M13S32321A_08 Datasheet, PDF (21/50 Pages) Elite Semiconductor Memory Technology Inc. – 256K x 32 Bit x 4 Banks Double Data Rate SDRAM

ESMT
M13S32321A
Write Interrupted by a Read & DM
A burst write can be interrupted by a read command of any bank. The DQ’s must be in the high impedance state at least one
clock cycle before the interrupting read data appear on the outputs to avoid data contention. When the read command is registered,
any residual data from the burst write cycle must be masked by DM. The delay from the last data to read command (t_WTR) is
required to avoid the data contention DRAM inside. Data that are presented on the DQ pins before the read command is initiated
will actually be written to the memory. Read command interrupting write can not be issued at the next clock edge of that of write
command.
<Burst Length = 8, CAS Latency = 3>
0
1
CLK
CLK
2
3
4
5
6
COMMAND
NOP
CAS Latency=3
DQS
DQ's
CAS Latency=3
DQS
DQ's
W RITE
NOP
tDQSSmax
NOP
NOP
Read
tWTR
NOP
tWPRES
tDQSSmin
Din 0 Din 1 Din 2 Din 3 Din 4 Din 5 Din 6 Din 7
tWTR
tWPRES
Din 0 Din 1 Din 2 Din 3 Din 4 Din 5 Din 6 Din 7
7
8
NOP
NOP
Dout 0 Dout 1
Dout 0 Dout 1
DM
The following functionality established how a Read command may interrupt a Write burst and which input data is not written into
the memory.
1. For Read commands interrupting a Write burst, the minimum Write to Read command delay is 2 clock cycles. The case where
the Write to Read delay is 1 clock cycle is disallowed.
2. For read commands interrupting a Write burst, the DM pin must be used to mask the input data words which immediately
precede the interrupting Read operation and the input data word which immediately follows the interrupting Read operation.
3. For all cases of a Read interrupting a Write, the DQ and DQS buses must be released by the driving chip (i.e., the memory
controller) in time to allow the buses to turn around before the SDRAM drives them during a read operation.
4. If input Write data is masked by the Read command, the DQS inputs is ignored by the SDRAM.
5. It is illegal for a Read command interrupt a Write with autoprecharge command.
Elite Semiconductor Memory Technology Inc.
Publication Date : Jul. 2008
Revision : 1.1
21/50