HY5PS1G821M Datasheet, PDF (26/79 Pages) Hynix Semiconductor – 1Gb DDR2 SDRAM(DDP)

1HY5PS12421(L)M
HY5PS12821(L)M
2.5 Read and Write Access Modes
After a bank has been activated, a read or write cycle can be executed. This is accomplished by setting RAS
high, CS and CAS low at the clock’s rising edge. WE must also be defined at this time to determine whether
the access cycle is a read operation (WE high) or a write operation (WE low).
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. For example, the 32Mbit x 4 I/O x 4 Bank chip has a page length of
2048 bits (defined by CA0-CA9, CA11). The page length of 2048 is divided into 512 or 256 uniquely addres-
sable boundary segments depending on burst length, 512 for 4 bit burst, 256 for 8 bit burst respectively. A 4-
bit or 8 bit burst operation will occur entirely within one of the 512 or 256 groups beginning with the column
address supplied to the device during the Read or Write Command (CA0-CA9, CA11). 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 boundry respectively. The minimum CAS to
CAS delay is defined by tCCD, and is a minimum of 2 clocks for read or write cycles.
Rev. 0.2 / Oct. 2005
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