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4.1
Lecture5
MemoryChips
and
FiniteStateMachines
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4.2
MoreandMoreBits
Flip-flop:onesinglebit
Register:asetofbits
Registerfile:asetofregisters
Whatsnext?
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4.3
Memory
MemoryChip
Width=wordsize=mbits
Height=2^nwords
Bitsize=HeightxWidth
Addressn
]0..1[ mDin
]0..1[ mDout
Chip
select
Write
enable
Output
enable
m
m
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4.4
ErrorDetection
ParityGenerator
data
paritybit
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4.5
ErrorDetection
ParityGenerator
data
stored
parity
bit
comparator
computedparity
bit
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4.6
TypesofMemory
ROM:Read-OnlyMemoryPROM:ProgrammableROM
EPROM:Erasable(byUV)PROMEEPROM:ElectricallyErasablePROM
RAM:RandomAccessMemory
SRAM:StaticRAM
DRAM:DynamicRAM
Writetoitanytime,readfromitanytime.
Writetoitoff-line,readfromitanytime.
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4.7
SRAM
Storeeachbitinsidealatchanditsvalueremainsaslongasthechipispoweredup.
Accesstimeisfixed(maybedifferentforreadorwriteoperations).
Setupandholdtimesmustbeobservedfor
writes.
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4.8
DRAM
Thebitsarestoredincapacitorsratherthaninlatches.
Catch:capacitorsleakcharge=>mustrefreshperiodically.
Refreshingtakesonly1%to2%ofactivecycles.
CostislowerthanSRAM,butaccesstimeis
higher.
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4.9
SSRAMandSDRAM
Donthavetoaccessonewordatatime,butratherinchunksorbursts.
Giveitaaddressandburstlengthforeach
access.
Dontneedtopassoneaddressatatime,but
mustgiveitaclocksignaltosequentializeoperationswithinaburst.
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4.10
SequentialLogic
CombinationalLogic:Nomemory.
Whatextracapabilitieswoulda
circuitwithmemoryhave?
Memory
CombinationalLogicClock
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4.11
Whatsinastate?
Studytheproblemanddeterminewhat
informationneedstoberememberedbythe
circuitastimeevolves.
Thestateindicatesthecurrentcontentsof
memoryandwhatthevalueofanyoutput
linesthecircuitmayhave.
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4.12
Example:SequenceGenerator
(orCounter)
A/000
B/001
C/010
D/011
E/100
F/101
G/110H/111
Noneedforinputsotherthana
referencesignalfortimekeeping.
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4.13
Example:SequenceGenerator
(orCounter)
000111
111110110101
101100
100011
011010
010001
001000
Nextstate
(XYZ)
Currentstate(XYZ)
YZXZXYXX ++='
ZYZYY +='
ZZ ='
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4.14
SequenceGeneratorCircuitCombinationallogic=generatesnextstate(statetransitionfunction)
Memory=storescurrentstate
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4.15
Example:AnotherKindofCounter
A/000
B/001
C/010
D/011
E/100
F/101
G/110H/111
SinglebitinputWtellscircuittoeither
stoporgooncounting.
W=1
W=1
W=1
W=1
W=1
W=1
W=1W=1
W=0
W=0
W=0
W=0
W=0
W=0W=0
W=0
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4.16
Example:AnotherKindofCounter
1
0
1
0
1
0
1
0
W
011011
100011
010010
011010
001001
010001
000000
001000
Nextstate
(XYZ)
Current
state(XYZ)
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4.17
ASprinkleofFormalismMooreMachines
Memory
NextState
Function
Clock
Current
State Next
StateControl
Inputs
OutputGeneration
Circuit
Output
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4.18
ASprinkleofFormalismMealyMachines
Memory
NextState
Function
Clock
Current
State Next
StateControl
Inputs
OutputGeneration
Circuit
Output
