Flip Flops & Adder Circuits

D Type Flip Flops

Flip flops are electronic circuits used within a computer’s memory to store single bits in one of two states, either a 1 or a 0. Flip flops can alter the state from one to the other.

D type flip flops

There are several types of flip flop, but by far the most common are D type flip flops.
D type flip flops have two inputs:
- Data, D.
- A clock signal.
D type flip flops have one output, Q.

Clock signal

The clock signal is a regular and steady pulse used by a CPU to time operations.
The output Q of a D type flip flop can only be altered at the beginning of a clock signal.
A change to Q will only occur if D is in a different state to what it was at the start of the previous clock signal.
This happens regardless of whether or not there has been a change in between clock signals.

Signal diagram

The top line shows the data, D, alternating between 0 and 1 at random.
The middle line is the steady and regular pulse of the clock signal.
- The start of each pulse identified with an arrow.
The bottom line is the output, Q.

Process

At the first pulse, the output changes to ‘1’ to match D.
At the second pulse, D is still ‘1’ so Q doesn’t change.
At the third pulse, D is now ‘0’ so Q changes to ‘0’ at this point.
At the fourth pulse, D is back to ‘1’ so Q changes to match it.
- The change in D in between clock pulses is ignored.

Adder Circuits

Adder circuits are used by the Arithmetic Logic Unit (ALU) in a processor to perform the addition of two binary digits.

Types of adder circuit

Adder circuits come in two forms:
- Half adder circuits.
- Full adder circuits.

Half adder circuits

Half adder circuits accept two inputs and output both the result and a carry bit.
They make use of an XOR gate and an AND gate, laid out as shown.

Half adder table

The actions of the two gates can be displayed in a table as shown.
The output at S gives the 2⁰ binary digit.
The output at C gives the 2¹ binary digit (the carry bit).

Full adder circuits

Full adders have the same output as a Half Adder (the sum and a carry bit), but they accept three inputs (two bits plus a carry bit).
They are constructed from two Half Adders.

Full adder table

In a full adder:
- S = A XOR B XOR C(in)
- C(out) = (A AND B) OR (C(in) AND (A XOR B))

1Components of a Computer

1.1Structure & Function of the Processor

1.1.1Structure of the CPU

1.1.2Fetch, Decode, Execute Cycle

1.1.3Factors Affecting CPU Performance

1.1.4CPU Architecture

1.2Types of Processors

1.2.1CISC & RISC

1.2.2Multicore & Parallel Cores

1.3Input, Output & Storage

1.3.1Computer Systems

1.3.2Magnetic Storage

1.3.3Optical Storage

1.3.4Types of Optical Storage

1.3.5Types of Memory

1.3.6Flash Memory

1.3.7Virtual Memory

2Software & Software Development

3Exchanging Data

4Data Types, Data Structures & Algorithms

4.1Data Types

4.1.1Data Types

4.1.2Arrays & Strings

4.1.3Representing Numbers

4.1.4Binary Arithmetic

4.1.5Hexadecimal

4.1.6Converting Binary Numbers

4.1.7Floating Points in Binary

4.1.8Floating Point Arithmetic

4.1.9Bitwise Manipulation

4.1.10Character Sets

4.2Data Structures

4.2.1Arrays, Linked Lists & Queues

4.2.2Graphs, Hash Tables & Stacks

4.2.3Trees

4.3Boolean Algebra

4.3.1Computational Logic

4.3.2Boolean Logic

4.3.3Karnaugh Maps

4.3.4Boolean Identities

4.3.5Flip Flops & Adder Circuits

5Legal, Moral, Cultural & Ethical Issues

5.1Computing Related Legislation

5.1.1Data Protection Act (1998)

5.1.2Computer Misuse Act (1990)

5.1.3Copyright Designs and Patents Act (1988)

5.1.4Regulation of Investigatory Powers Act (2000)

5.2Moral & Ethical Issues

5.2.1Online Activity Tracking

5.2.2Censorship

5.2.3Cultural Issues

5.2.4Environmental Issues

5.2.5Layout, Colour Paradigms & Character Sets

6Elements of Computational Thinking

6.1Thinking Abstractly

6.1.1Abstraction

6.2Thinking Procedurally

6.2.1Decomposition

6.3Thinking Logically

6.3.1Pseudocode & Flow Diagrams

7Problem Solving & Programming

7.1Programming Techniques

7.1.1Programming Fundamentals

7.1.2Modularity

7.2Programming Construction

7.2.1Integrated Development Environments

7.2.2Testing

8Algorithms

8.1Algorithms

8.1.1Interpreting, Correcting & Completing Algorithm

8.1.2Sort Algorithms

8.1.3Insertion & Merge Sort

8.1.4Search Algorithms

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