Functional Description

The DDR 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 DDR SDRAM effectively consists of a single 2n-bit-wide, one-clockcycle data transfer at the internal DRAM core and two corresponding n-bit-wide, onehalf-clock-cycle data transfers at the I/O pins.

特性 Features

? VDD = +2.5V ±0.2V, VDDQ = +2.5V ±0.2V

? VDD = +2.6V ±0.1V, VDDQ = +2.6V ±0.1V (DDR400)

? Bidirectional data strobe (DQS) transmitted/

received with data, i.e., source-synchronous data

capture (x16 has two – one per byte)

? Internal, pipelined double-data-rate (DDR)

architecture; two data accesses per clock cycle

? Differential clock inputs (CK and CK#)

? Commands entered on each positive CK edge

? DQS edge-aligned with data for READs; centeraligned with data for WRITEs

? DLL to align DQ and DQS transitions with CK

? Four internal banks for concurrent operation

? Data mask (DM) for masking write data

(x16 has two – one per byte)

? Programmable burst lengths: 2, 4, or 8

? Auto refresh

– 64ms, 8192-cycle(Commercial and industrial)

– 16ms, 8192-cycle (Automotive)

? Self refresh (not available on AT devices)

? Longer-lead TSOP for improved reliability (OCPL)

? 2.5V I/O (SSTL_2 compatible)

? Concurrent auto precharge option is supported

? tRAS lockout supported (tRAP = tRCD)