Internet Data Sheet
HY[B/I]25D256[16/40/80]0C[E/C/F/T](L)
256 Mbit Double-Data-Rate SDRAM
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Functional Description
The 256 Mbit Double-Data-Rate SDRAM is a high-speed CMOS, dynamic random-access memory containing
268,435,456 bits. The 256 Mbit Double-Data-Rate SDRAM is internally configured as a quad-bank DRAM.
The 256 Mbit Double-Data-Rate SDRAM uses a double-data-rate architecture 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 256 Mbit Double-Data-Rate SDRAM 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.
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 (BA0, BA1 select the bank; A0-A12 select the row). The address bits registered
coincident with the Read or Write command are used to select the starting column location for the burst access.
Prior to normal operation, the DDR SDRAM must be initialized. The following sections provide detailed information covering
device initialization, register definition, command descriptions and device operation.
Rev. 2.3, 2007-03
03062006-8CCM-VPUW
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QIMONDA [ QIMONDA AG ]
