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Micron Technology, Inc., reserves the right to change products or specifications without notice.
HVF18C64_128_256x72G_2.fm - Rev. A 8/05 EN
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2003 Micron Technology, Inc. All rights reserved.
512MB, 1GB, 2GB: (x72, SR) 240-Pin DDR2 VLP RDIMM
General Description
The MT18HVF6472(P), MT18HVF12872(P), and MT18HVF25672(P) DDR2 SDRAM mod-
ules are high-speed, CMOS, dynamic random-access 512MB, 1GB, and 2GB memory
modules organized in x72 configuration. DDR2 SDRAM modules use internally config-
ured 4-bank (512MB, 1GB) or 8-bank (2GB) DDR2 SDRAM devices.
DDR2 SDRAM modules use double data rate architecture to achieve high-speed opera-
tion. The double data rate 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 four corresponding
n-bit-wide, one-half-clock-cycle data transfers at the I/O pins.
A bidirectional data strobe (DQS, DQS#) is transmitted 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 controller 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.
Read and write accesses to DDR2 SDRAM modules 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 device bank and row to be accessed. The
address bits registered coincident with the READ or WRITE command are used to select
the device bank and the starting column location for the burst access.
DDR2 SDRAM modules provide for programmable read or write burst lengths of four or
eight locations. DDR2 SDRAM devices support interrupting a burst read of eight with
another read, or a burst write of eight with another write. An auto precharge function
may be enabled to provide a self-timed row precharge that is initiated at the end of the
burst access.
The pipelined, multibank architecture of DDR2 SDRAM devices allows for concurrent
operation, thereby providing high, effective bandwidth by hiding row precharge and
activation time.
A self refresh mode is provided, along with a power-saving power-down mode.
All inputs are compatible with the JEDEC standard for SSTL_18. All full drive-strength
outputs are SSTL_18-compatible.
PLL and Register 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. Registered mode will add one clock cycle to CL.