BRANCH-E&TC ENGINEERING

SEM – 3Rd

SUBJECT-DIGITAL ELECTRONICS

CHAPTER-04- register Memory & PLD

TOPIC- counters

Ay-2021-2022 ,winter-2021

FACULTY-ER S MOHANTA.(Hod e & tc engg Dept)

Presentation On:-

COUNTERS

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OVERVIEW OF COUNTERS

• Common tasks of counter
• Count up or down
• Increment or decrement count
• Sequence events
• Divide frequency
• Address memory
• As memory

• Counter-by definition
• One input (clock)
• Outputs follow defined sequence

CHARACTERISTICS OF COUNTERS

• Number of bits (4-bit, 8-bit, etc.)
• Maximum count
• 4 bit = 2⁴ = 0000 to 1111 in binary
• 8 bit = 2⁸ = 0000 0000 to 1111 1111 in binary
• Modulus of counter-number of states
• Decade counter
• 4-bit
• 8-bit
• Up or down counter
• Asynchronous or synchronous counter
• Presettable counter
• Self-stopping counter

RIPPLE COUNTER

0 0 0 0

0 0 0 1

Binary Output

0 0 1 0

0 0 1 1

0 1 0 0

0 1 0 1

0 1 1 0

0 1 1 1

1 0 0 0

Pulse 1

Clock Input

All J-K flip-flops

in the

TOGGLE MODE

PS and CLR input

are

INACTIVE

Pulse 2

Pulse 3

Pulse 4

Pulse 5

Pulse 6

Pulse 7

Pulse 8

On the next clock pulse (8) all FFs

will toggle because each will receive

a H-to-L pulse- one after another.

Watch the count ripple thru the counter.

This 4-bit counter has 16 states and

will count from binary 0000 through 1111

and then reset back to 0000.

The counter has a modulus of 16.

RIPPLE COUNTER WITH WAVEFORMS

0 0 0 0

0 0 0 1

Binary Output

0 0 1 0

0 0 1 1

0 1 0 0

0 1 0 1

Pulse 1

Clock Input

Pulse 2

Pulse 3

Pulse 4

Pulse 5

FFs triggered on

H-to-L pulse.

CLK toggles 1s FF.

1s FF toggles 2s FF.

2s FF toggles 4s FF.

DECADE COUNTER

Binary Output

0 1 1 1

1 0 0 0

Pulse 1

Clock Input

Pulse 2

Pulse 3

Pulse 4

Pulse 5

Pulse 6

Pulse 7

Pulse 8

To change mod-16 counter to decade counter:

Reset count to 0000 after 1001 (9) count.

When count hits 1010 reset to 0000.

See added 2-input NAND gate that clears all

JK FFs to 0 when count hits 1010.

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1 0 0 1

0 0 0 0

0 0 0 1

0 0 1 0

0 0 1 1

0 1 0 0

0 1 0 1

Count is at 1001.

Next clock pulse will increment counter for a

short time to 1010 which will activate the NAND gate

and reset the counter to 0000.

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Initial count at 0111

All J & K inputs = 1

All PR inputs = 1

DOWN COUNTER

Changes from Ripple Up Counter are

wiring from Q’ outputs (instead of Q outputs)

to the CLK input of the next FF.

Pulse 1

Pulse 2

1 1 1

1 1 0

Initial count

set at

binary 111

1 0 1

Pulse 3

Pulse 4

1 0 0

0 1 1

Pulse 5

0 1 0

SELF-STOPPING DOWN COUNTER

Pulse 1

Pulse 2

Pulse 3

Pulse 4

Pulse 5

1 1 1

1 1 0

1 0 1

1 0 0

0 1 1

0 1 0

This is a 3-bit down counter.

The 1s FF is in TOGGLE mode when counting (J & K = 1).

The 1s FF switches to HOLD mode when the J and K inputs are forced LOW by the OR gate

when the count decrements to 000. The count stops at 000.

0 0 1

Pulse 6

0 0 0

Pulse 7

Pulse 8

Watch count on

Pulse 8.

The count remained

at binary 000.

COUNTER USED FOR FREQUENCY DIVISION

800 Hz

÷ 2

÷ 4

÷ 8

÷ 16

USING THE 7493 COUNTER IC

• Counters are available in IC form.
• Either ripple (7493 IC) or synchronous (74192 IC) counters are available.

7493 Counter IC

wired as a 4-bit

binary counter

1600 Hz

MAGNITUDE COMPARATOR

A magnitude comparator is a combinational logic device that compares the value of two binary numbers and responds with one of three outputs (A=B or A>B or A<B).

Input binary 0001

Input binary 1100

HIGH

HIGH

Input binary 1111

Input binary 0110

Input binary 0111

Input binary 0111

HIGH

TROUBLESHOOTING EQUIPMENT

• Logic Probe
• Logic Pulser
• Logic Clip (logic monitor)
• Digital IC Tester
• DMM/Logic Probe
• DMM or VOM
• Dual-trace Oscilloscope
• Logic Analyzer

SIMPLE TROUBLESHOOTING HINTS

• Feel top of IC to determine if it is hot
• Look for broken connections, signs of excessive heat
• Smell for overheating
• Check power source
• Trace path of logic through circuit
• Know the normal operation of the circuit

Thank You