A48P4616
Features
CAS Latency and Frequency
CAS
Latency
2
2.5
3
Maximum Operating Frequency (MHz)
DDR400 (5T)
-
166
200
DDR333 (6K)
133
166
-
DQ
S
is edge-aligned with data for reads and is center-
aligned with data for writes.
Differential clock inputs (CK and CK)
Four internal banks for concurrent operation.
Data mask (DM) for write data.
DLL aligns DQ and DQ
S
transitions with CK transitions.
Commands entered on each positive CK edge; data and
data mask referenced to both edges of DQ
S
.
Burst lengths: 2, 4, or 8
CAS Latency: 2/2.5(DDR333), 2.5/3(DDR400)
Auto Precharge option for each burst access
Auto Refresh and Self Refresh Modes
7.8µs Maximum Average Periodic Refresh Interval
2.5V (SSTL_2 compatible) I/O
V
DD
= V
DDQ
= 2.5V ± 0.2V (DDR333)
V
DD
= V
DDQ
= 2.6V ± 0.1V (DDR400)
Available in Halogen and Lead Free packaging
DDR 256M bit, die C, based on 110nm design rules.
Double data rate architecture: two data transfers per
clock cycle.
Bidirectional data strobe (DQ
S
) is transmitted and
received with data, to be used in capturing data at the
receiver.
General Description
The 256Mb DDR SDRAM uses a double-data-rate architec-
ture to achieve high-speed operation. The double data rate
architecture is essentially a 2n prefetch architecture with an
interface designed to transfer two data words per clock cycle
at the I/O pins. A single read or write access for the 256Mb
DDR SDRAM effectively consists of a single 2n-bit wide, one
clock cycle data transfer at the internal DRAM core and two
corresponding n-bit wide, one-half-clock-cycle data transfers
at the I/O pins.
A bidirectional data strobe (DQ
S
) is transmitted externally,
along with data, for use in data capture at the receiver. DQ
S
is a strobe transmitted by the DDR SDRAM during Reads
and by the memory controller during Writes. DQ
S
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 DQ
S
, as well
as to both edges of CK.
Read and write accesses to the DDR SDRAM are burst ori-
ented; 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 com-
mand. 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 func-
tion 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 architec-
ture of DDR SDRAMs allows for concurrent operation,
thereby providing high effective bandwidth by hiding row pre-
charge 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 com-patible.
The functionality described and the timing specifications
included in this data sheet are for the DLL Enabled mode of
operation.
Preliminary (September, 2005, Version 0.0)
1
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