DEVICE OVERVIEW
ISSI’s 256-Mbit DDR SDRAM achieves high speed data transfer using pipeline architecture and two data word accesses per clock cycle. The 268,435,456-bit memory array is internally organized as four banks of 64Mb to allow concurrent operations. The pipeline allows Read and Write burst accesses to be virtually continuous, with the option to concatenate or truncate the bursts. The programmable features of burst length, burst sequence and CAS latency enable further advantages. 

FEATURES
• VDD and VDDQ: 2.5V ± 0.2V
• SSTL_2 compatible I/O
• Double-data rate architecture; two data transfers
   per clock cycle
• Bidirectional, data strobe (DQS) is transmitted/
   received with data, to be used in capturing data
   at the receiver
• DQS is edge-aligned with data for READs and
   centre-aligned with data for WRITEs
• Differential clock inputs (CK and CK)
• DLL aligns DQ and DQS transitions with CK
   transitions
• Commands entered on each positive CK edge; data
   and data mask referenced to both edges of DQS
• Four internal banks for concurrent operation
• Data Mask for write data. DM masks write data
   at both rising and falling edges of data strobe
• Burst Length: 2, 4 and 8
• Burst Type: Sequential and Interleave mode
• Programmable CAS latency: 2, 2.5 and 3
• Auto Refresh and Self Refresh Modes
• Auto Precharge
• TRAS Lockout supported (tRAP = tRCD)