Integrated Silicon Solution, Inc. — www.issi.com —
1-800-379-4774
19
Rev. 00D
06/02/08
IS42S32200E
DON'T CARE
UNDEFINED
CLK
COMMAND
DQ
READ NOP NOP NOP
CAS Latency - 3
tAC
tOH
DOUT
T0 T1 T2 T3 T4
tLZ
CLK
COMMAND
DQ
READ NOP NOP
CAS Latency - 2
tAC
tOH
DOUT
T0 T1 T2 T3
tLZ
CAS Latency
same bank. The PRECHARGE 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 the READ to PRECHARGE
diagram for each possible CAS latency; data element
n
+
3 is either the last of a burst of four or the last desired of a
longer burst. Following the PRECHARGE command, a
subsequent command to the same bank cannot be issued
until tRP is met. Note that part of the row precharge time is
hidden during the access of the last data element(s).
In the case of a fixed-length burst being executed to
completion, a PRECHARGE command issued at the
optimum time (as described above) provides the same
operation that would result from the same fixed-length
burst with auto precharge. The disadvantage of the
PRECHARGE command is that it requires that the com-
mand and address buses be available at the appropriate
time to issue the command; the advantage of the
PRECHARGE command is that it can be used to truncate
fixed-length or full-page bursts.
Full-page READ bursts can be truncated with the BURST
TERMINATE command, and fixed-length READ bursts
may be truncated with a BURST TERMINATE command,
provided that auto precharge was not activated. The
BURST TERMINATE 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 the READ Burst Termination
diagram for each possible CAS latency; data element
n
+
3 is the last desired data element of a longer burst.
