HYB25D256[400/800/160]B[T/C](L)
256-Mbit Double Data Rate SDRAM
Functional Description
3.4
Commands
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 Register
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 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-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 completed 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 = 8, j = don’t care] for × 16, [i = 9,
j = don’t care] for × 8 and [i = 9, j = 11] for × 4) 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 × 8; where
[i = 9, j = 11] for × 4) 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 coincident 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 (tRP) after the Precharge
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.
Data Sheet
21
Rev. 1.21, 2004-07
02102004-TSR1-4ZWW
QIMONDA [ QIMONDA AG ]
