Table 6. Commands
13. CKE is HIGH for all commands shown except SELF REFRESH and Deep Power Down.
14. A0-A11 provide row address, and BA determine which bank is made active.
15. A0-A7 provide column address; A10 HIGH enables the auto precharge feature (nonpersistent), while A10 LOW disables the auto precharge feature; BA determine which
bank is being read from or written to.
16. A10 LOW: BA determine the bank being precharged. A10 HIGH: All banks precharged and BA are “Don’t Care.”
17. Internal refresh counter controls row addressing; all inputs and I/Os are “Don’t Care” except for CKE.
18. This command is AUTO REFRESH if CKEn is HIGH, SELF REFRESH if CKEn is LOW.
19. A0-A9 define the op-code written to the mode register and BA determine Normal MRS and Extended MRS.
20. Activates or deactivates the DQs during WRITEs (zero-clock delay) and READs (two-clock delay). LDQM controls DQ0-7, UDQM1controls DQ8-15
Table 6. provides a reference of all the commands available
with the state of the control signals for executing a specific
The COMMAND INHIBIT function effectively deselects the
SDRAM by preventing new commands from being executed by
the SDRAM, regardless of whether the CLK signal is enabled.
Operations already in progress are not affected.
LOAD MODE REGISTER
The mode register is loaded via inputs A0-A10, BA. The
LOAD MODE REGISTER and LOAD EXTENDED MODE
REGISTER commands can only be issued wh e n all
banks are idle, and a subsequent executable command cannot
be issued until t
is met. Table 1. and Table 4. provide the
definition for the Mode Register and Extended Mode Register.
NO OPERATION (NOP)
The NO OPERATION (NOP) command is used to perform a
NOP to an SDRAM which is selected (/CS is LOW). This pre-
vents unwanted commands from being registered during idle
or wait states. Operations already in progress are not affected.
The ACTIVE command is used to activate a row in a particular
bank for a subsequent access. The value on the BA inputs
selects the bank, and the address provided on inputs
A0-A10 selects the row. This row remains active 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.
READ command is used to initiate a burst read access to an
active row. The value on the BA inputs selects the bank,
and the address provided on inputs A0-A7 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 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.
Rev0.3, May., 2010
The WRITE command is used to initiate a burst write access
to an active row. The value on the BA inputs selects the
bank, and the address provided on inputs A0-A7 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 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 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 registered HIGH, the
corresponding data inputs will be ignored, and a WRITE will not
be executed to that byte/column location.
The PRECHARGE command is used to deactivate the active
row in a particular bank or the active row in all banks. The
bank(s) will be available for a subsequent row access a spec-
ified time (t
) after the PRECHARGE command is issued.
Input A10 determines whether one or all banks are to be pre-
charged, and in the case where only one bank is to be pre-
charged, inputs BA select the bank. Otherwise BA is treated as
“Don’t Care.” Once a bank has been pre-charged, it is in the
idle state and must be activated prior to any READ or WRITE
commands being issued to that bank.
AUTO PRECHARGE is accomplished by using A10 to enable
auto precharge in conjunction with a specific READ or WRITE
command. AUTO PRECHARGE thus performs the same
PRECHARGE command described above , without requiring an
explicit 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.
AUTO PRECHARGE does not apply in the full page mode burst.
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
) is completed.
The BURST TERMINATE command is used to truncate either
fixed-length or full-page bursts. The most recently registered
READ or WRITE command prior to the BURST TERMINATE
command will be truncated.