EtronTech
DM Masking Function
EM68932DVKB
The DDR SDRAM has a Data Mask function that can be used in conjunction with the data write cycle only,
not the read cycle. When the Data Mask is activated (DM High) during a write operation, the write data is
masked immediately (DM to Data Mask latency is zero). DM must be issued at the rising edge or the falling
edge of Data Strobe instead of at a clock edge.
Auto Precharge Operation
Auto Precharge is a feature which performs the same individual bank precharge function as described
above, but without requiring an explicit command. This is accomplished by using A10 (A10 = High), 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 command is automatically performed upon completion of
the read or write burst. Auto Precharge is non persistent in that it is either enabled or disabled for each
individual READ or WRITE command. Auto Precharge ensures that a precharge is initiated at the earliest
valid stage within a burst. The user must not issue another command to the same bank until the
precharging time (t
RP
) is completed. When the Auto Precharge command is activated, the active bank
automatically begins to precharge at the earliest possible moment during a read or write cycle after t
RAS
(min) is satisfied.
Precharge Command
The Precharge command is issued when
CS
,
RAS
, and
WE
are Low and
CAS
is High at the rising edge
of the clock (CK). The Precharge command can be used to precharge any bank individually or all banks
simultaneously. The Bank Select addresses (BA0, BA1) are used to define which bank is precharged when
the command is initiated. For a write cycle, t
WR
(min) must be satisfied from the start of the last Burst Write
cycle until the Precharge command can be issued. After t
RP
from the precharge, an Active command to the
same bank can be initiated.
Auto Refresh
An Auto Refresh command is issued by having
CS
,
RAS
, and
CAS
held Low with CKE and
WE
High at
the rising edge of the clock (CK). All banks must be precharged and idle for a tRP (min) before the Auto
Refresh command is applied. The refresh addressing is generated by the internal refresh address counter.
This makes the address bits
“
Don’t Care
＂
during an Auto Refresh command. When the refresh cycle is
complete, all banks will be in the idle state. A delay between the Auto Refresh command and the next
Active command or subsequent Auto Refresh command must be greater than or equal to the t
RFC
(min).
Self Refresh
A Self Refresh command is defined by having
CS
,
RAS
,
CAS
and CKE Low with
WE
High at the rising
edge of the clock (CK). Once the Self Refresh command has been initiated, CKE must be held Low to keep
the device in Self Refresh mode. During the Self Refresh operation, all inputs except CKE are ignored. The
clock is internally disabled during Self Refresh operation to reduce power consumption. To exit the Self
Refresh mode, supply a stable clock input before returning CKE high, assert Deselect or a NOP command,
and then assert CKE high.
Power Down Mode
The device enters Power Down mode when CKE is brought Low, and it exits when CKE returns High. Once
the Power Down mode is initiated, all of the receiver circuits except CK and CKE are gated off to reduce
power consumption. All banks should be in an idle state prior to entering the Precharge Power Down mode
and CKE should be set high at least t
XP
prior to an Active command. During Power Down mode, refresh
operations cannot be performed; therefore the device must remain in Power Down mode for a shorter time
than the refresh period (t
REF
) of the device.
Etron Confidential
12
Rev. 1.0
Aug. 2009
ETRON [ ETRON TECHNOLOGY, INC. ]
