ESMT
M13S5121632A (2R)
Write Interrupted by a Precharge & DM
A burst write operation can be interrupted before completion of the burst by a precharge of the same bank. Random column
access is allowed. A write recovery time (tWR) is required from the last data to precharge command. When precharge command
is asserted, any residual data from the burst write cycle must be masked by DM.
<Burst Length = 8>
0
1
2
3
4
5
6
7
8
C L K
C L K
N O P
WRITE A
t
N O P
N O P
WRITE B
N O P
N O P
N O P
Precharge A
C O M M A N D
t
W R
D Q S S ( m a x
)
H i - Z
H i - Z
D Q S
* 5
W P R E S
t
D
INA0
D
INA5
DINB0
D
INA1
D
INA2
D
INA3
D
INA6
D
INA7
D Q ' s
D M
D
INA4
t
W R
t
D Q S S ( m i n )
H i - Z
H i - Z
D Q S
D Q ' s
D M
t
W P R E S * 5
D
INA0
D
INA5
DINB1
D
INA1
D
INA2
D
INA3
D
INA6
D
INA7
DINB0
D
INA4
Precharge timing for Write operations in DRAMs requires enough time to allow “write recovery” which is the time required by a
DRAM core to properly store a full “0” or “1” level before a Precharge operation. For DDR SDRAM, a timing parameter, tWR, is used
to indicate the required of time between the last valid write operation and a Precharge command to the same bank.
tWR starts on the rising clock edge after the last possible DQS edge that strobed in the last valid and ends on the rising clock edge
that strobes in the precharge command.
1. For the earliest possible Precharge command following a Write burst without interrupting the burst, the minimum time for write
recovery is defined by tWR
.
2. When a precharge command interrupts a Write burst operation, the data mask pin, DM, is used to mask input data during the
time between the last valid write data and the rising clock edge in which the Precharge command is given. During this time, the
DQS input is still required to strobe in the state of DM. The minimum time for write recovery is defined by tWR
.
3. For a Write with auto precharge command, a new Bank Activate command may be issued to the same bank after tWR + tRP where
tWR + tRP starts on the falling DQS edge that strobed in the last valid data and ends on the rising clock edge that strobes in the
Bank Activate commands. During write with auto precharge, the initiation of the internal precharge occurs at the same time as the
earliest possible external Precharge command without interrupting the Write burst as described in 1 above.
4. In all cases, a Precharge operation cannot be initiated unless tRAS(min) [minimum Bank Activate to Precharge time] has been
satisfied. This includes Write with auto precharge commands where tRAS(min) must still be satisfied such that a Write with auto
precharge command has the same timing as a Write command followed by the earliest possible Precharge command which does
not interrupt the burst.
5. Refer to “Burst write operation”
Elite Semiconductor Memory Technology Inc.
Publication Date : Feb. 2013
Revision : 1.3 23/48
ESMT [ ELITE SEMICONDUCTOR MEMORY TECHNOLOGY INC. ]
