Background
Page 7
© November 2008
Altera Corporation
AN 436: Using DDR3 SDRAM in Stratix III and Stratix IV Devices
f
For more information, refer to the
chapter of the
Stratix III
Device Handbook
and the
chapter of the
Stratix IV Device
Handbook.
DDR3 SDRAM Interface Pin Description
This section describes the DDR3 SDRAM interface pin description.
Clock Signals
DDR3 SDRAM devices use
CK
and
CK#
signals to clock the address and command
signals into the memory. Furthermore, the memory uses these clock signals to
generate the
DQS
signal during a read through the DLL inside the memory. The DDR3
SDRAM data sheet specifies the following timings:
■
t
DQSCK
is the skew between the
CK
or
CK#
signals and the DDR3 SDRAM-generated
DQS
signal
■
t
DSH
is the
DQS
falling edge from
CK
rising edge hold time
■
t
DSS
is the
DQS
falling edge from
CK
rising edge setup time
■
t
DQSS
is the positive
DQS
latching edge to
CK
rising edge
DDR3 SDRAM can use a daisy-chained CAC topology, so the memory clock arrives at
each chip at a different time. To compensate for this flight time skew between devices
across a typical DIMM, write leveling must be employed.
Strobes, Data, DM, and Optional ECC Signals
The
DQS
is bidirectional. Differential DQS strobe operation enables improved system
timing due to reduced crosstalk and less simultaneous switching noise on the strobe
output drivers. The
DQ
pins are also bidirectional. Regardless of interface width,
DDR3 SDRAM interfaces can operate in either ×4 or ×8 mode DQS groups, which is
dependent on your chosen memory device or DIMM. The ×4 and ×8 configurations
use one pair of bidirectional data strobe signals,
DQS
and
DQS#
, to capture input data.
However, two pairs of data strobes,
UDQS
and
UDQS#
(upper byte), and
LDQS
and
LDQS#
(lower byte), are required by the ×16 configuration devices. A group of
DQ
pins
must remain associated with its respective
DQS
and
DQS#
pins.
The
DQ
signals are edge-aligned with the
DQS
signal during a read from the memory
and are center-aligned with the
DQS
signal during a write to the memory. The PHY
shifts the
DQ
signals by –90
°
during a write operation to center align the
DQ
and
DQS
signals. The memory controller delays the
DQS
signal during a read, so that the
DQ
and
DQS
signals are center aligned at the capture register. Stratix III devices use a
phase-locked loop (PLL) to center-align the
DQS
signal with respect to the
DQ
signals
during writes and use DLL-controlled DQS phase-shift circuitry to shift the incoming
DQS
signal during reads.