1. Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
Sequential Logic
Post-Activity Discussion: An Overview
Digital Electronics
© 2014 Project Lead The Way, Inc.
Project Lead The Way, Inc.
Copyright 2009

2. Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
This presentation will
Introduce the basics of combinational and sequential logic.
Present the logic symbol and function table for the “D” flip-flop.
Review the design for a simple sequential logic circuit.
Introductory Slide / Overview of Presentation
Project Lead The Way, Inc.
Copyright 2009

3. Combinational & Sequential Logic
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
Combinational
Logic Gates
Inputs
Outputs .
Combinational
Logic
Sequential
Logic
Combinational
Logic Gates .
Inputs
Outputs
Memory Elements
(Flip-Flops)
Clock
Combinational Logic has one or more inputs and one or more outputs. The outputs are a function of the present value of the inputs.
Sequential logic can also have one or more inputs and one or more outputs. However, the outputs are a function of both the present value of the inputs and also the previous output values. Thus, sequential logic requires memory to store previous outputs values.
Project Lead The Way, Inc.
Copyright 2009

4. Sequential Logic - An Overview
The “D” Flip-Flop
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital Q
Preset
Data-In
Clock
Clear
Inputs
Outputs
Preset
Clear
Clock
Data-In 1 
: Rising Edge of Clock
The output will stay the same. X
ILLEGAL CONDITION
The basics of the D flip-flop.
Project Lead The Way, Inc.
Copyright 2009

5. Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
The “D” flip-flop is just one of several types of flip-flops that can be used to implement sequential logic designs.
This presentation will look at the Divide-by-Two circuit.
This sample flip-flop application can be implemented with “D” flip-flops. Unit 3 of this course will spend a significant amount of time exploring other flip-flops and their applications.
The purpose of this introduction is to provide a basis of understanding for the sequential logic subsection of the Board Game Counter design.
A brief overview of sequential logic and why it is being introduced at this point.
Project Lead The Way, Inc.
Copyright 2009

6. Divide-by-Two Circuit: 1st Clock
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
Preset = 1
Pulse-Out
Pulse-In
Logic ‘0’
Logic ‘1’
Clear = 1
Analysis of a Divide-by-Two circuit (1st Clock Pulse).
Pulse-Out
Pulse-In
Preset = 1
Clear = 1
Project Lead The Way, Inc.
Copyright 2009

7. Divide-by-Two Circuit: 2nd Clock
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
Preset = 1
Pulse-Out
Pulse-In
Logic ‘0’
Logic ‘1’
Clear = 1
Analysis of a Divide-by-Two circuit (2nd Clock Pulse).
Pulse-Out
Pulse-In
Preset = 1
Clear = 1
Project Lead The Way, Inc.
Copyright 2009

8. Divide-by-Two Circuit: 3rd Clock
Sequential Logic - An Overview
Divide-by-Two Circuit: 3rd Clock
Digital Electronics TM
1.3 Introduction to Digital
Preset = 1
Pulse-Out
Pulse-In
Logic ‘0’
Logic ‘1’
Clear = 1
Analysis of a Divide-by-Two circuit (3rd Clock Pulse).
Pulse-Out
Pulse-In
The 3rd pulse is a repeat of the 1st, the 4th will be a repeat of the 2nd, etc.
Preset = 1
Clear = 1
Project Lead The Way, Inc.
Copyright 2009

9. Divide-by-Two Circuit Period & Frequency - Overview
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
The period of Pulse-Out is twice the period of Pulse-In.
Since the period is twice, the frequency is divided in half.
Thus, this is a
Divide-by-Two circuit.
Preset
Pulse-In
Clear
Pulse-Out
Complete waveform for the Divide-by-Two Circuit.
Pulse-Out
Pulse-In
Preset
Clear
Project Lead The Way, Inc.
Copyright 2009

10. Divide-by-Two Circuit Period & Frequency – The Numbers
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
Pulse-Out
Pulse-In T1 T2
Detailed view of the period & frequency of the input/output signals for the Divide-by-Two circuit.
Pulse-Out
Pulse-In
Preset
Clear
Project Lead The Way, Inc.
Copyright 2009

11. Divide-by-Two Circuit Preset & Clear
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
Preset
Pulse-In
Clear
Pulse-Out
Detailed view of the CLEAR & PRESET inputs and their effect on the output waveform.
Pulse-Out
Pulse-In
Preset & Clear are active low signals.
Preset
preset holds the output high
Clear
clear holds
the output low
Project Lead The Way, Inc.
Copyright 2009

12. Sequential Logic Design Example
Sequential Logic - An Overview
Sequential Logic Design Example
Digital Electronics TM
1.3 Introduction to Digital
The following is a review of the design and operation of a sequential logic circuit using “D” flip-flops. This design is a simple two-bit binary counter that counts from zero (010=002) to three (310=112) and then repeats.
Specifications for an simple sequential logic design.
Project Lead The Way, Inc.
Copyright 2009

13. Design Example: Circuit Design
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
Zero-to-Three Counter circuit diagram or schematic.
Note: This is the first time the students will have seen the CLOCK_VOLTAGE component. Be sure to explain what it is.
Project Lead The Way, Inc.
Copyright 2009

14. Design Example: Functional Test (1 of 3)
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
THE FIRST FLIP-FLOP IS CLOCKED BY CLOCK-IN.
Step-by-step analysis (functional test) of the Zero-to-Three Counter.
B IS HALF THE FREQUENCY OF CLOCK-IN. A B
Clock-In
Project Lead The Way, Inc.
Copyright 2009

15. Design Example: Functional Test (2 of 3)
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
The second flip-flop is clocked by the of the first flip-flop.
A is half the frequency of B.
Note: A toggles on the falling edge of B, which is the rising edge of .
Step-by-step analysis (functional test) of the Zero-to-Three Counter. A B
Clock-In
Project Lead The Way, Inc.
Copyright 2009

16. Design Example: Functional Test (3 of 3)
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
“0”
“1” 1
“2” 1
“3” 1
“0”
Step-by-step analysis (functional test) of the Zero-to-Three Counter. A B
Clock-In
Project Lead The Way, Inc.
Copyright 2009

17. Design Example: IC Component View
Sequential Logic - An Overview
Digital Electronics TM
1.3 Introduction to Digital
This slide shows how the gates are actually part of integrated circuits. This connection diagram was taken directly from a manufacturer datasheet for the flip-flop. In this case both flip-flops happen to be in the same IC package. 3 2 1 4 5 6 11 12 13 10 9 8
Project Lead The Way, Inc.
Copyright 2009