IS42S81600D, IS42S16800D
ACTIVATING SPECIFIC ROW WITHIN SPE-
CIFIC BANK
CHIP OPERATION
BANK/ROW ACTIVATION
BeforeanyREADorWRITEcommandscanbeissuedtoa
bankwithintheSDRAM,arowinthatbankmustbe“opened.”
This is accomplished via the ACTIVE command, which
selects both the bank and the row to be activated (see
Activating Specific Row Within Specific Bank).
CLK
HIGH
CKE
CS
After opening a row (issuing an ACTIVE command), a
READ or WRITE command may be issued to that row,
subject to the tRCD specification. Minimum tRCD should be
dividedbytheclockperiodandroundeduptothenextwhole
number to determine the earliest clock edge after the
ACTIVE command on which a READ or WRITE command
can be entered. For example, a tRCD specification of 18ns
with a 125 MHz clock (8ns period) results in 2.25 clocks,
rounded to 3. This is reflected in the following example,
which covers any case where 2 < [tRCD (MIN)/tCK] ≤ 3. (The
sameprocedureisusedtoconvertotherspecificationlimits
from time units to clock cycles).
RAS
CAS
WE
A0-A11
BA0, BA1
ROW ADDRESS
BANK ADDRESS
A subsequent ACTIVE command to a different row in the
samebankcanonlybeissuedafterthepreviousactiverow
hasbeen“closed”(precharged).Theminimumtimeinterval
betweensuccessiveACTIVEcommandstothesamebank
is defined by tRC.
A subsequent ACTIVE command to another bank can be
issuedwhilethefirstbankisbeingaccessed, whichresults
in a reduction of total row-access overhead. The minimum
time interval between successive ACTIVE commands to
different banks is defined by tRRD.
EXAMPLE: MEETING TRCD (MIN) WHEN 2 < [TRCD (MIN)/TCK] ≤ 3
T0
T1
T2
T3
T4
CLK
READ or
WRITE
ACTIVE
NOP
NOP
COMMAND
tRCD
DON'T CARE
Integrated Silicon Solution, Inc. — www.issi.com
27
Rev. E
07/28/08
ISSI [ INTEGRATED SILICON SOLUTION, INC ]
