Computing With Switches and Circuits (1)

8/18/2019 Computing With Switches and Circuits (1)

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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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+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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+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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+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

Documents

Computing With Switches and Circuits (1)