EtronTech
Commands
1
EM63A165
BankActivate
(RAS# = "L", CAS# = "H", WE# = "H", BAs = Bank, A0-A12 = Row Address)
The BankActivate command activates the idle bank designated by the BA0,1 signals. By
latching the row address on A0 to A12 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 t
RCD
(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 t
RC
(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 four banks.
t
RRD
(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
..............
ADDRESS
Bank A
Row Addr.
RAS# - CAS# delay (
t
RCD
)
Bank A
Col Addr.
..............
Bank B
Row Addr.
RAS# - RAS# delay time (
t
RRD
)
Bank A
Row Addr.
COMM AND
Bank A
Activate
NOP
NOP
R/W A with
AutoPrecharge
..............
Bank B
Activate
NOP
NOP
Bank A
Activate
RAS# Cycle time (
t
RC
)
AutoPrecharge
Begin
: "H" or "L"
BankActivate Command Cycle
(Burst Length = n, CAS# Latency = 3)
2
BankPrecharge command
(RAS# = "L", CAS# = "H", WE# = "L", BAs = Bank, A10 = "L", A0-A9, A11 and A12 = Don't care)
The BankPrecharge command precharges the bank disignated by BA signal. The precharged
bank is switched from the active state to the idle state. This command can be asserted anytime after
t
RAS
(min.) is satisfied from the BankActivate command in the desired bank. The maximum time any
bank can be active is specified by t
RAS
(max.). Therefore, the precharge function must be performed in
any active bank within t
RAS
(max.). At the end of precharge, the precharged bank is still in the idle state
and is ready to be activated again.
PrechargeAll command
(RAS# = "L", CAS# = "H", WE# = "L", BAs = Don’t care, A10 = "H", A0-A9, A11 and A12 = 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 t
RCD
(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).
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4
6
Rev 1.1 Apr. 2007