W9725G6KB25I-TR Datasheet, PDF (23/87 Pages) Winbond – 4M X 4 BANKS X 16 BIT DDR2 SDRAM

W9725G6KB
8.3.10 No-Operation Command
( CS = "L", RAS = "H", CAS = "H", WE = "H", CKE, BA0, BA1, A0 to A12 = Don‟t Care)
The No-Operation command simply performs no operation (same command as Device Deselect).
8.3.11 Device Deselect Command
( CS = "H", RAS , CAS , WE , CKE, BA0, BA1, A0 to A12 = Don‟t Care)
The Device Deselect command disables the command decoder so that the RAS , CAS , WE and
Address inputs are ignored. This command is similar to the No-Operation command.
8.4 Read and Write access modes
The DDR2 SDRAM provides a fast column access operation. A single Read or Write Command will
initiate a serial read or write operation on successive clock cycles. The boundary of the burst cycle is
strictly restricted to specific segments of the page length.
The 4 Mbit x 16 I/O x 4 Bank chip has a page length of 512 bits (defined by CA0 to CA8)^*. The page
length of 512 is divided into 128 or 64 uniquely addressable boundary segments depending on burst
length, 128 for 4 bit burst, 64 for 8 bit burst respectively. A 4-bit or 8-bit burst operation will occur
entirely within one of the 128 or 64 groups beginning with the column address supplied to the device
during the Read or Write Command (CA0 to CA8). The second, third and fourth access will also occur
within this group segment. However, the burst order is a function of the starting address, and the burst
sequence.
A new burst access must not interrupt the previous 4 bit burst operation in case of BL = 4 setting.
However, in case of BL = 8 setting, two cases of interrupt by a new burst access are allowed, one
reads interrupted by a read, the other writes interrupted by a write with 4 bit burst boundary
respectively. The minimum CAS to CAS delay is defined by tCCD, and is a minimum of 2 clocks for
read or write cycles.
Note: Page length is a function of I/O organization and column addressing
4M bits × 16 organization (CA0 to CA8); Page Length = 512 bits
8.4.1 Posted CAS
Posted CAS operation is supported to make command and data bus efficient for sustainable
bandwidths in DDR2 SDRAM. In this operation, the DDR2 SDRAM allows a CAS read or write
command to be issued immediately after the RAS bank activate command (or any time during the
RAS - CAS -delay time, tRCD, period). The command is held for the time of the Additive Latency (AL)
before it is issued inside the device. The Read Latency (RL) is controlled by the sum of AL and the
CAS Latency (CL). Therefore if a user chooses to issue a Read/Write command before the tRCDmin,
then AL (greater than 0) must be written into the EMR (1). The Write Latency (WL) is always defined
as RL -1 (Read Latency -1) where Read Latency is defined as the sum of Additive Latency plus CAS
Latency (RL = AL + CL). Read or Write operations using AL allow seamless bursts. (Example timing
waveforms refer to 11.10 and 11.11 seamless burst read/write operation diagram in Chapter 11)
8.4.1.1 Examples of posted CAS operation
Examples of a read followed by a write to the same bank where AL = 2 and where AL = 0 are shown
in Figures 14 and 15, respectively.
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Publication Release Date: Sep. 03, 2012
Revision A03