64Mb: x32
SDRAM
READs
READ bursts are initiated with a READ command,
as shown in Figure 5.
The starting column and bank addresses are pro-
vided with the READ command, and auto precharge is
either enabled or disabled for that burst access. If auto
precharge is enabled, the row being accessed is
precharged at the completion of the burst. For the ge-
neric READ commands used in the following illustra-
tions, auto precharge is disabled.
During READ bursts, the valid data-out element
from the starting column address will be available fol-
lowing the CAS latency after the READ command. Each
subsequent data-out element will be valid by the next
positive clock edge. Figure 6 shows general timing for
each possible CAS latency setting.
Upon completion of a burst, assuming no other com-
mands have been initiated, the DQs will go High-Z. A
full-page burst will continue until terminated. (At the
end of the page, it will wrap to column 0 and continue.)
Data from any READ burst may be truncated with a
subsequent READ command, and data from a fixed-
length READ burst may be immediately followed by
data from a READ command. In either case, a continu-
ous flow of data can be maintained. The first data ele-
ment from the new burst follows either the last ele-
ment of a completed burst or the last desired data ele-
ment of a longer burst that is being truncated. The new
READ command should be issued
x
cycles before the
clock edge at which the last desired data element is
valid, where
x
equals the CAS latency minus one. This
is shown in Figure 7 for CAS latencies of one, two and
Figure 5
READ Command
CLK
CKE
CS#
HIGH
T0
CLK
COMMAND
Figure 6
CAS Latency
T1
T2
READ
tLZ
NOP
tOH
D
OUT
DQ
tAC
CAS Latency = 1
RAS#
T0
T1
T2
T3
CAS#
CLK
COMMAND
WE#
READ
NOP
tLZ
NOP
tOH
D
OUT
DQ
A0–A7
A8, A9
COLUMN
ADDRESS
tAC
CAS Latency = 2
ENABLE AUTO PRECHARGE
T0
CLK
T1
T2
T3
T4
A10
DISABLE AUTO PRECHARGE
COMMAND
READ
NOP
NOP
tLZ
NOP
tOH
D
OUT
BA0, 1
BANK
ADDRESS
DQ
tAC
CAS Latency = 3
DON’T CARE
UNDEFINED
64Mb: x32 SDRAM
64MSDRAMx32_5.p65 – Rev. B; Pub. 6/02
13
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©2002, Micron Technology, Inc.
MICRON [ MICRON TECHNOLOGY ]
