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ECE 209 – Logic and computing devices

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1 ECE 209 – Logic and computing devices
Pre-labs for ECE 209 Created: 9/4/12 by Madhabi Manandhar Last Updated: 12/20/2012

2 Laboratory 0 – Lab introduction

3 Outline Syllabus highlights Good lab procedures for ECE 201 Hardware used in lab ECE 209 lab kit NI-ELVIS –II Software used in the lab Digital Works Safety video

4 Syllabus Highlights Grade Composition: Grading Scale: A: 90-100%
25 % Pre-lab preparation and design 25% Class performance and demonstration of functional circuits 30% Full lab reports 20% Final project and presentation Grading Scale: A: % B: 75-89% C: 60-74% D: 50-59% F: <50%

5 Syllabus Highlights (cont.)
Pre-lab Preparation and Design (25% of grade): Thoroughly read the experiment in the manual before coming to the lab. Pre-lab reports are to be turned in before each lab and may consist of simulation(s), diagrams, truth tables, K-maps, etc. Wiring you circuits prior to coming to lab will make the lab quicker and easier for both the student and instructor. Pre-wiring circuits will also reduce the chance of students not having enough time to complete the lab.

6 Syllabus Highlights (cont.)
Class Performance/Functional Circuits (25% of grade): Attend each lab and participate Correctly wire the circuits required in the lab manual and demonstrate that the circuit functions correctly to the instructor Attendance is mandatory for every lab; however, if the instructor is not in the classroom within 15 minutes after the class is scheduled to start, then the students are free to leave (unless they have been told otherwise in advance).

7 Syllabus Highlights (cont.)
Full Lab Reports (30% of grade): Throughout the semester there will be 3 full lab reports assigned, each will count as 10% of your overall grade. These reports must be typed using a word processor. Grades will be based on organization, content, neatness, accuracy, conclusions, and format. A standard format is as follows (format may vary with different instructors): Title Page (Title, date, due date, author, lab partner(s)) Objectives (Succinctly state the purpose of the lab) Procedure (State what you did (circuit diagrams) and present results) Conclusion College of Engineering Honor Code and Signature

8 Syllabus Highlights (cont.)
Final Project and Presentation (20% of grade): There is NOT A FINAL EXAM for this lab course. Instead there will be a project involving design, simulation, and analysis of a digital-circuit related to a concept of your choice. You may work individually or in groups of 2 One report will be required for each group Your group will give a presentation about your project during the last lab session You will receive more information regarding this project in the second half of the semester.

9 Good lab procedures Be very careful while wiring circuits Don’t leave wire dangling about Make sure all the connections are made correctly (reverse power leads can destroy your IC chips) Before wiring always draw a circuit diagram with pin numbers and chips labeled While wiring and rewiring turn off the power Avoid messy wiring Handle equipment carefully Before leaving lab check to make sure your bench position is neat and orderly

10 Hardware – ECE 209 Lab Kit Protoboard: Inserting IC chips on a protoboard

11 Hardware – ECE 209 Lab Kit (cont.)
Integrated Circuits (ICs): IC pin numbers: The position of pin 1 is determined by a dot or notch on the IC. The numbers typically increase in the counterclockwise direction (but there are exceptions). Once we know the pin numbers, we can use the chip pin-out to create our circuit. Notch Actual Chip Chip Pin-out Diagram

12 Hardware – ECE 209 Lab Kit (cont.)
Each IC chip has a number stamped on it, identifying what type of logic chip it is. For example the chip below is a 7486 logic chip which contains 4, 2-input XOR gates. Once we know the IC number, we can find the chip pin-out in pages in the lab manual.

13 Hardware – ECE 209 Lab Kit (cont.)
IC Handling: Before using the ICs we must first straighten out the legs by gently flattening the IC on a table top as shown below. Be careful, the legs/pins are very fragile.

14 Hardware – ECE 209 Lab Kit (cont.)
Removing ICs: Ideally we would use an IC extractor, but we will usually just use a pencil to gently remove ICs from the protoboard. First loosen the IC on one end, and then loosen as shown below. This is to prevent the legs/pins from bending. Loosen One End of the IC Loosen Second End and Remove

15 Examples of Basic Gates – AND gate
An AND gate can be depicted by 2 switches in series Ref:

16 Examples of Basic Gates – OR gate
An OR gate can be depicted by 2 switches in parallel Ref:

17 Hardware – NI ELVIS II 1: On-Off switch 2: PWR SEL Jumper 3: Power Supply 4: Logic Inputs 5: Lamp Monitors (LEDs) 6: Function Generator 7: Analog Inputs

18 Hardware – NI ELVIS II (cont.)
Powering the Circuits: For our circuits to operate the NI-ELVIS board must be turned on (there are two switches which need to be “on”, the one pictured in the previous diagram and one on the back right side of the board). The ICs in our circuits will require Vcc (+5 V) and GND (ground) according to the pin-outs. The pins for Vcc and GND are in the “Power Supply” area of the board; area 3 in the previous slide.

19 Hardware – NI ELVIS II (cont.)
Digital Inputs: Most, if not all of our circuits will require digital inputs. i.e. inputs that are either logic 1 (+5 V) or logic 0 (GND). We could manually move a wire between the +5 V and GND pins, but it is easier to use a specialized pin that we can change between +5 V and GND with software. The specialized pins that we will use as digital inputs to our circuits are shown in area 4 of the NI-ELVIS diagram (DI0 – DI7).

20 Hardware – NI ELVIS II (cont.)
Controlling Digital Inputs: Open the “NI ELVISmx Instrument Launcher” on the computer and the following GUI will appear. Select “DigOut” and the GUI to the right will appear. Hit the “Run” button Click the oval corresponding to the desired input to toggle it between +5 V and GND DI0=oval 0, DI1=oval 1, etc. “Ovals”

21 Software – Digital Works
Simulations using Digital Works: There is a link on the lab homepage (for 32 bit machines) as well as a link in the syllabus (for 64 bit machines) where you can download Digital Works (DW). Using DW we can simulate circuits and determine if they are functioning how they should before actually building a circuit on our protoboard. Labeling chips and pin numbers in the simulation will also make it much easier to wire circuits in the lab. For a basic introduction to using DW go the the “Digital Works Introduction” link on the lab homepage.

22 Software – Digital Works (cont.)
Basic Logic Gates Interactive Input LED (output) Annotation (labeling) Wiring Tool Run button Object Interaction

23 Software – Digital Works (cont.)
The following is an example of simulating a OR gate in Digital Works Z = X + Y

24 Contact Information Instructor: Name: Office: Phone: Office Hours: As needed ( for appointment) Lab Coordinator: Name: Dr. Timothy Burg Office: 307 Fluor Daniel (EIB) Phone: (864)

25 Safety Video

26 Laboratory 1 – Logic gates: A smart lighting system

27 Introduction to Laboratory 1
Objective: Explore notion of combinational circuits and basic combinational design Requirements Digital works simulation for all 3 circuits Verbal description of the function of final circuit Truth table for first function (the light controller)

28 Lab overview Design a circuit that controls a light with 5 input The light is turned on when Burglar Alarm (B) detects an intruder Master Light Switch (M) is on An Auxiliary Switching system (A1, A2) is on and a Person (P) is present in the room (person detector is on)

29 Logic equation : XOR function for auxiliary switching system : : Person detected AND auxiliary switching system on : Master Switch is on OR Person is detected AND Auxiliary switching system is on Desired lighting function is

30 Building a digital light control

31 Implementing a Function with different gates
Implement the XOR function using only AND and OR gates Simulate the circuit in digital works Wiring the circuit is optional.

32 Realizing an Arbitrary Boolean Function
Design a circuit using only truth tables and logic function Logic function is Simulate and wire the circuit using AND, OR and NOT gates

33 Preparations for Next Week
Next week’s lab Encoding/Decoding: The Seven-Segment Display Requirements: Simulation of functional seven-segment display circuit Truth table for all seven segments and all seven functions in MSOP

34 Laboratory 2 – Encoding/Decoding: The Seven-segment display

35 Introduction to Laboratory 2
Objective: Become familiar with the seven-segment LED display, encoding/decoding, and BCD (binary coded decimal) Requirements: Simulation of functional seven-segment display circuit Truth table for all seven segments and all seven functions in MSOP

36 Decoding/Encoding Decoding: Encoding:
Decoding is the conversion of a n-bit input code to a m-bit output code with n ≤ m ≤ 2n. As an example, the inputs (Ai) and the outputs (Di) for a 2-to-4 line decoder are shown below: Encoding: Encoding is the inverse operation of decoding. An encoder converts a m-bit input to a n-bit output with n ≤ m ≤ 2n. The above table would represent an encoder if the D’s were inputs and the A’s were outputs. M. M. Mano and C. R. Kime, Logic and Computer Design Fundamentals

37 Binary Coded Decimal (BCD)
When converting from decimal to BCD we convert each decimal digit individually using the following table: A decimal number in BCD is the same as its equivalent binary number only when the number is between 0 and 9 (inclusive). A BCD number greater than 10 has a representation different from its equivalent binary number. This can be seen below for the conversion of decimal 185: (185)10 = ( )BCD = ( )2 1 8 5 M. M. Mano and C. R. Kime, Logic and Computer Design Fundamentals

38 Seven-Segment Display
Decimal numbers are displayed by a seven-segment display as shown in the figure The truth table and logic function for segment A are

39 Seven-Segment Display (cont.)
There are two types of seven segment displays Common Anode (what we have) Common connection tied to +5v Logic low inputs used to light LED Common Cathode Common connections tied to ground Logic high input lights up LED 220 Ω resisters critical to limit current through LEDs

40 7447 BCD to Seven-Segment Display
A truth table can be made for all of the segments, but because this function is very common, a single chip has been standardized to perform this conversion. The chip is the 7447. The chip can be connected as follows

41 Preparation for next week
Next week’s lab - Combinational Circuits: Parity Generation and Detection Requirements K-map for parity generator and detector Truth table for parity detector Simulation of functional parity generator/detector

42 Laboratory 3 – Combinational Circuits: Parity generation and detection

43 Introduction to Laboratory 3
Objective: Familiarize students with combination circuits Requirements K-map for parity generator and detector Truth table for parity detector Simulation of functional parity generator/detector

44 Combinational Circuit
Circuit implemented using Boolean circuits Uses gates exclusively, so that it deals with boolean functions Cannot store memory – Has no provision to store past inputs and outputs Used for doing boolean algebra in computer circuits

45 Karnaugh Map Becomes difficult to implement larger boolean expressions - More expressions -> More gates -> Complex circuit -> Difficult to connect and implement Expressions can be reduced mathematically, but a tough nut to crack Karnaugh Maps makes expression as simple as possible, as well as its solving process Useful for combinational circuit – reduces the boolean expression substantially

46 Section 1 Parity generators

47 Parity Generator Used to detect whether the number of 1s in the input is even or odd, indicated by a parity bit Used for detecting errors in the received data Two types: Even parity – Parity bit -> high, when 1s -> odd. Makes total number of 1s even in the set Odd Parity – Parity bit -> high, when 1s ->even. Makes total number of 1s odd in the set

48 Parity Generator contd…
By your knowledge so far, along with new information, what do you think is the basic parity generator? And what type? How parity bits are used (Even Parity): 1 PARITY BIT PARITY BIT PARITY BIT

49 Parity generator contd…
For an odd parity generator with three inputs and one output, the truth table is X Y Z P 1

50 Parity generator contd..
K-Map for Odd Parity Generator Y’Z’ Y’Z YZ YZ’ 1 X’ X P = X’Y’Z’ + XY’Z + X’YZ +XYZ’

51 Parity Generator contd…
P = X’Y’Z’ + XY’Z + X’YZ +XYZ’ P = [X’(Y’Z’+YZ)] + [X(Y’Z + YZ’)] P = [X’ AND (Y⊕Z)’] + [X AND (Y⊕Z)] Original Number of 2-input gates (4 x NOT) + (6 x AND) + (4 x OR) = 14 gates Number of 2-input Gates for the highlighted expression (2 x NOT) + (1 x XOR) + (2 x AND) + (1 x OR) = 6 gates

52 Parity Generator contd…
6 Gates sound too much still, isn’t it? Let’s check the highlighted equation again: P = [X’ AND (Y⊕Z)’] + [X AND (Y⊕Z)] Let (Y⊕Z) = W P = [X’ AND W’] + [X AND W] P = X’W’ + XW What does this remind you of? P = X XNOR W => P = (X ⊕ W)’ Replacing the value of W P = (X ⊕ Y ⊕ Z)’ Number of 2-input gates now => (2 x XOR) + (1 x NOT) => 3 gates!

53 Section 2 Parity Detectors

54 Parity detector No use of parity generators, if there’s nothing to acknowledge – or check for – the parity bits Chances exist of noise in data sent over a communication channel Errors detected using parity detectors Parity generator and detector go hand-in-hand

55 Parity detector contd…
Odd parity detector for 3 inputs

56 Parity detector contd…
K-Map for Odd parity detector Z’P’ Z’P ZP ZP’ X’Y’ X’Y XY XY’

57 Parity detector contd…
E = (X ⊕ Y ⊕ Z ⊕ P )’ Number of 2-input Gates for the highlighted expression (3 x XOR) + (1 x NOT) = 4 gates

58 Parity generator and detector
Create parity generator and detector circuits and connect them as shown in the figure below Also simulate a communication where a single bit error is introduced to any of the four inputs to parity detector

59 Lab Report Due Next Lab Objective – Goal of the lab Split the report into two parts here Just mention the parts, and start from the same page. No need for separate pages to indicate separate parts.

60 Lab Report contd… Part 1: Parity Generator Schematic Diagram – One will suffice Explanation What is a Parity Generator? Truth Table K-Map Derive the equation that you used in the lab Importance Result – Explain your result as you understood

61 Lab Report contd… Part 2: Parity Detector Schematic Diagram – One will suffice. You can show “P” as an input. No need to attach parity generator circuit to it. Explanation What is a Parity Detector? Truth Table K-Map Derive the equation that you used in the lab Importance Result – Explain your result as you understood

62 Lab Report contd… Conclusions – Write the conclusion based on your experience while working with K-maps, gates, and parity-generator and –detector. Honor Code – Limit to one important paragraph

63 Preparation for next week
Read about binary arithmetic and properties Learn more about K-maps, and how they are used to reduced the number of elements in the expression Understand binary half-adders and full-adders, and difference between them Generate truth tables for half- and full-adders Though half-adder is not mentioned in the lab-manual, we’ll be doing it the next class

64 Laboratory 4 – Binary arithmetic - adders

65 Introduction to Laboratory 4
Objective: Demonstrate knowledge of simple binary arithmetic and mechanics of its use Requirements Simulation of functional Full Adder

66 Half Adder When 2 single bits A and B are added the truth table and K-maps for this operation are as follows: Sum (S) Carry (C) B B 1 A 1 A From the truth table and or K-maps we can determine that the functions for C and S are as shown below.

67 Half Adder (cont.) Now consider the addition of two 8-bit binary numbers: We can see that we are actually adding three bits, two bits from the numbers being added and one additional carry bit. Since the half adder does not take this carry bit (Cin) into consideration a new model is needed. This new model is a full adder.

68 Full Adder The truth table and K-maps for the full adder are shown below. Sum (S) Carry Out (Cout) AB AB Cin 00 01 11 10 1 Cin 00 01 11 10 1 The familiar checkerboard pattern in S and the circled groups in Cout lead to the full adder functions that are shown below.

69 Full Adder (cont.) A circuit diagram which creates the sum (S) and carry (Cout) bits of a full adder is shown below.

70 Building 2-bit Full Adder
Two full adders can be combined to make a 2-bit adder as shown in the diagram below Build a 2-bit adder on your bread-board and test the circuit

71 Preparation for next week
Next week’s lab: MSI Circuits – Four-Bit Adder/Subtractor with Decimal Output Requirements Simulation of functional circuit

72 Laboratory 5 – MSI Circuits – Four-bit adder/subtractor with decimal output

73 Introduction to Laboratory 5
Objective: Familiarize students with MSI technology, specifically adders and also 1’s complement arithmetic Requirements Simulation of functional Full Adder

74 Representation of Negative Numbers as Binary
Ideally, a binary number is represented in an “exponential of 2” number of bits, i.e. 2, 4, 8, 16 … Three types of negative-number representation. Interested only in 1’s complement, i.e. complementing of every bit of the original number to get negative counterpart E.g. 4- bit 1’s Complement 8-bit 1’s complement 7 – -7 – – Why is it known as 1’s complement? Because it is obtained by subtracting the unsigned number from 0’s complement. Try it yourself.

75 4-Bit Adder & Subtractor
The 7483 chip is a 4 bit full adder Subtraction is addition of a positive and a negative number Apart from addition, the chip can be used for 1’s complement subtraction

76 Example of 1’s complement subtraction
Take 1’s complement of 1 i.e. (-1) Add (-1) to 7 Add the carry bit to the result Result of addition is the final result Ref: Wikipedia

77 Building 1’s Complement Subtractor
Take 1’s complement using XOR gates to complement a bit when input is 1 Why not NOT gate? Input to determine the nature of adder 0: Addition 1:Subtraction

78 Steps for 1’s compliment subtraction
If the numbers are in decimal-form, convert them to binary Take 1’s complement of the subrahend. Add the 1’s complement to minuend Instead of keeping carry bit as the extended form of difference, add it to the answer S4 S3 S2 S1 is the final answer for add/subtract


80 Part II use 7-segment display
Display the result in 7-segment display Use the 7447 chip Note : Main circuit does not contain the 4 XOR gates just before the 7447 chip


82 Lab Report – Due Next Lab
Objective – Goal of the lab Equipment used Split the report into two parts here Just mention the parts, and start from the same page. No need for separate pages to indicate separate parts.

83 Lab Report (cont.) Part 1: 1-bit Full Adder Schematic Diagram – DigitalWorks Explanation What is a Full Adder? Truth Table K-Map Mention the equation that you used in the lab

84 Lab Report (cont.) Part 2: 4-bit Subtractor
Schematic Diagram - DigitalWorks Explanation Concept of 1’s complement subtraction A short statement on MSI chip and the one used here Explanation for circuit used, including the usage of gates, resistors, BCD-to-decimal converter, and LED display Truth table for LED display and BCD-to-decimal converter

85 Lab Report (cont.) Result – Answer the questions mentioned in the lab manual Conclusions – Write the conclusion based on your experience while working with K-maps, gates, and parity-generator and –detector. Honor Code – Limit to one important paragraph

86 Preparation for next week
Next week’s lab : Multiplexers and Serial Communication Requirements Simulation of functional circuit

87 Laboratory 6 – Multiplexers and serial communication

88 Introduction to Laboratory 6
Objective: Familiarize students with internal realization of multiplexers and show an application of multiplexers and demultiplexers in serial communications Requirements Simulation of functional circuit

89 Multiplexer A multiplexer is a combinational circuit that selects binary information from 2n input lines and directs the information to a single output line by using n select lines The lab manual gives the analogy of a rotary switch like in the above figure. This is an accurate comparison but note that there is not an actual switch in the multiplexers. The input line that is connected to the output line is determined by the select lines (S0 and S1) and logic gates.

90 Multiplexer (cont.) 0 0 D0 D1 1 0 D2 0 1 D3 1 1

91 Why do we need multiplexers?
Multiplexer (cont.) Why do we need multiplexers? Less Power Consumption in Displays The lab manual gives the example of multiplexing the seven-segment displays of a calculator to reduce power usage and therefore increase battery life What about LED advertisement boards being viewed in slow motion? Communication Systems When there are several independent inputs which need to travel over the same line. Consider the arrangement of phone lines.

92 Demultiplexer A demultiplexer is another type of combinational circuit. The function of a demultiplexer is opposite to the function of a multiplexer. The demultiplexer takes a single input line and sends it to one of 2n output lines depending on the value of the n select lines.

93 Demultiplexer (cont.) Since we do not have a 1-to-8 demultiplexer, we will have to create one from the chip. The contains two 1-to-4 demultiplexers. To do this, make the following connections: Connect “Strobe GA” and “Strobe GB” together  Input line Connect “Data CA” and “Data CB” together  3rd select line Note: The notation for the figures in the lab manual does not match exactly with the pinouts for the chips!

94 Application of multiplexer/demultiplexer
Connect the following circuit to multiplex the segments of the seven-segment display with a serial communication line. Connect “clock” of the to the function generator of the NI ELVIS board. Use a square waveform with a Vpp of 3 volts.

95 Preparation for next week
Next week’s lab : Four – Bit Combinational Multiplier Requirements Simulation of functional circuit

96 Laboratory 7 – Four-bit combinational multiplier

97 Introduction to Laboratory 7
Objective: Practice the combinational design process through the design of a 4-bit multiplier Requirements Simulation of functional circuit No wiring necessary for this lab

98 4 bit multiplication Example of a 4 bit multiplication The individual multiplication can be obtained by the AND operation and 4-bit adder can be used for addition

99 Complete multiplication
Sij represents the jth output of the ith adder S05 , S16 and S7 are carry from the 4 bit adder Only 4 bit adders are needed for addition as P00, S01 and S12 are directly given to the output

100 Preparation for next week
Next week’s lab : Logic Design for a Direct-Mapped Cache Requirements Simulation of functional circuit along with all the macros used

101 Laboratory 8 – Logic design for a direct-mapped cache

102 Introduction to Laboratory 8
Objective: Understand the function and design of a direct-mapped cache Requirements Simulation of functional circuit along with all the macros used No wiring necessary for this lab

103 Terminology 1 Byte = 8 bits (i.e. 1001 0110 is one byte)
1 kilobyte (kB) = 210 bytes = 1,024 bytes (as opposed to the equality: 1 kilometer = 103 meters = 1,000 meters) 1 megabyte (MB) = 220 bytes = 1,048,576 bytes (as opposed to the equality: 1 megameter = 106 meters = 1,000,000 meters) 1 gigabyte (GB) = 230 bytes = 1,073,741,824 bytes (as opposed to the equality: 1 gigameter = 109 meters = 1,000,000,000 meters)

104 Basic Computer Organization
Background The CPU requires data from memory (instructions for programs and numerical data) When a computer needs to read from memory it generates a memory address The next step is to locate where the data associated with the address is currently residing The first memory it checks is the cache, if it is there it is a cache hit, otherwise it is a miss Basic Computer Organization A. S. Tanenbaum, Structured Computer Organization

105 Moving Down the Pyramid
Background (cont.) few ns (10-9 s)/~100 bytes few ns (10-9 s)/few megabytes tens of ns (10-9 s)/thousands of megabytes tens of ms (10-3 s)/few gigabytes several seconds/limited only by budget (kept separate) Moving Down the Pyramid Longer access times (slower) Increased storage capacity (larger) Cost per bit decreases (cheaper) Data most frequently needed is kept in small, fast, but expensive memory. Less frequently needed data is kept in large, slow, and cheap memory. A. S. Tanenbaum, Structured Computer Organization

106 Direct-mapped cache The goal of this lab will be to develop logic which determines whether or not the required data is in the cache (the output will indicate whether we have a cache hit or a miss). Our fictional computer is characterized by the following: 16 bit address bus  216 = 210*26 = 1 kB*64 = 64 kB (total memory) 16 line cache with 256 bytes each  256 B*16 = 28*24 = 210*22 = 1 kB*4 = 4 kB (data from memory that can be stored in the cache) Line2,byte1 Line2,byte2 Line2,byte3 Line2,byte4 Line2,byte256 Line3,byte1 Line3,byte2 Line3,byte3 Line3,byte4 Line3,byte256 Line4,byte1 Line4,byte2 Line4,byte3 Line4,byte4 Line4,byte256 Line1,byte1 Line1,byte2 Line1,byte3 Line1,byte4 Line1,byte256 ... Line16,byte1 Line16,byte2 Line16,byte3 Line16,byte4 Line16,byte256 . Cache Structure

107 Direct-mapped cache (cont.)
The 16 bit memory address is arranged as shown Cache line address indicates which line in the cache the address will be in Tag tells us which block is present (Offset)

108 Example Only memory addresses whose cache line address field matches can be in a particular cache (only one block per cache line). One block

109 Lab Procedure We will not be concerned with the “offset” bits.
We will be working with the “tag” bits of the address which are stored in a tag memory that is associated with the cache. We will also be working with a “valid” bit in the tag memory which indicates if the information in the cache is valid.

110 Lab Procedure (cont.) Based on the information in the previous slides, we will need a 16x5 tag memory. We will implement the tag memory in Digital Works using ROM (initialized according to the table to the right). Inputs to the ROM will be the “cache line address bits” and the “tag” bits of the memory address (i.e. you will need 8 inputs in your simulation). The “cache line address” bits will determine which line in the cache to retrieve the tag from. The retrieved tag bits will then be compared with the tag bits in the memory address. Use a comparator to turn on an LED if the retrieved tag bits are the same as the tag bits in the memory address and the valid bit is a one.

111 The XNOR function can be used to compare 2 bits
Note on comparators The XNOR function can be used to compare 2 bits Two 4-bit binary numbers are the same if and only if the two 1st bits are equivalent and the two 2nd bits are equivalent and the two 3rd bits are equivalent and the two 4th bits are equivalent

112 Preparation for next week
Next week’s lab : Understand the design and restrictions of Sequential Circuits Requirements Simulation of functional circuit

113 Laboratory 9 – Sequential design – three bit counter

114 Introduction to Laboratory 9
Objective: Understand the design and restrictions of Sequential Circuits Requirements Electronic copy of your design. Schematic of final design. State Transition Tables. Karnaugh Maps with Boolean reductions for each variable.

115 Sequential Circuit Some circuits need the knowledge of present – as well as past – inputs, along with the outputs it had generated last time. Combinational circuit can’t be used, as it uses only present inputs, and thus has no memory Sequential circuit comes in handy in such situations The output state of a "sequential logic circuit" depends on: Present Input; Past input; and Past output In general, combinational circuit is a type of sequential circuit Applications: Timers, counters, memory-management, etc. Vital for building larger and more complex electronic circuits, such as robots, computers, and digital watches.

116 Flip-flops Flip-flop is the basic form of a sequential circuit It uses outputs derived from previous inputs to determine the output from the current inputs Types of flip-flops: J-K Flipflop S-R Flipflop D Flipflop T Flipflop

117 Three-bit counter Counter – Basic form of sequential circuit Starts counting from 0-higher number – or higher-number-0 – once signal is given to the circuit Requires 4 flipflops to get 3-bit counting (will use D flipflop for this lab) Inputs: c (c = 0 =>up-count; c=1 =>down-count) Inputs from previous operations: Q1, Q2, Q3 Outputs: Q1, Q2, and Q3

118 c=0 means count up, c=1 means count down D1 can be easily implemented
Logic equations for 3 inputs to D flip flop c=0 means count up, c=1 means count down D1 can be easily implemented D2 can be realized using just 2 XOR gates Factor out c and c’ to obtain a simple form

119 Implementing D3 using JK flip flop
Simplifying D3 Comparing equation of D3 with the logic equation of a JK flip flop gives the input to the JK flip flop


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