AS4C8M16SA
Commands
1
BankActivate
(RAS# = "L", CAS# = "H", WE# = "H", BAs = Bank, A0-A11 = Row Address)
The BankActivate command activates the idle bank designated by the BA0, 1 signals. By latching
the row address on A0 to A11 at the time of this command, the selected row access is initiated. The read
or write operation in the same bank can occur after a time delay of tRCD (min.) from the time of bank
activation. A subsequent BankActivate command to a different row in the same bank can only be issued
after the previous active row has been precharged (refer to the following figure). The minimum time
interval between successive BankActivate commands to the same bank is defined by tRC (min.). The
SDRAM has four internal banks on the same chip and shares part of the internal circuitry to reduce chip
area; therefore it restricts the back-to-back activation of the two banks. tRRD (min.) specifies the minimum
time required between activating different banks. After this command is used, the Write command and the
Block Write command perform the no mask write operation.
T0
T1
T2
T3
Tn+3 Tn+4
Tn+5
Tn+6
CLK
Bank A
Bank A
Bank B
Bank A
ADDRESS
COMMAND
Row Addr.
Col Addr.
Row Addr.
Row Addr.
RAS# - CAS# delay(tRCD
)
RAS# - RAS# delay time(tRRD)
Bank A
Activate
Bank B
Activate
Bank A
Activate
R/W A with
AutoPrecharge
NOP
NOP
NOP
NOP
RAS# - Cycle time(tRC
)
AutoPrecharge
Begin
Don’t Care
Figure 3. BankActivate Command Cycle
(Burst Length = n)
2
BankPrecharge command
(RAS# = "L", CAS# = "H", WE# = "L", BAs = Bank, A10 = "L", A0-A9 and A11 = Don't care)
The BankPrecharge command precharges the bank designated by BA signal. The precharged bank
is switched from the active state to the idle state. This command can be asserted anytime after tRAS(min.)
is satisfied from the BankActivate command in the desired bank. The maximum time any bank can be
active is specified by tRAS(max.). Therefore, the precharge function must be performed in any active bank
within tRAS(max.). At the end of precharge, the precharged bank is still in the idle state and is ready to be
activated again.
3
4
PrechargeAll command
(RAS# = "L", CAS# = "H", WE# = "L", BAs = Don’t care, A10 = "H", A0-A9 and A11 = Don't care)
The PrechargeAll command precharges all banks simultaneously and can be issued even if all banks
are not in the active state. All banks are then switched to the idle state.
Read command
(RAS# = "H", CAS# = "L", WE# = "H", BAs = Bank, A10 = "L", A0-A8 = Column Address)
The Read command is used to read a burst of data on consecutive clock cycles from an active row in
an active bank. The bank must be active for at least tRCD (min.) before the Read command is issued.
During read bursts, the valid data-out element from the starting column address will be available following
the CAS latency after the issue of the Read command. Each subsequent data-out element will be valid by
the next positive clock edge (refer to the following figure). The DQs go into high-impedance at the end of
the burst unless other command is initiated. The burst length, burst sequence, and CAS latency are
determined by the mode register, which is already programmed. A full-page burst will continue until
terminated (at the end of the page it will wrap to column 0 and continue).
Confidential
7
Rev. 2.2
Mar /2014
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
