General Description
DDR2 SDRAM modules are high-speed, CMOS dynamic random access memory mod-
ules that use internally configured 4 or 8-bank DDR2 SDRAM devices. DDR2 SDRAM
modules use DDR architecture to achieve high-speed operation. DDR2 architecture is
essentially a 4n-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 DDR2 SDRAM
module effectively consists of a single 4n-bit-wide, one-clock-cycle data transfer at the
internal DRAM core and eight corresponding n-bit-wide, one-half-clock-cycle data trans-
fers at the I/O pins.
DDR2 modules use two sets of differential signals: DQS, DQS# to capture data and CK
and CK# to capture commands, addresses, and control signals. Differential clocks and
data strobes ensure exceptional noise immunity for these signals and provide precise
crossing points to capture input signals. A bidirectional data strobe (DQS, DQS#) is trans-
mitted externally, along with data, for use in data capture at the receiver. DQS is a
strobe transmitted by the DDR2 SDRAM device during READs and by the memory con-
troller during WRITEs. DQS is edge-aligned with data for READs and center-aligned
with data for WRITEs.
DDR2 SDRAM modules operate from a differential clock (CK and CK#); the crossing of
CK going HIGH and CK# going LOW will be referred to as the positive edge of CK. Com-
mands (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.
Serial Presence-Detect EEPROM Operation
DDR2 SDRAM modules incorporate serial presence-detect. The SPD data is stored in a
256-byte EEPROM. The first 128 bytes are programmed by Micron to identify the mod-
ule type and various SDRAM organizations and timing parameters. The remaining 128
bytes of storage are available for use by the customer. System READ/WRITE operations
between the master (system logic) and the slave EEPROM device occur via a standard
I
2
C bus using the DIMM’s SCL (clock) SDA (data), and SA (address) pins. Write protect
(WP) is connected to V
SS
, permanently disabling hardware write protection.
Register and PLL Operation
DDR2 SDRAM modules operate in registered mode, where the command/address input
signals are latched in the registers on the rising clock edge and sent to the DDR2
SDRAM devices on the following rising clock edge (data access is delayed by one clock
cycle). A phase-lock loop (PLL) on the module receives and redrives the differential
clock signals (CK, CK#) to the DDR2 SDRAM devices. The registers and PLL minimize
system and clock loading. PLL clock timing is defined by JEDEC specifications and en-
sured by use of the JEDEC clock reference board. Registered mode will add one clock
cycle to CL.
Parity Operations
The registering clock driver can accept a parity bit from the system’s memory control-
ler, providing even parity for the control, command, and address bus. Parity errors are
flagged on the Err_Out# pin. Systems not using parity are expected to function without
issue if Par_In and Err_Out# are left as no connects (NC) to the system.
1GB, 2GB, 4GB (x72, ECC, DR) 240-Pin DDR2 SDRAM RDIMM
General Description
PDF: 09005aef83d3d893
htf18c128_256_512x72pdz.pdf - Rev. D 11/10 EN
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Micron Technology, Inc. reserves the right to change products or specifications without notice.
© 2009 Micron Technology, Inc. All rights reserved.
