Date: 01/12/2014 Asynchronous (Ripple) Counters Patel Siddhi P rd SEM Computer Science and Engneering B.M.C.E.T Subject Name: Digital Electronics Teacher Name: Ms.Henal Patel

Introduction – Counter Binary Ripple Counter Asynchronous (Ripple) Counters 2 – bit Ripple Binary Counter 3 – bit Ripple Binary Counter 4 – bit Ripple Binary Counter A Four - bit Asynchronous Up And Down Counters Asynchronous Up Counter Asynchronous Down Counter The Ripple Effect - Problem And Solution CONTENTS

Counters Counter: A Circuit used for counting the pulse is known as a counter Binary Counter Counter that follows a binary sequence N bit binary counter counts in binary from n to 2 n Applications: Watches Clocks Alarms

Two main types of counters Ripple (asynchronous) counters Synchronous counters Ripple Counters Flip flop output serves as a source for triggering other flip flops Ripple counters triggered by initial Count signal Ripple counters allow some flip-flop outputs to be used as a source of clock for other flip-flops. n flip-flops a MOD (modulus) 2n counter.

Binary Ripple Counter  Count signal toggles output of low-order flip flop Low-order flip flop provides trigger for adjacent flip flop Not all flops change value simultaneously Focus on D &T flip flops implementation Fig.1 (Binary Ripple Counter) Reference[1]

2-bit Ripple Binary Counter. Output of one flip-flop is connected to the clock input of the next more-significant flip-flop. Asynchronous (Ripple) Counters Fig.2 (2-bit Ripple Counter) Reference[1]

Asynchronous (Ripple) Counters 3-bit Ripple Binary Counter. Fig.3 (3-bit Ripple Counter) Reference[1]

Asynchronous (Ripple) Counters 4-bit Ripple Binary Counter. Fig.4 (4-bit Ripple Counter) Reference[1]

Each FF output drives the CLK input of the next FF. FFs do not change states in exact synchronism with the applied clock pulses. There is delay between the responses of successive FFs. Ripple counter due to the way the FFs respond one after another in a kind of rippling effect. Asynchronous Counters

A Four-bit Asynchronous Up And Down Counters Fig.5 (4- bit Up And Down Counter) Reference[1]

A Four-bit Up Counter Fig.6 (4-bit Up Counter) Reference[1]

A Four-bit Down Counter Fig.7 (4-bit Down Counter) Reference[1]

A Four-bit Up And Down Counters Fig.8 (4-bit Up And Down Counter) Reference[1]

The Ripple Effect… Fig.9 (Ripple Effect...) Reference[2]

Ripple Effect…The Problem Propagation delays in an asynchronous (ripple-clocked) binary counter. If the accumulated delay is greater than the clock pulse, some counter states may be misrepresented! Fig.10 (Ripple Effect-The Problem) Reference[2]

K JQ Q CLK CLR K JQ Q CLK CLR K JQ Q CLK CLR CBA BCBC All J, K inputs are 1 (HIGH). A B 12 C NAND Output Clock MOD-6 counter produced by clearing (a MOD-8 binary counter) when count of six (110) occurs. Example (cont’d): Ripple Effect…The Solution Fig.11 (The Solution of Ripple Effect) Reference[2]

A B C NAND Output Clock Temporary state Counter is a MOD-6 counter. Example : Counting sequence of circuit. Fig.12 (Example of Ripple Counter) Reference[2]

Reference [1] R. P. JAIN, ‘Modern Digital Electronics’, McGraw Hill Education, Fourth Edition [2] A.K Maini, ‘Digital Electronics: Principle and Circuits’, Wiley India Publication

CONCLUSION Counters serve many purposes in sequential logic design. There are lots of variations on the basic counter. Some can increment or decrement. An enable signal can be added. The counter’s value may be explicitly set.