MT48LC4M4A1 Datasheet, PDF (11/50 Pages) Micron Technology – SYNCHRONOUS DRAM

COMMAND INHIBIT
The COMMAND INHIBIT function prevents new com-
mands from being executed by the SDRAM, regardless of
whether the CLK signal is enabled. The SDRAM is effec-
tively deactivated, or deselected.
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.
LOAD MODE REGISTER
The Mode Register is loaded via inputs A0-A10 and
BA. See Mode Register heading in Register Definition
section. The LOAD MODE REGISTER command can only
be issued when both banks are idle, and a subsequent
executable 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 BA input selects the bank, and the address
provided on inputs A0-A10 selects the row. This row
remains active (or open) for accesses until a PRECHARGE
command is issued to that bank. A PRECHARGE com-
mand must be issued before opening a different row in
the same bank.
READ
The READ command is used to initiate a burst read
access to an active row. The value on the BA input selects
the bank, and the address provided on inputs A0-A9 (A9
is a “Don’t Care” on x8) 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 selected, the row
will remain open for subsequent accesses. Read data
appears on the DQs, subject to the logic level on the DQM
input, two clocks earlier. If the DQM signal was regis-
tered HIGH, the DQs will be High-Z two clocks later; if the
DQM signal was registered LOW, the DQs will provide
valid data.
WRITE
The WRITE command is used to initiate a burst write
access to an active row. The value on the BA input selects
the bank, and the address provided on inputs A0-A9 (A9
is a “Don’t Care” on x8) selects the starting column
location. The value on input A10 determines whether or
not auto precharge is used. If auto precharge is selected,
16 MEG: x4, x8
SDRAM
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 accesses. Input
data appearing on the DQs is written to the memory array
subject to the DQM input logic level appearing coinci-
dent with the data. If the DQM signal is registered LOW,
the corresponding data will be written to memory; if the
DQM signal is registered HIGH, the corresponding data
inputs will be ignored, and a WRITE will not be executed
to that location.
PRECHARGE
The PRECHARGE command is used to deactivate the
open row in a particular bank or the open row in both
banks. The bank(s) will be available for a subsequent row
access some specified time (^tRP) after the PRECHARGE
command is issued. Input A10 determines whether one
or both banks are to be precharged, and in the case where
only one bank is to be precharged, input BA selects the
bank. Otherwise BA is treated as a “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.
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 initi-
ated at the earliest valid stage within a burst. The user
must not issue another command until the precharge
time (^tRP) is completed. This is determined as if an ex-
plicit PRECHARGE command was issued at the earliest
possible time, as described for each burst type in the
Operation section of this data sheet.
BURST TERMINATE
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.
16 Meg: x4, x8 SDRAM
16MSDRAMx4x8_B.p65 – Rev. 5/98
11
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©1998, Micron Technology, Inc.