1/2550a. yaicharoen1 logic design with msi circuits...

1/2550 A. Yaicharoen 1

Logic Design with MSI Circuits

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Type of Circuits

Type of circuits Number of gates Small-scale integration (SSI) 1-10

Medium-scale integration (MSI) 10-100

Large-scale integration (LSI) 100-1,000

Very-large-scale integration (VLSI) 1,000 up

หมีายเหต� หน�งส(อบางเล มีแบ งวังจัรท��มี�เกต ต�)งแต 1,000,000 เกต ข*)นไป ให�อย� ใน กล� มี ULSI (Ultra-large-scale

integration)


Multiplexers (MUXs)

- also called a data selectorInput lines consist of- data lines: 2n lines- select lines: n lines- there may or may not be an

enable line Output line:- output line: 1 line


Multiplexer Function

-Truth table of a 4:1 multiplexer (without enable)

Select inputs Output

S1 S0 Y

0 0 I0

0 1 I1

1 0 I2

1 1 I3

€

Y = S1.S0.I0 + S1.S0.I1 + S1.S0.I2 + S1.S0.I3


Multiplexer Function

-Truth table of a 4:1 multiplexer (with enable)Enable Select inputs Output

E S1 S0 Y

0 X X 0

1 0 0 I0

1 0 1 I1

1 1 0 I2

1 1 1 I3

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Y = E .(S1.S0.I0 + S1.S0.I1 + S1.S0.I2 + S1.S0.I3)


Logic Circuit Design using Multiplexer

Advantages No need for logic simplification Minimize the IC package count Simplify the logic design


Logic Design using MUX

Case 1: Number of inputs is equal to number of select linesDesign procedure

Identify the decimal number corresponding to each minterm in the expression

Connect logic 1 level to input lines corresponding to these numbers

Connect logic 0 level to the others Connect inputs to selected lines


a three-variable function using a 8-to-1-line multiplexer

Case1: Inputs = Select lines


f(x,y,z) = m(0,2,3,5) using 8-to-1-line multiplexer

Example



Case 2: Number of inputs is higher than number of select linesProcedure 2.1: Reduce the number of inputs to the number of select lines by• inspection• k-map


Case 2

-Truth table of a 3 variable logic circuit

Input Output

x y z Y

0 0 0 f0

0 1 0 f2

1 0 0 f4

1 1 0 f6

Input Output

x y z Y

0 0 1 f1

0 1 1 f3

1 0 1 f5

1 1 1 f7


a 3-variable Boolean function using a 4-to-1-line multiplexer

Case2.1: Reducing Inputs


f(x,y,z) = m(0,2,3,5) using a 4-to-1-line multiplexer

Example


Reducing Inputs with K-map


f(x,y,z) = m(0,2,3,5)

Example


(a) Applying input variables y and z to the S1 and S0 select lines. (b) Applying input variables x and y to the S0 and S1 select lines.

More on Reducing Inputs


f(x,y,z) = m(0,2,3,5)(a) Applying input variables y and z to the S1 and S0 select lines. (b) Applying input variables x and y to the S0 and S1 select lines.

Example


Reducing 4-input to 3-input


f(w,x,y,z) = m(0,1,5,6,7,9,12,15)

Example



Procedure 2.2: Use multiplexer treewhen number of inputs exceeds the largest number of inputs on available ICs

Can be done by one of these two techniques- connect the MSB input to the enable/strobe

input- connect the MSB input to another

multiplexer


Demultiplexers/Decoders

-Performs the reverse operation of a multiplexer

Input lines are:

- 1 data line

- n select lines

- maybe 1 enable

Output lines are

- 2n output lines


A multiplexer/demultiplexer arrangement for information transmission

Application Example


Decoders

A n-to-2n-line decoder is a circuit that only one of the output line responds to the n-input data.

Number of input:output is n:2n

(Note: a demultiplexer is a decoder with an enable input acting as a data input line

A BCD to 7-segment decoder is a circuit that 7-bit output will make each segment of the 7-segment lit according to the 4-bit input


3-to-8-line Decoder


การใช้� 3-to-8-line decoder และ or-gate ในการสร�างวังจัร f1(x2,x1,x0) = m(1,2,4,5) และ f2(x2,x1,x0) = m(1,5,7)

Application Example


f1(x2,x1,x0) = m(0,1,3,4,5,6)

= m(2,7) and f2(x2,x1,x0) = m(1,2,3,4,6)

= m(0,5,7)

Application Example


f1(x2,x1,x0) = M(0,1,3,5) and f2(x2,x1,x0) = M(1,3,6,7)

(a) Using output or-gates. (b) Using output nor-gates.

Application Example


3-to-8-line decoder using nand-gates


f1(x2,x1,x0) = m(0,2,6,7) and f2(x2,x1,x0) = m(3,5,6,7) (a) Using output and-gates. (b) Using output nand-gates.

Application Example


And-gate 2-to-4-line decoder with an enable input

Decoder with Enable Input


Encoders

- Similar to decoders- Usually number of input lines are more than number of output linesNumber of input:output is 2n:n


Binary Adders

Binary Half-Adder Binary Full-Adder

xi yi si ci

0 0 0 0 0 1 1 0 1 0 1 0 1 1 0 1

xi yi ci-1 si ci

0 0 0 0 0 0 0 1 1 0 0 1 0 1 0 0 1 1 0 1 1 0 0 1 0 1 0 1 0 1 1 1 0 0 1 1 1 1 1 1


Binary Full-Adder

si = xi'.yi'.ci+xi'.yi.ci'+xi.yi'.ci'+xi.yi.ci

ci+1 = xi.yi + xi.ci + yi.ci


Parallel Binary Adder

Parallel (ripple) binary adder


Binary Subtractor

Binary Half-Subtractor Binary Full-Subtractor

xi yi di bi+1

0 0 0 0 0 1 1 1 1 0 1 0 1 1 0 0

xi yi bi di bi+1

0 0 0 0 0 0 0 1 1 1 0 1 0 1 1 0 1 1 0 1 1 0 0 1 0 1 0 1 0 0 1 1 0 0 0 1 1 1 1 1


Parallel Binary Subtractor

Parallel (ripple) binary subtractor


Parallel Binary Adder/Subtractor


Carry Look-ahead Adder

From Boolean expression of the F.A.ci+1 = xiyi + (xi+yi)ci

Let’s gi = xiyi (carry-generate function)and pi = (xi+yi) (carry-propagate function)c1 = g0 + p0c0

c2 = g1 + p1c1

= g1 + p1(g0 + p0c0)= g1 + p1g0 + p1p0c0


Carry Look-ahead Adder (cont.)

c3 = g2 + p2c2

= g2 + p2(g1 + p1g0 + p1p0c0)= g2 + p2g1 + p2p1g0 + p2p1p0c0

...

ci+1 = gi + pigi-1 + pipi-1gi-2 + ... + pipi-1...p1g0 + pipi-1...p0c0


Carry Look-ahead Adder (cont.)


BCD Arithmetic

BCD Adder Using a 4-bit binary adder to perform two one digit BCD addition

a decimal 6 (binary 0 1 1 0) will be added to the result if the sum output is an invalid BCD or if a carry at the MSB is 1

each BCD adder can be cascaded for adding several BCD digits


BCD Arithmetic

BCD Subtractor Convert the subtrahend to its 9’s complement form

Add the result to the minuend If the summation result is an invalid BCD code or if the carry from the MSB is 1, add decimal 6 (binary 0 1 1 0) and the end around carry (EAC) to this sum

If the summation result is a valid BCD code, the result is negative and in the 9’s complement form


Nine’s Complementer Circuit

A 9’s complementer circuit is a circuit designed to convert a decimal digit (in BCD code) to its 9’s complement

created by adding binary 1 0 1 0 to the 1’s complement of the number (ignore the carry)

(Proof is left as a student exercise)


Arithmetic Logic Unit (ALU)

• performs arithmetic and logic operations (depends on the selected mode)

• Read details and example in section 6.6


Comparators

A comparator is a circuit that compares the magnitudes of two binary numbersInput: Ai, Bi, Gi, Ei, Li

Gi= 1 when Ai-1Ai-2...A1A0 > Bi-1Bi-2...B1B0

Ei= 1 when Ai-1Ai-2...A1A0 = Bi-1Bi-2...B1B0

Li= 1 when Ai-1Ai-2...A1A0 < Bi-1Bi-2...B1B0 Output: Gi+1, Ei+1, Li+1

Gi+1= 1 when AiAi-1...A1A0 > BiBi-1...B1B0

Ei+1= 1 when AiAi-1...A1A0 = BiBi-1...B1B0

Li+1= 1 when AiAi-1...A1A0 < BiBi-1...B1B0


1-bit Comparator


Other MSI Circuits

• Parity generators/checkers• Code converters

BCD-to-binary converter Binary-to-BCD converter

• Priority encoders Decimal-to-BCD encoder Octal-to-binary Encoder

• Decoder/drivers for display devices BCD-to-decimal decoder/driver BCD-to-7-segment decoder/driver

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