![](http://datasheet.mmic.net.cn/180000/MT47H128M8HV-187ELIT-E_datasheet_11334050/MT47H128M8HV-187ELIT-E_74.png)
NO OPERATION (NOP)
The NO OPERATION (NOP) command is used to instruct the selected DDR2 SDRAM to
perform a NOP (CS# is LOW; RAS#, CAS#, and WE are HIGH). This prevents unwanted
commands from being registered during idle or wait states. Operations already in pro-
gress are not affected.
LOAD MODE (LM)
The mode registers are loaded via bank address and address inputs. The bank address
(page 75). The LM command can only be issued when all banks are idle, and a subse-
quent executable command cannot be issued until tMRD is met.
ACTIVATE
The ACTIVATE command is used to open (or activate) a row in a particular bank for a
subsequent access. The value on the bank address inputs determines the bank, and the
address inputs select the row. This row remains active (or open) for accesses until a pre-
charge command is issued to that bank. A precharge command 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 bank address inputs determine the bank, and the address provided on address
inputs A0–Ai (where Ai is the most significant column address bit for a given configura-
tion) 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.
DDR2 SDRAM also supports the AL feature, which allows a READ or WRITE command
to be issued prior to tRCD (MIN) by delaying the actual registration of the READ/WRITE
command to the internal device by AL clock cycles.
WRITE
The WRITE command is used to initiate a burst write access to an active row. The value
on the bank select inputs selects the bank, and the address provided on inputs A0–Ai
(where Ai is the most significant column address bit for a given configuration) 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 pre-
charged at the end of the WRITE burst; if auto precharge is not selected, the row will
remain open for subsequent accesses.
DDR2 SDRAM also supports the AL feature, which allows a READ or WRITE command
to be issued prior to tRCD (MIN) by delaying the actual registration of the READ/WRITE
command to the internal device by AL clock cycles.
Input data appearing on the DQ 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 will be written to memory; if the DM signal is registered HIGH,
the corresponding data inputs will be ignored, and a WRITE will not be executed to that
1Gb: x4, x8, x16 DDR2 SDRAM
Commands
PDF: 09005aef821ae8bf
1GbDDR2.pdf – Rev. S 10/09 EN
74
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