EMD56324P Datasheet, PDF (20/45 Pages) Emerging Memory & Logic Solutions Inc – 256M: 8M x 32 Mobile DDR SDRAM

Preliminary
EMD56324P
256M: 8M x 32 Mobile DDR SDRAM
AUTO PRECHARGE
AUTO PRECHARGE is a feature which performs the same individual-bank precharge function described above, but
without requiring an explicit command. This is accomplished by using A10 to enable auto precharge in conjunction with
a specific READ or WRITE command. A precharge of the bank/row that is addressed with the READ or WRITE com-
mand is automatically performed upon completion of the READ or WRITE burst. Auto precharge is nonpersistent in
that it is either enabled or disabled for each individual READ or WRITE command. This device supports concurrent
auto precharge if the command to the other bank does not interrupt the data transfer to the current bank.
AUTO PRECHARGE ensures that the precharge is initiated at the earliest valid stage within a burst. This “earliest valid
stage” is determined as if an explicit PRECHARGE command was issued at the earliest possible time, without violating
tRAS (MIN), as described for each burst type in “Operations”. The user must not issue another command to the same
bank until the precharge time (tRP) is completed.
BURST TERMINATE
The BURST TERMINATE command is used to truncate READ bursts (with auto precharge disabled). The most
recently registered READ command prior to the BURST TERMINATE command will be truncated, as shown in “Oper-
ations”. The open page which the READ burst was terminated from remains open.
AUTO REFRESH
AUTO REFRESH is used during normal operation of the Mobile DDR SDRAM and is analogous to CAS-BEFORE-
RAS (CBR) REFRESH in FPM/EDO DRAMs. This command is nonpersistent, so it must be issued each time a refresh
is required.
The addressing is generated by the internal refresh controller. This makes the address bits a “Don’t Care” during an
AUTO REFRESH command. The 256Mb Mobile DDR SDRAM requires AUTO REFRESH cycles at an average inter-
val of 15.625µs (maximum).
To allow for improved efficiency in scheduling and switching between tasks, some flexibility in the absolute refresh
interval is provided. Although not a JEDEC requirement, to provide for future functionality features, CKE must be
active (HIGH) during the auto refresh period. The auto refresh period begins when the AUTO REFRESH command is
registered and ends tRFC later.
Auto Refresh
CKB
CK
Command
PRE
Auto
Refresh
CMD
CKE = High
tRP
tRFC
20
Rev 0.0