W981216AH Datasheet, PDF (11/44 Pages) Winbond – 2M x 16 bit x 4 Banks SDRAM

W981216AH
2M x 16 bit x 4 Banks SDRAM
Burst Read Command
The Burst Read command is initiated by applying logic low level to CS and CAS while holding RAS and WE high at the rising
edge of the clock. The address inputs determine the starting column address for the burst. The Mode Register sets type of burst
(sequential or interleave) and the burst length (1, 2, 4, 8, full page) during the Mode Register Set Up cycle. Table 2 and 3 in the
next page explain the address sequence of interleave mode and sequence mode.
Burst Command
The Burst Write command is initiated by applying logic low level to CS, CAS and WE while holding RAS high at the rising
edge of the clock. The address inputs determine the starting column address. Data for the first burst write cycle must be applied
on the DQ pins on the same clock cycle that the Write Command is issued. The remaining data inputs must be supplied on each
subsequent rising clock edge until the burst length is completed. Data supplied to the DQ pins after burst finishes will be
ignored.
Read Interrupted by a Read
A Burst Read may be interrupted by another Read Command. When the previous burst is interrupted, the remaining addresses
are overridden by the new read address with the full burst length. The data from the first Read Command continues to appear on
the outputs until the CAS latency from the interrupting Read Command the is satisfied.
Read Interrupted by a Write
To interrupt a burst read with a Write Command, DQM may be needed to place the DQs (output drivers) in a high impedance
state to avoid data contention on the DQ bus. If a Read Command will issue data on the first and second clocks cycles of the
write operation, DQM is needed to insure the DQs are tri-stated. After that point the Write Command will have control of the
DQ bus and DQM masking is no longer needed.
Write Interrupted by a Write
A burst write may be interrupted before completion of the burst by another Write Command. When the previous burst is
interrupted, the remaining addresses are overridden by the new address and data will be written into the device until the
programmed burst length is satisfied.
Write Interrupted by a Read
A Read Command will interrupt a burst write operation on the same clock cycle that the Read Command is activated. The DQs
must be in the high impedance state at least one cycle before the new read data appears on the outputs to avoid data contention.
When the Read Command is activated, any residual data from the burst write cycle will be ignored.
Burst Stop Command
A Burst Stop Command may be used to terminate the existing burst operation but leave the bank open for future Read or Write
Commands to the same page of the active bank, if the burst length is full page. Use of the Burst Stop Command during other
burst length operations is illegal. The Burst Stop Command is defined by having RAS and CAS high with CS and WE low at the
rising edge of the clock. The data DQs go to a high impedance state after a delay which is equal to the CAS Latency in a burst
read cycle interrupted by Burst Stop. If a Burst Stop Command is issued during a full page burst write operation, then any
residual data from the burst write cycle will be ignored.
Revision 1.0
- 11 -
Publication Release Date: March, 1999