The document is a presentation on different types of counters in digital electronics, including synchronous, asynchronous, decade, up/down, ring, and Johnson counters. It describes binary-coded decimal (BCD) encoding, its advantages for decimal calculations, and drawbacks related to complexity and space efficiency. Additionally, it covers the operation and initialization of ring and Johnson counters, with supporting schematic diagrams and examples.

1. A Presentation on :
By-
MOHD BILAL
B.Tech (C.S.) II yr.

3. 2. Synchronous counter – all state bits change under control
of a single clock
Types of Counters
1. Asynchronous (ripple) counter – changing state bits are
used as clocks to subsequent state flip-flops
3. Decade counter – counts through ten states per stage
4. Up/down counter – counts both up and down, under
command of a control input
5. Ring counter – formed by a shift register with feedback
connection in a ring
6. Johnson counter – a twisted ring counter
7. Cascaded counter

5.  In computing and electronic systems, binary-coded
decimal (BCD) (sometimes called natural binary-
coded decimal, NBCD) or, in its most common
modern implementation, packed decimal, is an
encoding for decimal numbers in which each digit is
represented by its own binary sequence. Its main
virtue is that it allows easy conversion to decimal digits
for printing or display, and allows faster decimal
calculations.
 In BCD, a digit is usually represented by four bits
which, in general, represent the decimal digits 0
through 9. Other bit combinations are sometimes used
for a sign or for other indications (e.g., error or
overflow).
BCD CounterBCD Counter

6. • To encode a decimal number using the common BCD
encoding, each decimal digit is stored in a 4-bit nibble:
• Decimal: 0 1 2 3 4 5 6 7 8 9
• BCD : 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001
• Thus, the BCD encoding for the number 127 would be:
0001 0010 0111
Basics for BCDBasics for BCD

7. A Schematic diagram of BCD Counter

8.  Its drawbacks are a small increase in the
complexity of circuits needed to implement
mathematical operations.
 Uncompressed BCD is also a relatively
inefficient encoding—it occupies more
space than a purely binary representation.
Drawbacks

9.  Ring counters are implemented using shift
registers. It is essentially a circulating shift register
connected so that the last flip-flop shifts its value
into the first flip-flop. There is usually only a single 1
circulating in the register, as long as clock pulses
are applied.

10. Start control signal, which presets the
left-most flip-flop to 1 and clears the
others to 0.
An n-bit Ring Counter

12. The Johnson counter, also known as the
twisted-ring counter, is exactly the same as
the ring counter except that the inverted
output of the last flip-flop is connected to the
input of the first flip-flop.
Let’s say, starts from 000, 100, 110, 111, 011
and 001, and the sequence is repeated so
long as there is input pulse.

13. A Schematic diagram of JOHNSON
Counter

14. Clock Pulse No FFA FFB FFC FFD
0 0 0 0 0
1 1 0 0 0
2 1 1 0 0
3 1 1 1 0
4 1 1 1 1
5 0 1 1 1
6 0 0 1 1
7 0 0 0 1
Truth Table for JOHNSON
Counter

15. To initialize the operation of the Johnson counter, it
is necessary to reset all flip-flops, as shown in the
figure. Observe that neither the Johnson nor the ring
counter will generate the desired counting sequence
if not initialized properly.

16. • Digital Electronics BookDigital Electronics Book
• Net Surfing :-Net Surfing :-
• http://www.electronics-tutorials.ws
• http://www.doc.ic.ac.uk/~nd/surprise_96/journal/v
ol4/cwl3/report.html#bcd