Understanding flip flops, Cheat Sheet of Electronics

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SEQUENTIAL CIRCUITS I

LATCHES & FLIP FLOPS

2

Introduction

There are two types of sequential circuits:

 synchronous : outputs change only at specific time  asynchronous : outputs change at any time

 Multivibrator : a class of sequential circuits. They

can be:  Bistable (2 stable states)  Monostable or one-shot (1 stable state)  Astable (no stable state)

Bistable logic devices: latches and flip-flops.

 Latches and flip-flops differ in the method used

for changing their state.

CS1104- 11 Memory Elements 4 Memory Elements

 Memory element : a device which can remember

value indefinitely, or change value on command from its inputs. command Memory element stored value Q Q(t) : current state Q(t+1) or Q + : next state

Flip-Flop Vs. Latch

• The flip-flop’s CLOCK input is edge sensitive, meaning the flip-flop’s output changes on the edge (rising or falling) of the CLOCK input.
• The latch’s EN input is level sensitive, meaning the latch’s output changes on the level (high or low) of the EN input. 5

Combinational Logic

• Combinational Logic:
• Output depends only on current input
• Has no memory 2023/2/20 Sequential Circuits PJF - 7

Sequential Logic

• Sequential Logic:
  • Output depends not only on current input but also on past input values, e.g., design a counter
  • Need some type of memory to remember the past input values 2023/2/20 Sequential Circuits PJF - 8

Sequential Circuits

2023/2/20 Sequential Circuits PJF - 10 Circuits that we have learned so far Information Storing Circuits Timed “States”

Sequential Logic: Concept

• Sequential Logic circuits remember past inputs and past circuit state.
• Outputs from the system are “fed back” as new inputs - With gate delay and wire delay
• The storage elements are circuits that are capable of storing binary information: memory. 2023/2/20 Sequential Circuits PJF - 11

• A flip-flop in digital electronics is a circuit with two stable states that can be used to store binary data. The stored data can be changed by applying varying inputs.
• Flip-flops and latches are fundamental building blocks of digital electronics systems used in computers , communications , and many other types of systems.
• Both are used as data storage elements.

BASIC FF-SR – LATCH (NOR AND NAND LATCHES).

Applications of Flip-Flops: These are the various types of flip-flops being used in digital electronic circuits and the applications of Flip-flops are as specified below.

• Counters
• Frequency Dividers
• Shift Registers
• Storage Registers
• Bounce elimination switch
• Data storage
• Data transfer
• Latch
• Registers
• Memory

SR FLIP FLOP The SR-flip flop is built with two AND gates and a basic NOR flip flop. The o/ps of the two AND gates remain at 0 as long as the CLK pulse is 0, irrespective of the S and R i/p values. When the CLK pulse is 1, information from the S and R inputs permits through the basic FF. When S=R=1, the clock pulse occurrence roots both the o/ps go to 0. When the CLK pulse is detached, the state of the FF is unstated.