W981616AH
Auto-precharge Command
If A10 is set to high when the Read or Write Command is issued, then the auto-precharge function is
entered. During auto-precharge, a Read Command will execute as normal with the exception that the
active bank will begin to precharge automatically before all burst read cycles have been completed.
Regardless of burst length, it will begin a certain number of clocks prior to the end of the scheduled
burst cycle. The number of clocks is determined by
CAS
latency.
A Read or Write Command with auto-precharge can not be interrupted before the entire burst
operation is completed. Therefore, use of a Read, Write, or Precharge Command is prohibited during
a read or write cycle with auto-precharge. Once the precharge operation has started, the bank cannot
be reactivated until the Precharge time (t
RP
) has been satisfied. Issue of Auto-Precharge command is
illegal if the burst is set to full page length. If A10 is high when a Write Command is issued, the Write
with Auto-Precharge function is initiated. The SDRAM automatically enters the precharge operation
one clock delay from the last burst write cycle. This delay is referred to as Write t
DPL
. The bank
undergoing auto-precharge can not be reactivated until t
DPL
and t
RP
are satisfied. This is referred to as
t
DAL
, Data-in to Active delay (t
DAL
= t
DPL
+ t
RP
). When using the Auto-precharge Command, the interval
between the Bank Activate Command and the beginning of the internal precharge operation must
satisfy t
RAS
(min).
Precharge Command
The Precharge Command is used to precharge or close a bank that has been activated. The
Precharge Command is entered when
CS
,
RAS
and
WE
are low and
CAS
is high at the rising edge
of the clock. The Precharge Command can be used to precharge each bank separately or all banks
simultaneously. Three address bits, A10, and BA, are used to define which bank(s) is to be
precharged when the command is issued. After the Precharge Command is issued, the precharged
bank must be reactivated before a new read or write access can be executed. The delay between the
Precharge Command and the Activate Command must be greater than or equal to the Precharge
time (t
RP
).
Self Refresh Command
The Self-Refresh Command is defined by having
CS
,
RAS
,
CAS
and CKE held low with
WE
high
at the rising edge of the clock. All banks must be idle prior to issuing the Self-Refresh Command.
Once the command is registered, CKE must be held low to keep the device in Self-Refresh mode.
When the SDRAM has entered Self Refresh mode all of the external control signals, except CKE, are
disabled. The clock is internally disabled during Self-Refresh Operation to save power. The device
will exit Self-Refresh operation after CKE is returned high. Any subsequent commands can be issued
after t
RC
from the end of Self Refresh command.
If, during normal operation, Auto-Refresh cycles are issued in bursts (as opposed to being evenly
distributed), a burst of 4,096 Auto-Refresh cycles should be completed just prior to entering and just
after exiting the Self-Refresh mode.
Power Down Mode
The Power Down mode is initiated by holding CKE low. All of the receiver circuits except CKE are
gated off to reduce the power. The Power Down mode does not perform any refresh operations;
therefore the device can not remain in Power Down mode longer than the Refresh period (t
REF
) of the
device.
Publication Release Date: February 2000
Revision A2
-7-
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