W981616AH
FUNCTIONAL DESCRIPTION
Power Up and Initialization
The default power up state of the mode register is unspecified. The following power up and
initialization sequence need to be followed to guarantee the device being preconditioned to each user
specific needs during power up, all V
CC
and V
CC
Q pins must be ramp up simultaneously to the
specified voltage when the input signals are held in the "NOP" state. The power up voltage must not
exceed V
CC
+0.3V on any of the input pins or V
CC
supplies. After power up, an initial pause of 200
µS
is required followed by a precharge of all banks using the precharge command. To prevent data
contention on the DQ bus during power up, it is required that the DQM and CKE pins be held high
during the initial pause period. Once all banks have been precharged, the Mode Register Set
Command must be issued to initialize the Mode Register. An additional eight Auto Refresh cycles
(CBR) are also required before or after programming the Mode Register to ensure proper subsequent
operation.
Programming Mode Register
After initial power up, the Mode Register Set Command must be issued for proper device operation.
All banks must be in a precharged state and CKE must be high at least one cycle before the Mode
Register Set Command can be issued. The Mode Register Set Command is activated by the low
signals of
RAS
,
CAS
,
CS
and
WE
at the positive edge of the clock. The address input data during
this cycle defines the parameters to be set as shown in the Mode Register Operation table. A new
command may be issued following the mode register set command once a delay equal to t
RSC
has
elapsed. Please refer to the next page for Mode Register Set Cycle and Operation Table.
Bank Activate Command
The Bank Activate command must be applied before any Read or Write operation can be executed.
The operation is similar to
RAS
activate in EDO DRAM. The delay from when the Bank Activate
command is applied to when the first read or write operation can begin must not be less than the RAS
to CAS delay time (t
RCD
). Once a bank has been activated it must be precharged before another Bank
Activate command can be issued to the same bank. The minimum time interval between successive
Bank Activate commands to the same bank is determined by the RAS cycle time of the device (t
RC
).
The minimum time interval between interleaved Bank Activate commands (Bank A to Bank B and
vice versa) is the Bank-to-Bank delay time (t
RRD
). The maximum time that each bank can be held
active is specified as t
RAS
(max.).
Read and Write Access Modes
After a bank has been activated, a read or write cycle can be followed. This is accomplished by
setting RAS high and CAS low at the clock rising edge after minimum of t
RCD
delay. WE pin voltage
level defines whether the access cycle is a read operation ( WE high), or a write operation ( WE low).
The address inputs determine the starting column address. Reading or writing to a different row within
an activated bank requires the bank be precharged and a new Bank Activate command be issued.
When more than one bank is activated, interleaved bank Read or Write operations are possible. By
using the programmed burst length and alternating the access and precharge operations between
multiple banks, seamless data access operation among many different pages can be realized. Read
or Write Commands can also be issued to the same bank or between active banks on every clock
cycle.
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