Datasheet

9 No-Operation command
(RAS# = "H", CAS# = "H", WE# = "H")
The No-Operation command is used to perform a NOP to the SDRAM which is selected (CS# is Low).
This prevents unwanted commands from being registered during idle or wait states.
10 Burst Stop command
(RAS# = "H", CAS# = "H", WE# = "L")
The Burst Stop command is used to terminate either fixed-length or full-page bursts. This command is
only effective in a read/write burst without the auto precharge function. The terminated read burst ends
after a delay equal to the CAS latency (refer to the following figure). The termination of a write burst is
shown in the following figure.
CLK
COMMAND
T0 T1 T2 T3 T4 T5 T6
READ A NOP NOP NOP
Burst
Stop
NOP NOP NOP
T7 T8
NOP
CAS# Latency=2
t
CK2
, DQ
CAS# Latency=3
t
CK3
, DQ
DOUT A
0
DOUT A
1
DOUT A
2
DOUT A
3
DOUT A
0
DOUT A
1
DOUT A
2
DOUT A
3
The burst ends after a delay equal to the CAS# Latency
Figure 16. Termination of a Burst Read Operation
(Burst Length
＞
4, CAS# Latency = 2, 3)
CLK
DQ
T0 T1 T2 T3 T4 T5 T6
DIN A
0
DIN A
1
DIN A
2
don’t care
T7 T8
COMMAND
NOP WRITE A NOP NOP
Burst
Stop
NOP NOP NOP NOP
Figure 17. Termination of a Burst Write Operation
(Burst Length = X)
11 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.
12 AutoRefresh command
(RAS# = "L", CAS# = "L", WE# = "H", CKE = "H", A0-A11 = 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 4096 times within 64ms. The time required to complete the auto refresh operation is specified
by t
RC
(min.). To provide the AutoRefresh command, all 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, t
RP
(min), must be
met before successive auto refresh operations are performed.
AS4C4M16SA-C&I
Confidential
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Rev.5.0 October 2018