IS42S16400F
IC42S16400F
CAS Latency
Operating Mode
TheꢀCASꢀlatencyꢀisꢀtheꢀdelay,ꢀinꢀclockꢀcycles,ꢀbetweenꢀ
the registrationꢀofꢀaꢀREADꢀcommandꢀandꢀtheꢀavailabilityꢀofꢀ
theꢀfirstꢀpieceꢀofꢀoutputꢀdata.ꢀTheꢀlatencyꢀcanꢀbeꢀsetꢀtoꢀtwoꢀorꢀ
three clocks.
TheꢀnormalꢀoperatingꢀmodeꢀisꢀselectedꢀbyꢀsettingꢀM7ꢀandꢀM8ꢀ
toꢀzero;ꢀtheꢀotherꢀcombinationsꢀofꢀvaluesꢀforꢀM7ꢀandꢀM8ꢀareꢀ
reservedꢀforꢀfutureꢀuseꢀand/orꢀtestꢀmodes.ꢀTheꢀprogrammedꢀ
burstꢀlengthꢀappliesꢀtoꢀbothꢀREADꢀandꢀWRITEꢀbursts.
IfꢀaꢀREADꢀcommandꢀisꢀregisteredꢀatꢀclockꢀedgeꢀn,ꢀandꢀ
the latency is m clocks, the data will be available by clock
edge n + m.ꢀTheꢀDQsꢀwillꢀstartꢀdrivingꢀasꢀaꢀresultꢀofꢀtheꢀ
clock edge one cycle earlier (n + m - 1), and provided that
the relevant access times are met, the data will be valid by
clock edge n + m.ꢀForꢀexample,ꢀassumingꢀthatꢀtheꢀclockꢀ
cycle time is such that all relevant access times are met,
ifꢀaꢀREADꢀcommandꢀisꢀregisteredꢀatꢀT0ꢀandꢀtheꢀlatencyꢀ
isꢀprogrammedꢀtoꢀtwoꢀclocks,ꢀtheꢀDQsꢀwillꢀstartꢀdrivingꢀ
afterꢀT1ꢀandꢀtheꢀdataꢀwillꢀbeꢀvalidꢀbyꢀT2,ꢀasꢀshownꢀinꢀCASꢀ
Latencyꢀdiagrams.ꢀTheꢀAllowable Operating Frequency
table indicates the operating frequencies at which each
CAS latency setting can be used.
Testꢀmodesꢀandꢀreservedꢀstatesꢀshouldꢀnotꢀbeꢀusedꢀbe-
cause unknown operation or incompatibility with future
versions may result.
Write Burst Mode
When M9 = 0, the burst length programmed via M0-M2
appliesꢀtoꢀbothꢀREADꢀandꢀWRITEꢀbursts;ꢀwhenꢀM9ꢀ=ꢀ1,ꢀ
theꢀprogrammedꢀburstꢀlengthꢀappliesꢀtoꢀREADꢀbursts,ꢀbutꢀ
write accesses are single-location (nonburst) accesses.
CAS Latency
Allowable Operating Frequency (MHz)
Speed
CAS Latency = 2
CAS Latency = 3
Reservedꢀstatesꢀshouldꢀnotꢀbeꢀusedꢀasꢀunknownꢀoperationꢀ
or incompatibility with future versions may result.
5
6
7
133
133
133
200
166
143
CAS Latency
T0
T1
T2
T3
CLK
READ
NOP
NOP
COMMAND
DQ
t
AC
D
OUT
OH
t
LZ
t
CAS Latency - 2
T0
T1
T2
T3
T4
CLK
READ
NOP
NOP
NOP
COMMAND
DQ
t
AC
D
OUT
OH
t
LZ
t
CAS Latency - 3
DON'T CARE
UNDEFINED
18
Integrated Silicon Solution, Inc. — www.issi.com
Rev. A
03/19/08
ISSI [ INTEGRATED SILICON SOLUTION, INC ]
