computing with switches and circuits (1)
TRANSCRIPT
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Computing with Switches and Circuits
Part 2
1004QBT
Foundations of ComputingSystems
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Lecture !"ecti#e
• This wee$% we&'' continue to 'oo$ ate'ectrica' circuits that wou'd !e usedinside your computer
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QUIZ TIME!
(wahahaha
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LAST WEEK
)e#ision
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Last *ee$
• Boo'ean 'ogic gates – +,-
– )
–,T
– ,)
– ,+,-
– .)
• /'ectromechanica'and 'ogica' circuits
• Binarymathematics – -ecima' to !inary
– Binary to decima'
–
Binary addition%su!traction%mu'tip'ication%di#ision
•
(athematica'circuits – a'fadder
– Fu''adder
– (u'tip'eor
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ow does a #on ,eumann machineuse Boo'ean and +rithmetic circuits3
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STORAGE CIRCUITS
Computer memory
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Storage in a vonNeumann Macine
The CP registers are made upof a series of fip-fops5
*e&'' 'oo$ at how to !ui'd 6ip6ops and how they wor$5
Before we get there% we needto 'oo$ at some of thecomponents5
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Feed!ac$
• To store information% circuits musteedback into each other5
• + set/reset (SR) latch does this usingtwo ,) gates
,or gates7 re'ay diagram of de (organ #ariant% and !oth #ersions of 'ogica'
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S) Latches in peration
+n S) 'atch with the reset 'inemo#ing from o8 to on
+n S) 'atch with the reset 'inemo#ing from on to o8
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S) Latches in peration
+n S) 'atch with the reset 'inemo#ing from o8 to on
+n S) 'atch with the reset 'inemo#ing from on to o8
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S) Latches in peration
+n S) 'atch with the set 'inemo#ing from o8 to on
+n S) 'atch with the set 'inemo#ing from on to o8
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S) Latches in peration
+n S) 'atch with the set 'inemo#ing from o8 to on
+n S) 'atch with the set 'inemo#ing from on to o8
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Latches and Fetch/ecute
• *e can now ma$e our computer remem!erone !it per S) Latch5
• 9n a #on ,eumann machine% we want to !e
a!'e to update a'' 'atches at the same time5• 9n the Fetch/ecute cyc'e% we used the
c'oc$ to synchronise actions5 *e can do thesame thing here5
• *e ca'' the new 'atch a datatype :-type;'atch
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-type Latch,T
switch
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-type 'atch in Logisim
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Te S"tem C#oc$
The c'oc$ sends an osci''ating signa'5 The -type 'atchcan on'y update when the c'oc$ signa' is high5therwise% the +,- circuit wi'' not !e c'osed andcurrent can&t 6ow to the S/T or )/S/T inputs of the S)
'atch5
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-type Latch
• There is one specia'case where this -type'atch won&t wor$ as weepect5
• )emem!er that in a#on ,eumannmachine% ca'cu'ationshad operands that
speci
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Te &'t(e )#i( )#o(
+ 6ip6op uses two 'atches% one to ho'd the current state%and the other to o#erwrite when the ,T instruction iscomp'eted5
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Te &'t(e )#i( )#o(+ 6ip6op uses two 'atches% one to ho'd the current state%and the other to o#erwrite when the ,T instruction iscomp'eted5
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CP )egisters
• *e ha#e now seen how to !ui'd CPregisters5
• To store > !its% you wou'd use > -type 6ip6ops in para''e'5
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*OOLEAN SELECTION
ow to ma$e the 9nstructions wor$
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Performing Computations
• 9n a #on ,eumann machine% the instructionregister is connected to the other registersand the +L in such a way that entering
the instruction causes a cascade thatupdates a'' re'e#ant registers e#ery c'oc$tic$5
• -uring the etch of the fetcheecute cyc'e%
an instruction is 'oaded into the instructionregister5
• 9t then gets decoded5
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The -ecoder
• 9nstructions areentered as a !inarynum!er5
•
perations are !ui'tinto your computer ascircuits5
• The decoder is a
circuit which ta$esthe input num!er anduses it to acti#ate aparticu'ar output 'ine5
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(u'tip'eing
• nce the decoderhas se'ected anoutput% we can use
a mu'tip'eor tose'ect one set ofdata5
• This data can come
from a register% or!e the output of anoperation5
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-emu'tip'eing
• *e can a'so go theopposite way%using a
demultiplexor todecide where tosend one !it ofdata5
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*UIL&ING T+E C,U
Putting the pieces together
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+L
• *e can put a'' ourarithmetic and 'ogiccircuits together tocreate an +L5
• *e can ha#e mu'tip'e+Ls in para''e' to domu'tip'e !its ofca'cu'ation5
• ,ote that a mu'tip'eoris used to se'ect oneoutput from the +L5
( u
' t i p ' e 2
o r
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9nstruction )egister
• The opcode of the instructionregister is used to se'ect an outputfrom an operations a#ai'a!'e on the
+L5
• The operands of the +L are used tose'ect an input from the CP
registers% to !e fed into the +L5
• ?ou now ha#e e#erything you need to
!ui'd a CP or a ca'cu'atorA