AS4SD16M72PBG-s/IT,ET,XT
16M x 72, SDR SDRAM, 3.3v Core/ 3.3v IO
Load Mode Register
The MODE REGISTER is loaded via inputs A0-A11 (A12
should be driven LOW). See MODE REGISTER heading in
the REGISTER DEFINITION section. The LOAD MODE
REGISTER command can only be issued when all banks are
idle, and a subsequent executable command cannot be issued
until tMRD is met.
HIGH, the corresponding data inputs will be ignored, and
a WRITE will not be executed to that byte/column
location.
Precharge
The PRECHARGE command is used to deactivate the
open row in a particular bank or the open row in all
banks. 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 are 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.
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-A12 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
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 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 Operation.
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-A8 (each 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 will remain open
for subsequent accesses. 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.
Write
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-A8
(each 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 WRITE
BURST; if for subsequent accesses input data appearing on
the DQs is WRITTEN to the memory array subject to the
DQM input logic level appearing coincident with the data. If
a given DQM signal is registered LOW, the corresponding
data will be written to memory; if the DQM signal is
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Burst Terminate
The BURST TERMINATE command is used to truncate
either a fixed-length or full-page burst. The most recently
registered READ or WRITE command prior to the
BURST TERMINATE command will be truncated.
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