ; UDQS corresponds to the data on DQ8-DQ15.

NC

-

No Connect : No internal electrical connection is present.

Supply

DQ Power Supply : +2.5V ± 0.2V.

Supply

DQ Ground.

Supply

Power Supply : +2.5V ± 0.2V (device specific).

Supply

Ground.

Input

SSTL_2 reference voltage.