1M x 16 SDRAM
CAS# latency=1, 2, 3
Input data for the Write is masked.
Termination of a Burst Write Operation (Burst Length = X, CAS# Latency = 1, 2, 3)
10 Device Deselect command
(CS# = "H")
The Device Deselect command disables the command decoder so that the RAS#, CAS#, WE#
and Address inputs are ignored, regardless of whether the CLK is enabled. This command is similar
to the No Operation command.
11 AutoRefresh command (refer to Figures 3 & 4 in Timing Waveforms)
(RAS# = "L", CAS# = "L", WE# = "H",CKE = "H", A11 = “Don‘t care, A0-A9 = Don't care)
The AutoRefresh command is used during normal operation of the SDRAM and is analogous to
CAS#-before-RAS# (CBR) Refresh in conventional DRAMs. This command is non-persistent, so it
must be issued each time a refresh is required. The addressing is generated by the internal refresh
controller. This makes the address bits a "don't care" during an AutoRefresh command. The internal
refresh counter increments automatically on every auto refresh cycle to all of the rows. The refresh
operation must be performed 2048 times within 32ms. The time required to complete the auto
refresh operation is specified by tRC(min.). To provide the AutoRefresh command, both banks need
to be in the idle state and the device must not be in power down mode (CKE is high in the previous
cycle). This command must be followed by NOPs until the auto refresh operation is completed. The
precharge time requirement, tRP(min), must be met before successive auto refresh operations are
12 SelfRefresh Entry command (refer to Figure 5 in Timing Waveforms)
(RAS# = "L", CAS# = "L", WE# = "H", CKE = "L", A0-A9 = Don't care)
The SelfRefresh is another refresh mode available in the SDRAM. It is the preferred refresh
mode for data retention and low power operation. Once the SelfRefresh command is registered, all
the inputs to the SDRAM become "don't care" with the exception of CKE, which must remain LOW.
The refresh addressing and timing is internally generated to reduce power consumption. The
SDRAM may remain in SelfRefresh mode for an indefinite period. The SelfRefresh mode is exited
by restarting the external clock and then asserting HIGH on CKE (SelfRefresh Exit command).
13 SelfRefresh Exit command (refer to Figure 5 in Timing Waveforms)
(CKE = "H", CS# = "H" or CKE = "H", RAS# = "H", CAS# = "H", WE# = "H")
This command is used to exit from the SelfRefresh mode. Once this command is registered,
NOP or Device Deselect commands must be issued for tRC(min.) because time is required for the
completion of any bank currently being internally refreshed. If auto refresh cycles in bursts are
performed during normal operation, a burst of 4096 auto refresh cycles should be completed just
prior to entering and just after exiting the SelfRefresh mode.
Rev. 1.1 Apr. 2005