Digital Circuit Design - Lecture 2 pptx

 A more descriptive term might be feedforward combinational logic circuits.. These are circuits in which there is no feedback.. depends not only on its current inputs, but also on the

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Sequential Design Basics

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Lecture 2 topics

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Digital Circuit Types

outputs depend only on its current inputs.

 A more descriptive term might be feedforward

combinational logic circuits These are circuits in which there is no feedback.

depends not only on its current inputs, but

also on the past sequence of inputs

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State changes

times specified by a clock

 Clock frequency C f = 1 / T

 Where T is the Clock period

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Sequential elements are bistable

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S-R Latch

elements Formed from a pair cross

connected pair of NOR gates.

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The D Latch

CMOS design.

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Timing diagram for a D Latch

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The D F/F

negative edge triggered

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Timing for a D Flip-Flop

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D F/F Behavior

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D F/F with Preset and Clear

initialization.

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Scan Chains

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Scan Chains

 Can use scan chains to

inputs data or extract

data

D F/F

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The T Flip Flop

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R 0 0 1 1

S 0 1 0 1

Q Q 0 1 Not allowed CLK

Q Q Q CLK

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Q 0 1 CLK

K 0 1 0 1

Q Q 0 1 Q CLK

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A simple up down counter

 Start with state diagram

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K Maps for the toggle F/Fs

00 01 11 10 0

T1 = x’y2 + x y2’

= x xor y2

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Implementation

y2 y1

x

1

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