IBMN312164CT3
IBMN312804CT3
IBMN312404CT3
Preliminary
128Mb Synchronous DRAM - Die Revision B
Data Mask
The SDRAM has a Data Mask function that can be used in conjunction with data read and write cycles. When
the Data Mask is activated (DQM high) during a write cycle, the write operation is prohibited immediately
(zero clock latency). If the Data Mask is activated during a read cycle, the data outputs are disabled and
become high impedance after a two-clock delay, independent of CAS latency.
Data Mask Activated during a Read Cycle
(Burst Length = 4, CAS Latency = 2)
T0
T1
T2
T3
T4
T5
T6
T7
T8
CK
DQM
NOP
READ A
NOP
NOP
NOP
NOP
NOP
NOP
NOP
COMMAND
DOUT A
DQs
DOUT A
1
0
A two-clock delay before
the DQs become Hi-Z
: “H” or “L”
No Operation Command
The No Operation Command should be used in cases when the SDRAM is in an idle or a wait state. The pur-
pose of the No Operation Command is to prevent the SDRAM from registering any unwanted commands
between operations. A No Operation Command is registered when CS is low with RAS, CAS, and WE held
high at the rising edge of the clock. A No Operation Command will not terminate a previous operation that is
still executing, such as a burst read or write cycle.
Deselect Command
The Deselect Command performs the same function as a No Operation Command. Deselect Command
occurs when CS is brought high, the RAS, CAS, and WE signals become don’t cares.
©IBM Corporation. All rights reserved.
06K7582.H03335A
01/01
Use is further subject to the provisions at the end of this document.
Page 27 of 66
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