Counter Application(Part B)

By : Pn Siti Nor Diana Ismail

CHAPTER 3

ii. Cascade Counter

It connected in cascade to achieve higher modulus operation

Last stage output of one counter derive input of next counter

Also used to divide high frequency clock signal

Example : 2-bit and 3-bit counter

Based on 2 cascaded counter given.- Asynchronous counter have positive edge-triggered

- all both JK input are high. So, output always toggle when clock triggered.

- initial condition are LOW.The final output modulus-8 counter (Q4)

occurs once for every 32 input clock pulse.So, it can be classified as divide-by-32

counter.Therefore, the overall modulus 4x8=32

When operating synchronous counter in cascaded configuration, it necessary to use count enable (CTEN) and terminal count (TC) function to achieve higher-modulus operation.

CTEN = G while TC = analog to ripple output (RCO).

(for some devices)

Example 1: A modulus-100 counter using cascaded decade counter

This modulus-100 counter operation is :-- TC output counter1 connect to CTEN input counter2.

- CTEN input on counter2 start from low until counter1 reach last or TC=high.

- When TC=high, it will enable counter2. in this case, when 1st clock pulse after counter1 reach TC(CLK10) counter2 goes from initial state to 2nd state.

- it will continuosly. Counter2 will complete one cycle after 100 clock pulses.- Since it decade counter, counter 1 must go through 10 complete cycles before counter 2 complete its 1st cycle.(Every 10 cycles of Counter 1, Counter 2 goes through 1 cycle). Counter 2 completes cycle after 100 clocks

- overall modulus of 2 cascaded counter;10 x 10 = 100

Example 2 :3 cascaded decade counter

Given basic clock frequency 1MHz to obtain 100kHz, 10kHz

and 1kHz by using cascaded counter. (as a frequency divider)

Also know as countdown chainsSolution:

series of cascade decade counter can be formed.

If 1MHz signal divide by 10, so output = 100kHz

If 100kHz divide by 10, so output = 10kHzIf 10kHz divide by 10, output = 1kHzSo, we can used 3 cascade decade counter

to produce 1kHz.

Example 3 Determine the overall modulus of the two cascaded counter for (a) and (b)

For (a) the overall modulus for the 3 counter configuration is 8 x 12 x 16 = 1536for (b) the overall modulus for the 4 counter configuration is 10 x 4 x 7 x 5 = 1400

Example 4 : A divide-by-100 counter using two 74LS160 decade counters.

Used 74162 decade counter to obtain 10kHz waveform 1MHz clock. Show a logic diagram.

Solution;

to obtain 10kHz from 1MHz is required a division factor of 100.

So, the 2 logic ICs (74LS162) should cascaded.

Exercise

Show with general blocks diagram how to achieve each of the following using a FF, a decade counter and 4-bit binary counter or any combination

a)Divide by 20 counterb)Divide by 32 counterc)Divide by 160 counterd)Divide by 320 counter

iii. Counter Decoding

It ‘s necessary that some state to be decoded

By using decoder or logic gatesTC is a single decoded state (the last state)

in counter sequence

Example 1: Decoding of state 6 (110).

To determine when the counter is in a certain states in its sequence by using decoders or logic gates.

Solution :

when Q2=1, Q1=1 and Q0=0, a High appears on output decoding gate indicate counter is at State6.

It call active-HIGH decoding.

If replace AND-Gates with NAND-Gates, it will provide active-LOW decoding.

Example 2

Implement the decoding of binary state2 and binary state7 of 3-bit synchronous counter. Show entire counter timing diagram and output waveform of decoding gates.

Binary state2 = Q2’ Q1 Q0’ = (010).Binary state7 = Q2 Q1 Q0 = (111).

A 3-bit counter with active-HIGH decoding of count2 and count7.

Solution :

Exercise

Show the logic for decoding state 5 in the 3-bit counter.

Decoding GlitchesPropagation delay due to ripple effect in

synchronous counter create transition state in which the counter output change at different times.

State produce voltage spike at short duration (glitches) on output decoder connect to counter.

Glitches problem also occurs to some degree with synchronous counter because propagation delay from clock to Q output each Flip-Flops.

- Outputs with glitches from the previous decoder. - Glitch widths are exaggerated for illustration and are usually only a few nanoseconds wide.

How to eliminate the GLITCHES?Delay cause false state at short duration.

Value of false binary state at each critical transition is indicate on diagram.

One ways to eliminate “glitches”,- is to enable the decode output at time after “glitches” had time to disappear known as strobing.

iv. Counter Application

Digital Clock.

Automobile Parking Control.

Parallel to Serial Data Conversion (MULTIPLEXING)

Digital Clock

Logic diagram display second, minutes and hours.

60Hz sinusoidal AC voltage connect to 60Hz pulse waveform and divide to 1Hz by using divide-by-60 (include divide-by-10 and divide-by-6).

Both second and minutes produce divide-by-60 counter and it will count from 0 to 59.

This digital clock use synchronous decade counter in implementation.

Simplified logic diagram for a 12-hour digital clock.

Continue in the next class

Logic diagram of typical divide-by-60 counter using 74LS160A synchronous decade counters. Note that the

outputs are in binary order (the right-most bit is the LSB).

Digital Clock = hours definition

Hours counter implement with decade counter and flip-flops.

Initially both decade counter flip-flops = Reset.Decode-12 and decode-9 output = High, so

decade counter through all state from 0 to 9 and recycle from 9 to 0.

Flip-flops goes SET state (J=1, K=0) so it will illuminate (nyala) segment 1 on 10-hours display.

In state12, Q2 output decade counter is High, so flip-flops still SET and decode-12 gates output = LOW.

Logic diagram for hours counter and decoders. Note that on the counter inputs and outputs, the right-

most bit is the LSB.

Automobile Parking Control = Counter Application

Use up/down counter to solve problem.Monitor available space in the one-100 space

parking garage and provide full condition by display sign and lower gate bar at entrance.

The system consist :-- opto-electronic sensor at entrance and exit garage.- up/down counter.

- interface circuit use counter output to turn full-sign on/off and lower/raise gate bar at entrance.

Functional block diagram for parking garage control.

Logic diagram for modulus-100 up/down counter for automobile parking control.

Automobile Parking Control = Definition

up/down use 2-cascade IC. Counter initial preset to 0 by using parallel data input. Each car enter garage break a light beam and activate

sensor. Positive-pulse set SR latches on leading edge. Low on Q’ output latches put counter UP mode. Sensor pulse goes through NOR-Gates and clock the counter

on LOW-to-HIGH transition. When cars enter garage, counter increase by 1. When count last stage (100 unit) the MAX/MIN = High and it

activate light Full-Sign and low gate bar. When car exit, sensor produce (positive pulse) which Reset

SR latches and put counter DOWN mode. So, it will decrease. If garage full and car leave, MAX/MIN = Low, so it will turning

off Full-Sign and raising the bar gate.

Parallel to Serial Data Conversion (MULTIPLEXING). = Counter Application

Parallel data bit on MUX input convert to serial data bit on single transmission line.

Parallel data = a group of bit appear on parallel line in time sequence.

Serial data = a group of bit appear on single line in time sequence.

Counter goes binary sequence from 0 to 7.- each bit start D0.- select and pass through MUX output line.- after 8 clock pulses, data byte has been convert to serial format and sent out transmission lines.

Parallel-to-serial data conversion logic.