DDR SDRAM

DDR SDRAM 256Mb E-die (x4, x8)

Rev. 1.3 April, 2005

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. Taking CKE Low provides PRECHARGE POWER-

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

ACTIVE in any bank). CKE is synchronous for POWER-DOWN entry and exit, and for SELF

REFRESH entry. CKE is asynchronous for SELF REFRESH exit, and for output disable. CKE

must be maintained high throughput READ and WRITE accesses. Input buffers, excluding CK,

CK and CKE are disabled during POWER-DOWN. Input buffers, excluding CKE are disabled

during SELF REFRESH. CKE is an SSTL_2 input, but will detect an LVCMOS Low level after

tialization sequence, it must be maintained for proper operation of the CKE receiver. For

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.

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. Although DM pins are input only, the DM loading matches the DQ and DQS

loading. DM may be driven high, low, or floating during READs.

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 [0 : 12]

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 mem-

ory array in the respective bank. A10 is sampled during a PRECHARGE command to deter-

mine 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

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.

NC

-

No Connect : No internal electrical connection is present.

VDDQ

Supply

DQ Power Supply : +2.5V ± 0.2V.

VSSQ

Supply

DQ Ground.

VDD

Supply

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

VSS

Supply

Ground.

VREF

Input

SSTL_2 reference voltage.

Input/Output Function Description