W981216AH Datasheet, PDF (10/44 Pages) Winbond – 2M x 16 bit x 4 Banks SDRAM

W981216AH
Functional Description
2M x 16 bit x 4 Banks SDRAM
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 VCC and VCCQ 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 200us 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 tRSC 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 (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).
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.
Revision 1.0
- 10 -
Publication Release Date: March, 1999