HYB25D256[400/800/160]B[T/C](L)
256-Mbit Double Data Rate SDRAM
Overview
A bidirectional data strobe (DQS) is transmitted externally, along with data, for use in data capture at the receiver.
DQS is a strobe transmitted by the DDR SDRAM during Reads and by the memory controller during Writes. DQS
is edge-aligned with data for Reads and center-aligned with data for Writes.
The 256Mb DDR SDRAM operates from a differential clock (CK and CK; the crossing of CK going HIGH and CK
going LOW is referred to as the positive edge of CK). Commands (address and control signals) are registered at
every positive edge of CK. Input data is registered on both edges of DQS, and output data is referenced to both
edges of DQS, as well as to both edges of CK.
Read and write accesses to the DDR SDRAM are burst oriented; accesses start at a selected location and
continue for a programmed number of locations in a programmed sequence. Accesses begin with the registration
of an Active command, which is then followed by a Read or Write command. The address bits registered
coincident with the Active command are used to select the bank and row to be accessed. The address bits
registered coincident with the Read or Write command are used to select the bank and the starting column location
for the burst access.
The DDR SDRAM provides for programmable Read or Write burst lengths of 2, 4 or 8 locations. An Auto
Precharge function may be enabled to provide a self-timed row precharge that is initiated at the end of the burst
access.
As with standard SDRAMs, the pipelined, multibank architecture of DDR SDRAMs allows for concurrent operation,
thereby providing high effective bandwidth by hiding row precharge and activation time.
An auto refresh mode is provided along with a power-saving power-down mode. All inputs are compatible with the
JEDEC Standard for SSTL_2. All outputs are SSTL_2, Class II compatible.
Note:The functionality described and the timing specifications included in this data sheet are for the DLL Enabled
mode of operation.
Data Sheet
7
Rev. 1.21, 2004-07
02102004-TSR1-4ZWW
QIMONDA [ QIMONDA AG ]
