Roger L. Tokheim. Chapter 8 Counters Glencoe/McGraw-Hill

Size: px

Start display at page:

Download "Roger L. Tokheim. Chapter 8 Counters Glencoe/McGraw-Hill"

Reginald Booker
5 years ago
Views:

1 Digital Electronics Principles & Applications Sixth Edition Roger L. Tokheim Chapter 8 Counters 2003 Glencoe/McGraw-Hill

2 INTRODUCTION Overview of Counters Characteristics of Counters Ripple Up Counter Ripple Counter with Waveforms Ripple Down Counter Self-stopping Counter Frequency Division using Counters Using Counter ICs Magnitude Comparators Troubleshooting Hints

3 Overview of Counters Counter-by definition One input (clock) Outputs follow defined sequence Common tasks of counter Count up or down Increment or decrement count Sequence events Divide frequency Address memory As memory

4 QUIZ 1. A digital counter has a single clock input with many outputs and the counter follows defined sequence such as 000, 001, 010, 011, 100, 101, 110, 111, 000, etc. (True or False) 2. Several common tasks of a counter are to count up or down, divide frequency, or as memory. (True or False) True True

5 Characteristics of Counters Number of bits (4-bit, 8-bit, etc.) Maximum count 4 bit = 2 4 = 0000 to 1111 in binary 8 bit = 2 8 = to 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

6 QUIZ 1. A4 4-bit counter will count from binary 0000 to The modulus of a counter is the number of state it will cycle through such as a decade counter has a modulus of. 3. Counters can be designed to count up or downward or devised to be self-stopping. (True or False) 10 True 4. A 4-bit counter would have modulus of 4 (mod-4 counter) because it is constructed using four flip-flops. (True or False) False

7 Ripple Counter Clock Input Binary Output Pulse This PS On and the 4-bit CLR next counter input clock has pulse All 16 J-K (8) states flip-flops all FFs and will will count toggle are from because binary each 0000 will through in the receive 1111 a H-to-L and INACTIVE then pulse- reset one back TOGGLE after to another MODE Watch The the counter has ripple a modulus thru the of counter. 16.

8 Ripple Counter With Waveforms Clock Input Binary Output Pulse Clock input FFs triggered on 1s output H-to-L pulse. CLK toggles 1s FF. 1s FF toggles 2s FF. 2s output 2s FF toggles 4s FF. 4s output

12 QUIZ Q#1- Q#2-1 the of the Q#3-2 the of the Q#4- After will will be pulse 8 the output of the mod-16 be 15. the output of the mod-16 will be. counter will be binary Input Pulse Pulses

13 Decade Counter Clock Input Binary Output Pulse Short negative pulse To clear input of each FF All J & K inputs = 1 All PR inputs = 1 To change mod-16 counter to decade counter: Count is at Reset count to 0000 after 1001 (9) count. Next clock pulse will increment counter for a When count hits 1010 reset to short time to 1010 which will activate the NAND gate See added 2-input NAND gate that clears all and reset the counter to JK FFs to 0 when count hits 1010.

19 QUIZ Q#1- Q#2- Q#3- This This The is circuit a gate can (mod-10, generates be described mod-16) a very as up short a counter. LOW (decade, pulse 4-bit) Q#4- After 0110, the counting sequence would be 0111, when 1000, the up count counter. 1001, reaches 1010, 1011, , and 1101, resets 1110, to counter 1111, 0000, to etc. (T or F) ANS: mod-10 decade ANS: ANS: NAND False Input pulses To clear input of each FF

20 Down Counter Pulse Changes from Ripple Up Counter are wiring from Q outputs (instead of Q outputs) to the CLK input of the next FF.

21 QUIZ Q#1- This i can be described as a 3-bit ripple (down-counter, Q#2- Q#3- This The circuit counting up-counter). is a sequence self-stopping of this 3-bit circuit ripple is 111, down 110, counter. 101, (T 100, or 011, F) 010, 001, 000, 111, 110, 101, 100, etc. (T or F) ANS: down-counter ANS: False ANS: True Input pulses

22 Self-Stopping Down Counter The count remained at binary 000. Pulse 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.

24 QUIZ Q#1- This circuit could be described as a 3-bit (decade, Q#2- Q#3-With The self-stopping) 3-input the count OR gate 111, ripple generates the OR gate counter. a outputs (HIGH, a LOW) HIGH when which the places count the decreases left FF in to the 000 toggle which mode. stops the (T or count F) at 000. ANS: self-stopping ANS: LOW ANS: True Input tpulses

25 Counter Used for Frequency Division Hz Hz 400 Hz 50 Hz 2 16 Clock Input 800 Hz

29 QUIZ Q#1- Q#2- is the Q#3- is is the the from from the 1s J-K with an from Q#4- Q#5- the the What The 2s J-K 8s 4s J-K is output the output from with with frequency the an 4-bit an from the 8s J-K of flip-flop 3200 Hz? p with an input counter frequency is referred of of of to as Hz? Hz? Hz? the ANS: 1600 ANS: 800 (divide-by-4, divide-by-16) output. 400 ANS: divide-by Clock Input Frequency? 3200 Hz

30 Using the 7493 Counter IC Counters are available in IC form. Either ripple (7493 IC) or synchronous (74192 IC) counters are available. 100? Hz Hz 400? Hz Hz 800? Hz Hz 1600 Hz 7493 Counter IC wired as a 4-bit binary counter

31 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). A(0) Input binary Input binary A(1) A(2) A(3) B(0) B(1) B(2) 74HC85 Magnitude Comparator A > B A = B A < B HIGH HIGH HIGH B(3)

32 QUIZ Q#1- The 74HC85 Comparator IC compares two 4-bit (binary, Q#2- Q#3- decimal) numbers of the (A and B) and IC generates will be one Q#4- Which output of of the the comparator IC IC will will be be activated of three outputs with with including two two 4-bit 4-bit (1) A = B, (2) A > B, or as as with these two 4-bit binary numbers as (3) inputs? A < B A(0) A(1) A(2) A(3) B(0) B(1) 1010 B(2) B(3) HC85 Magnitude Comparator A>B A = B A < B??? ANS: binary = < ANS: A > B

62 Simple Troubleshooting Hints Feel topofictodetermineifitishot of if it is 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

63 QUIZ 1. The first three steps in troubleshooting are the use of your senses to (1) feel the top of the ICs for overheating, (2) to for broken connections, and (3) to smell for signs of overheating. 2. The forth step in troubleshooting is to use a simple handheld instrument called a to check the power sources at each IC. 3. Your knowledge of the normal operation of the circuit and equipment is very important in troubleshooting. (True or False) look logic probe True

64 REVIEW Overview of Counters Characteristics of Counters Ripple Up Counter Ripple Counter with Waveforms Ripple Down Counter Self-stopping Counter Frequency Division using Counters Using Counter ICs Magnitude Comparators Troubleshooting Hints

CHW 261: Logic Design

CHW 261: Logic Design CHW 26: Logic Design Instructors: Prof. Hala Zayed Dr. Ahmed Shalaby http://www.bu.edu.eg/staff/halazayed4 http://bu.edu.eg/staff/ahmedshalaby4# Slide Digital Fundamentals CHAPTER 8 Counters Slide 2 Counting