IBM0625404GT3B IBM0625164GT3B
IBM0625804GT3B IBM06254B4GT3B
256Mb Double Data Rate Synchronous DRAM
Advance
Deselect
The Deselect function prevents new commands from being executed by the DDR SDRAM. The DDR SDRAM
is effectively deselected. Operations already in progress are not affected.
No Operation (NOP)
The No Operation (NOP) command is used to perform a NOP to a DDR SDRAM. This prevents unwanted
commands from being registered during idle or wait states. Operations already in progress are not affected.
Mode Register Set
The mode registers are loaded via inputs A0-A12, BA0 and BA1. See mode register descriptions in the Reg-
ister Definition section. The Mode Register Set command can only be issued when all banks are idle and no
bursts are in progress. A subsequent executable command cannot be issued until t
is met.
MRD
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 (or Read or Write with Auto Precharge) is
issued to that bank. A Precharge (or Read or Write with Auto Precharge) command must be issued and com-
pleted before opening a different row in the same bank.
Read
The Read command is used to initiate a burst read access to an active (open) row. The value on the BA0,
BA1 inputs selects the bank, and the address provided on inputs A0-Ai, Aj (where [i = 9, j = don’t care] for x8;
where [i = 9, j = 11] for x4) 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 is precharged at the end
of the Read burst; if Auto Precharge is not selected, the row remains open for subsequent accesses.
Write
The Write command is used to initiate a burst write access to an active (open) row. The value on the BA0,
BA1 inputs selects the bank, and the address provided on inputs A0-Ai, Aj (where [i = 9, j = don’t care] for x8;
where [i = 9, j = 11] for x4) 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 is precharged at the end
of the Write burst; if Auto Precharge is not selected, the row remains open for subsequent accesses. Input
data appearing on the DQs is written to the memory array subject to the DM input logic level appearing coin-
cident with the data. If a given DM signal is registered low, the corresponding data is written to memory; if the
DM signal is registered high, the corresponding data inputs are ignored, and a Write is not executed to that
byte/column location.
Precharge
The Precharge command is used to deactivate (close) the open row in a particular bank or the open row(s) in
all banks. The bank(s) will be available for a subsequent row access a specified time (t ) after the Pre-
RP
charge command is issued. Input A10 determines whether one or all banks are to be precharged, and in the
case where only one bank 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. A precharge command is treated as a NOP if
there is no open row in that bank, or if the previously open row is already in the process of precharging.
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Use is further subject to the provisions at the end of this document.
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