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Counters Photon Counting Chip (PCC) Picture of fuse using PCC Interest The Difference Engine (1872) was a general purpose mechanical calculator solving mathematical problems with up to 31 digit places of accuracy. Through the use of punch-cards, the Analytical Engine could be programmed

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Counters l.jpg
Counters

Photon Counting Chip (PCC)

Picture of fuse using PCC

CENT-113 Digital Electronics


Interest l.jpg
Interest

  • The Difference Engine (1872) was a general purpose mechanical calculator solving mathematical problems with up to 31 digit places of accuracy.

  • Through the use of punch-cards, the Analytical Engine could be programmed

CENT-113 Digital Electronics


Counters general information l.jpg
Counters General Information

  • Purpose: Counting events or periods of time or putting events in sequence.

  • Other functions: Dividing frequency, addressing, and serving as memory units.

  • Flip-Flops are wired together forming circuits that count.

  • Self contained counters in ICs are available in TTL and CMOS.

CENT-113 Digital Electronics


Ripple counters l.jpg
Ripple Counters

  • 4-bit counter: D-C-B-A=8s-4s-2s-1s

    • 8s: Most Significant Digit/Bit (MSD/B)

    • 1s: Least Significant Digit/Bit (LSD/B)

    • BCD count from 0000 to 1111 (Decimal 0-15)

    • Need a counter with 16 different output states

      • Mod-16 counter: Modulus of the mod-16 counter undergoes 16 different states to complete the counting cycle.

      • Mod-16 counter uses 4 J-K flip-flops

CENT-113 Digital Electronics


Mod 16 ripple counter l.jpg

D

C

B

A

1

1

1

1

Q

Q

Q

Q

J

J

J

J

FF2

FF1

FF4

FF3

CLK

CLK

CLK

CLK

1

1

1

1

K

K

K

K

Mod-16 Ripple Counter

Clock Pulses

BinaryOutput

3

2

4

1

Input

Note: The clock triggers only FF1

-Mode 16 means the counter has 16 states.

-A ripple counter causes a chain reaction

change of FF states.

-asynchronous counter means that all FFs

do not trigger at The same time.

-4 bit counters have 4 binary outputs.

10

6

5

7

9

1

2

8

4

3

CLK

FF1 Q

FF2 Q

FF3 Q

FF4 Q

CENT-113 Digital Electronics


Mod 10 ripple counter l.jpg

1

1

1

Q

Q

Q

J

J

J

J

FF3

FF2

FF4

FF1

CLK

CLK

CLK

1

1

1

Mod-10 Ripple Counter

  • The counting sequence is 0000 to 1001 (0-9).

  • It has 4 places 8s, 4s, 2s, 1s

  • NAND gate clears all FF to 0 after the 1001 (9) count.

  • Also called a decade (meaning 10) counter.

Clock

Pulses

1

D

C

B

A

Q

CLK

K

K

K

K

1

CLR

CLR

CLR

CLR

CENT-113 Digital Electronics


Synchronous counters l.jpg
Synchronous Counters

  • A synchronous counter eliminates the accumulated propagation delay of the ripple counter by tying all clock inputs to a common clock signal.

  • In a synchronous counter each flip-flop must not be allowed to toggle until all flip-flops that precede it are high (set).

  • The J-K inputs are tied to an AND gate that ANDs the Q outputs from all previous flip-flops.

  • Synchronous counters can be used to form any modulus counter by using a NAND gate to reset all the flip-flops. The inputs to the logic gate are from the Q outputs of the flip-flops that form the binary representation of the MOD numbers.

  • Synchronous counters can be used as down counters by taking the output from the Q rather than the Q of each flip-flop.

  • Synchronous counters can be used in many of the same design applications as ripple counters.

CENT-113 Digital Electronics


3 bit mod 8 synchronous counter l.jpg

1

Q

Q

J

J

J

FF3

FF2

FF1

CLK

CLK

1

K

K

3 Bit Mod 8 Synchronous Counter

Clock inputs are connected in parallel.

Used in high frequency operations.

J-K FFs used in toggle or hold modes.

Toggle: J=1, K=1 Hold J=0, K=0

C

B

A

Q

CLK

Clock

Pulses

K

Truth Table

CENT-113 Digital Electronics


Questions l.jpg
Questions

  • Q. What does it mean to be a 3 bit counter?

  • A. The maximum binary output is 111.

  • Q. What does it mean to be a Mod-7 counter?

  • A. There are seven unique counting states in the particular counter.

  • Q. What is the difference between a synchronous & an asynchronous counter when they both use clock inputs?

  • A. Most synchronous counters have parallel clocks.

CENT-113 Digital Electronics


3 bit ripple down counter l.jpg

1

1

1

Q

Q

Q

J

J

J

FF1

FF2

FF3

CLK

CLK

CLK

1

1

1

K

K

K

Q

Q

Q

3 Bit Ripple Down Counter

Preset

Note: A counter that counts

higher to lower is called a

down counter. It recirculates

& goes back to 0111.

PS

C

B

A

PS

PS

Clock Pulses

Truth Table

CENT-113 Digital Electronics


Self stopping counter l.jpg

1

1

Q

Q

J

J

J

FF3

FF1

FF2

CLK

CLK

1

1

K

K

Q

Q

Q

Self-Stopping Counter

  • Up and down counters can be stopped by using a logic gate. The inputs to J & K at FF1 stops counter and places it in a hold, stopping count at 000.

Preset

PS

C

B

A

Q

PS

PS

Clock Pulses

CLK

K

CENT-113 Digital Electronics


Counters as frequency dividers l.jpg
Counters as Frequency Dividers

1 Second Timing Circuit

  • Counters are used for frequency division.

  • Uses: Digital clocks & watches, oscilloscopes, and television receivers.

  • A decade counter can be used as a divide by 10 counter. If a decade counter was used along with a mod-6 counter, the divide by 60 circuit would be designed.

Divide by

60 circuit

60 HZ

1 HZ ( 1 pulse per second)

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Ttl counters l.jpg
TTL Counters

  • 7493 *182

CENT-113 Digital Electronics


Synchronous up down counter ics l.jpg
Synchronous Up/Down-Counter ICs

  • The 74192 is a BCD decade up/down synchronous counter.

  • The 74193 is a 4-bit binary up/down synchronous counter.

  • These chips have parallel data input leads used to preset the counter.

  • Two clock inputs are available. 1 UP count & another for a DOWN count.

  • A terminal count UP and a terminal count DOWN output signal can be used to cascade several ICs together.

  • Two additional synchronous IC counters are the 74190 and the 74191.

  • The 74190 is a BCD counter and the 74191 is a 4-bit binary counter.

  • These chips have a terminal count output and an enable input. With these two connections, cascaded ICs held-off until the proper count. This means that the entire counter can be synchronous.

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Cmos counters l.jpg
CMOS Counters

  • 74HC393

  • 74HC193

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74hc393 wired as 4 bit binary counter l.jpg
74HC393 wired as 4-bit Binary Counter

  • Two 4-bit binary ripple counters, each counter has 4 T-FFs

  • MR input is an asynchronous master rest pin.

  • Triggered High to low.

  • Counts 0000 to 1111.

Q3

8s

4s

2s

1s

Q2

Clock

Pulses

Q1

Q0

CLK

Counter

74HC393

Reset

MR

Clear=1

Count=0

CENT-113 Digital Electronics


74hc193 wired as mod 6 counter l.jpg

PL activates the synchronous parallel load

with a low just after the highest count of

Binary 0110.

+5V disables the CPD & ground disables MR.

PL

74HC193 wired as Mod-6 Counter

  • 74HC193 is a presettable synchronous 4-bit binary up/down counter IC

  • Clock edge triggered low to high.

  • Modes of operation: reset, parallel load, count up, count down

Q3

8s

4s

2s

1s

Q2

Q1

A

Q0

Counter

74HC193

B

C

D

+5V

Clock

Pulses

CPD

Count Down

CPU

Count Up

MR

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Counting system using optical encoder l.jpg
Counting System using Optical Encoder

+5V

+5V

+5V

+5V

1

Optoisolator

4N25

4

Common

Anode

LED 1

+5V

Decade

Counter

74193

Decoder/Driver

7447

Count

Up

7414

2

2N3904NPN

3

CLR

GND

GND

CENT-113 Digital Electronics


74hc85 comparator ic l.jpg
74HC85 Comparator IC

  • The 74HC/HCT85 are high-speed CMOS devices and are pin compatible with low power Schottky TTL (LSTTL).

  • The 74HC/HCT85 are 4-bit magnitude comparators that can be expanded to almost any length. They perform comparison of two 4-bit binary, BCD or other monotonic codes and present the three possible magnitude results at the outputs (QA>B, QA=B and QA<B). The 4-bit inputs are weighted (A0 to A3 and B0 to B3), where A3 and B3 are the most significant bits.

CENT-113 Digital Electronics


74hc85 comparator ic continued l.jpg

L= Low logic level

H= High logic level

X= Don’t care

74HC85 Comparator IC Continued

Pin Diagram

Truth Diagram

Data Inputs

A3

B2

A2

A1

B1

A0

B0

Vcc

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

A>B

A=B

A<B

A>B

A=B

A<B

B3

GND

Data

Input

Cascade

Inputs

Outputs

-Two 4-bit comparators can be cascaded

to compare 8 bit numbers or words.

-Cascading means joined to another.

CENT-113 Digital Electronics


Sequential logic troubleshooting tools l.jpg
Sequential Logic Troubleshooting Tools

  • Commercial Logic Probe (TTL/CMOS SS) & (MEM/PULSE SS) In MEM any signal (0 or 1) can pulse (as short as 50ns) will activate the pulse LED.

  • Digital Logic Pulser: Lets you generate a signal.

CENT-113 Digital Electronics


Sequential logic troubleshooting tools22 l.jpg
Sequential Logic Troubleshooting Tools

  • Logic monitors with IC clips check chips in circuits with each pin lit by LED.

  • Portable IC tester tests chips out of circuit.

  • Handheld Oscilloscope.

CENT-113 Digital Electronics


Troubleshooting a counter l.jpg
Troubleshooting a Counter

  • Use best tool.

  • Use 5 senses to troubleshoot.

  • Check powers supply and common.

  • Use logic monitor to observe counting operation.

  • Check reset.

  • Check bent pins

CENT-113 Digital Electronics


Conclusions l.jpg
Conclusions

  • A. What is the difference between a FF and a counting circuit?

  • Q. FFs are the building blocks for counting circuits.

CENT-113 Digital Electronics


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