W9864G2GH Datasheet, PDF (8/46 Pages) Winbond – 512K X 4 BANKS X 32BITS SDRAM

W9864G2GH
7. FUNCTIONAL DESCRIPTION
7.1 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_CCQ 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 VCC + 0.3V on
any of the input pins or VCC 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.
7.2 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 tRSC has
elapsed. Please refer to the next page for Mode Register Set Cycle and Operation Table.
7.3 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 (tRCD). 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 (tRC).
The minimum time interval between interleaved Bank Activate commands (Bank A to Bank B and vice
versa) is the Bank to Bank delay time (tRRD). The maximum time that each bank can be held active is
specified as TRAS (max.).
7.4 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 tRCD 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.
Publication Release Date:Aug. 13, 2007
-8-
Revision A09