128Mb: x4, x8, x16
SDRAM
COMMAND INHIBIT
whether or not auto precharge is used. If auto precharge
is selected, the row being accessed will be precharged at
the end of the WRITE burst; if auto precharge is not
selected, the row will remain open for subsequent ac-
cesses. Input data appearing on the DQs is written to the
memory array subject to the DQM input logic level ap-
pearing coincident with the data. If a given DQM signal is
registeredLOW, thecorrespondingdatawillbewrittento
memory; if the DQM signal is registered HIGH, the corre-
sponding data inputs will be ignored, and a WRITE will
not be executed to that byte/column location.
TheCOMMANDINHIBITfunctionpreventsnewcom-
mands from being executed by the SDRAM, regardless of
whether the CLK signal is enabled. The SDRAM is effec-
tively deselected. Operations already in progress are not
affected.
NO OPERATION (NOP)
The NO OPERATION (NOP) command is used to per-
form a NOP to an SDRAM which is selected (CS# is LOW).
This prevents unwanted commands from being regis-
tered during idle or wait states. Operations already in
progress are not affected.
PRECHARGE
The PRECHARGE command is used to deactivate the
openrowinaparticularbankortheopenrowinallbanks.
The bank(s) will be available for a subsequent row access
a specified time (tRP) after the PRECHARGE command is
issued. Input A10 determines whether one or all banks
aretobeprecharged, andinthecasewhereonlyonebank
is to be precharged, inputs BA0, BA1 select the bank.
Otherwise BA0, BA1 are treated as “Don’t Care.” Once a
bank has been precharged, it is in the idle state and must
be activated prior to any READ or WRITE commands
being issued to that bank.
LOAD MODE REGISTER
The mode register is loaded via inputs A0-A11. See
mode register heading in the Register Definition section.
The LOAD MODE REGISTER command can only be is-
sued when all banks are idle, and a subsequent execut-
able command cannot be issued until tMRD is met.
ACTIVE
The ACTIVE command is used to open (or activate) a
row in a particular bank for a subsequent access. The
value on the BA0, BA1 inputs selects the bank, and the
address provided on inputs A0-A11 selects the row. This
row remains active (or open) for accesses until a
PRECHARGE command is issued to that bank. A
PRECHARGE command must be issued before opening a
different row in the same bank.
AUTO PRECHARGE
Auto precharge is a feature which performs the same
individual-bank PRECHARGE function described above,
without requiring an explicit command. This is accom-
plished by using A10 to enable auto precharge in con-
junction 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, except in
the full-page burst mode, where auto precharge does not
apply. Auto precharge is nonpersistent in that it is either
enabled or disabled for each individual READ or WRITE
command.
Auto precharge ensures that the precharge is initiated
at the earliest valid stage within a burst. The user must
not issue another command to the same bank until the
precharge time (tRP) is completed. This is determined as
if an explicit PRECHARGE command was issued at the
earliest possible time, as described for each burst type in
the Operation section of this data sheet.
READ
The READ command is used to initiate a burst read
access to an active row. The value on the BA0, BA1 inputs
selects the bank, and the address provided on inputs A0-
A9, A11 (x4), A0-A9 (x8) or A0-A8 (x16) selects the starting
column location. The value on input A10 determines
whether or not auto precharge is used. If auto precharge
is selected, the row being accessed will be precharged at
the end of the READ burst; if auto precharge is not se-
lected, therowwillremainopenforsubsequentaccesses.
Read data appears on the DQs subject to the logic level on
the DQM inputs two clocks earlier. If a given DQM signal
was registered HIGH, the corresponding DQs will be
High-Z two clocks later; if the DQM signal was registered
LOW, the DQs will provide valid data.
BURST TERMINATE
WRITE
The BURST TERMINATE command is used to trun-
cate either fixed-length or full-page bursts. The most
recently registered READ or WRITE command prior to
the BURST TERMINATE command will be truncated, as
shown in the Operation section of this data sheet.
The WRITE command is used to initiate a burst write
access to an active row. The value on the BA0, BA1 inputs
selects the bank, and the address provided on inputs A0-
A9, A11 (x4), A0-A9 (x8) or A0-A8 (x16) selects the starting
column location. The value on input A10 determines
128Mb: x4, x8, x16 SDRAM
128MSDRAM_E.p65 – Rev. E; Pub. 1/02
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©2001, Micron Technology, Inc.
13
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