CMS4A16LAx–75Ex
Note :
13. CKE is HIGH for all commands shown except SELF REFRESH and Deep Power Down.
14. A0-A11 provide row address, and BA0, BA1 determine which bank is made active.
15. A0-A8 provide column address; A10 HIGH enables the auto precharge feature (nonpersistent), while A10 LOW disables the auto precharge feature; BA0, BA1 determine which
bank is being read from or written to.
16. A10 LOW: BA0, BA1 determine the bank being precharged. A10 HIGH: All banks precharged and BA0, BA1 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 CKE is HIGH, SELF REFRESH if CKE is LOW.
19. A0-A9 define the op-code written to the mode register and BA0, BA1 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 and UDQM controls DQ8-15.
WRITE
Commands
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 selects the
with the state of the control signals for executing a specific
Table 6. provides a reference of all the commands available
starting column location. The value on input A10 determines
whether or not auto precharge is used. If auto precharge is
command.
selected, the row being accessed will be precharged at the end
COMMAND INHIBIT
of the WRITE burst. If auto precharge is not selected, the row
The COMMAND INHIBIT function effectively deselects the
will remain open for subsequent accesses. Input data appearing
SDRAM by preventing new commands from being executed by
on the DQs is written to the memory array subject to the DQM
the SDRAM, regardless of whether the CLK signal is enabled.
input logic level appearing coincident with the data. If a given
Operations already in progress are not affected.
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
The NO OPERATION (NOP) command is used to perform a
be executed to that byte/column location.
NO OPERATION (NOP)
NOP to an SDRAM which is selected (/CS is LOW). This pre-
vents unwanted commands from being registered during idle
PRECHARGE
or wait states. Operations already in progress are not affected.
The PRECHARGE command is used to deactivate the active
row in a particular bank or the active row in all banks. The
LOAD MODE REGISTER
bank(s) will be available for a subsequent row access after a
The mode register is loaded via inputs A0-A11, BA0, BA1.
specified time (tRP) from the issued PRECHARGE command.
The LOAD MODE REGISTER and LOAD EXTENDED
Input A10 determines whether one or all banks are to be pre-
MODE REGISTER commands can only be issued when all
charged, and in the case where only one bank is to be pre-
banks are idle, and a subsequent executable command cannot
charged, inputs BA0, BA1 select the bank. Otherwise BA0,
be issued until tMRD is met. Table 1, Table 4 And Table 5
BA1 are treated as “Don’t Care.” Once a bank has been pre-
provide the definition for the Mode Register and Extended
charged, it is in the idle state and must be activated prior to
Mode Register.
any READ or WRITE commands being issued to that bank.
ACTIVE
AUTO PRECHARGE
The ACTIVE command is used to activate a row in a particular
AUTO PRECHARGE is accomplished by using A10 to enable
bank for a subsequent access. The value on the BA0, BA1
auto precharge in conjunction with a specific READ or WRITE
inputs selects the bank, and the address provided on inputs
command. AUTO PRECHARGE thus performs the same
A0-A11 selects the row. This row remains active for accesses
PRECHARGE command described above , without requiring an
until a PRECHARGE command is issued to that bank. A
explicit command. A PRECHARGE of the bank/row that is
PRECHARGE command must be issued before opening a
addressed with the READ or WRITE command is automatically
different row in the same bank.
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
READ
READ command is used to initiate a burst read access to an
disabled for each individual READ or WRITE command.
active row. The value on the BA0, BA1 inputs selects the bank,
Auto precharge ensures that the precharge is initiated at the
and the address provided on inputs A0-A8 selects the starting
earliest valid stage within a burst. The user must not issue
column location. The value on input A10 determines whether or
another command to the same bank until the precharge time
not auto precharge is used. If auto precharge is selected, the
row being accessed will be precharged at the end of the READ
(tRP) is completed.
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
fixed-length or full-page bursts. The most recently registered
a given DQM signal was registered HIGH, the corresponding
DQs will be High-Z two clocks later; if the DQM signal was
command will be truncated.
registered LOW, the DQs will provide valid data.
BURST TERMINATE
The BURST TERMINATE command is used to truncate either
READ or WRITE command prior to the BURST TERMINATE
13
Rev. 0.5, May. ‘07
FIDELIX [ FIDELIX ]
