Ch01.pptxcomputer organization and architecture schools

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1. Chapter 1 Introduction to Digital Systems

2. Digital computer - a digital system that performs various computational tasks. The word “digital” implies that the information in the computer is repre­sented by variables that take a limited number of discrete values. These values are processed internally by components that can maintain a limited number of discrete states. Digital computers use the binary number system, which has two digits: 0 and 1. A binary digit is called a bit . Information is represented in digital computers in groups of bits . 2 1.1 Digital Computers

3. By using various coding techniques, groups of bits can be made to represent not only binary numbers but also other discrete symbols, such as decimal digits or letters of the alphabet. A computer system is subdivided into two functional entities: hardware and software . 3 Cont….

4. Computer Hardware CPU Memory Program Memory(ROM) Data Memory(RAM) I/O Device Interface : 8251 SIO, 8255 PIO….. Input Device : Keyboard, Mouse, Scanner Output Device : Printer, Plotter, Display Storage Device(I/O): FDD, HDD, 4 Memory CPU IOP Input Device Output Device Cont…. Figure 1-1 Block Diagram of a digital Computer

5. Program(S/W) A sequence of instruction S/W = Program + Data The data that are manipulated by the program constitute the data base Application S/W DB, word processor, Spread Sheet System S/W Consist, collection of software whose purpose is more effective usage of computers. OS, Firmware, Compiler, Device Driver 5 Application S/W Operating System Computer H/W API ROM BIOS Cont….

6. 6 Computer organization Encompasses all physical aspects of computer systems. E.g., control signals, memory types. Become familiar with how various circuits and components fit together to create working computer systems. How does a computer work? Computer Architecture Logical aspects of system implementation as seen by the programmer. Structure and behavior of the computer system. Hardware Components + ISA(Instruction set architecture) Cont….

7. Cont…. “Hardware Components” - CPU(Control, Data path), Memory, I/O devices “ ISA”? - Instructions, Addressing modes, Instruction and data formats How do I design a computer? Why we study computer organization and architecture ? Design better programs, including system software such as compilers, operating systems, and device drivers. Optimize program behavior. Evaluate (benchmark) computer system performance. Understand time, space, and price tradeoffs. 7

8. Example IBM ( International Business Machines Corporation) , SUN and Intel ISAs, it is possible to purchase processors which execute the same instructions from more than one manufacturer All these processors may have quite different internal organizations but they all appear identical to a programmer, because their instruction sets are the same Organization & Architecture enables a family of computer models Same Architecture, but with differences in Organization Different price and performance characteristics. 8 Cont….

9. 9 Computers consist of many things besides chips. Before a computer can do anything worthwhile, it must also use software. Writing complex programs requires a “divide and conquer” approach, where each program module solves a smaller problem. Complex computer systems employ a similar technique through a series of virtual machine layers. 1.2 The Computer Level Hierarchy

10. 10 Each virtual machine layer is an abstraction of the level below it. The machines at each level execute their own particular instructions, calling upon machines at lower levels to perform tasks as required. Computer circuits ultimately carry out the work. Cont….

11. 11 Level 6: The User Level Program execution and user interface level. The level with which we are most familiar. Run like word processors, graphics package programs or games. Level 5: High-Level Language Level The level with which we interact when we write programs in languages such as C, Pascal, Lisp, and Java. Languages translated (with compiler or interpreter) to a language the machine can understand. Cont….

12. 12 Level 4: Assembly Language Level Acts upon assembly language produced from Level 5, as well as instructions programmed directly at this level. Level 3: System Software Level Deals with operating system instructions Controls executing processes on the system. Protects system resources. instructions translated from assembly language to machine language are passed through this level unmodified. Cont….

13. 13 Level 2: Machine Level Also known as the Instruction Set Architecture (ISA) Level. Consists of instructions that are particular to the architecture of the machine. Programs written in machine language need no compilers, interpreters, or assemblers. Level 1: Control Level A control unit makes sure that instructions are decoded and executed properly and that data is moved where and when it should be. Control units can be microprogrammed or hardwired . A microprogram is a program written in a low-level language that is implemented by the hardware. Cont….

14. 14 Hardwired control units consist of hardware that directly executes machine instructions. Machine instructions produced in level-2 are fed into this microprogram, which interprets the instructions by activating hardware suited to execute the original instruction. Level 0: Digital Logic Level This level is where we find digital circuits (the chips). Digital circuits consist of gates and wires. These components implement the mathematical logic of all other levels. Cont….

15. 15 On the ENIAC, all programming was done at the digital logic level. Programming the computer involved moving plugs and wires. A different hardware configuration was needed to solve every unique problem type. Configuring the ENIAC to solve a “simple” problem required many days labor by skilled technicians. 1.3 Von Neumann Model

16. 16 Inventors of the ENIAC, John Mauchley and J.Presper Eckert, conceived of a computer that could store instructions in memory. The invention of this idea has since been ascribed to a mathematician, John von Neumann, who was a contemporary of Mauchley and Eckert. Stored-program computers have become known as von Neumann Architecture systems. Cont….

17. 17 Today’s stored-program computers have the following characteristics: Three hardware systems: A central processing unit (CPU) A main memory system An I/O system The capacity to carry out sequential instruction processing. A single data path between the CPU and main memory. This single path is known as the von Neumann bottleneck . Cont….

18. 18 This is a general depiction of a von Neumann system: These computers employ a fetch-decode-execute cycle to run programs as follows . . . Cont….

19. 19 The control unit fetches the next instruction from memory(RAM) using the program counter to determine where the instruction is located. Control unit accesses instructions in sequence. Cont….

20. 20 The instruction is decoded into a language that the ALU can understand (decoded by the control unit) Cont….

21. 21 Any data operands required to execute the instruction are fetched from memory and placed into registers within the CPU. Cont….

22. 22 The ALU executes the instruction and places results in registers or memory. Finally instructions are stored in the main memory. Cont….

23. 23 Conventional stored-program computers have undergone many incremental improvements over the years. These improvements include adding specialized buses , floating-point units , and cache memories , to name only a few. But enormous improvements in computational power require departure from the classic von Neumann architecture. Adding processors is one approach. 1.4 Non-Von Neumann Model

24. 24 In the late 1960s, high-performance computer systems were equipped with dual processors to increase computational throughput. In the 1970s supercomputer systems were introduced with 32 processors . Supercomputers with 1,000 processors were built in the 1980s. In 1999, IBM announced its Blue Gene system containing over 1 million processors. Cont….

25. 25 Parallel processing is only one method of providing increased computational power. It refers to the ability of computer system to do multiple computational activities simultaneously with out the need for CPU to manage and direct flow of data and instruction More radical systems have reinvented the fundamental concepts of computation. These advanced systems include genetic computers, quantum computers, and dataflow systems. Data can be fetched at the same time. Cont….

26. The manipulation of binary information is done by logic circuit called “gate”. Gates are blocks of hardware that produce signals of binary 1 or 0 when input logic requirements are satisfied. 26 1.5 Logic Gates and Boolean Algebra

27. 27 Cont….

28. In the latter part of the nineteenth century, George Boole incensed philosophers and mathematicians alike when he suggested that logical thought could be represented through mathematical equations. How challenge anyone suggest that human thought could be encapsulated and manipulated like an algebraic formula? Computers, as we know them today, are implementations of Boole’s Laws of Thought . 28 Cont….

29. Boolean Algebra is an algebra for the manipulation of objects that can take only two values. Deals with binary variable (A, B, x, y: T/F or 1/0) + logic operation (AND, OR, NOT…) Boolean Function : described by an algebraic expression consisting of binary variables, the constants 0 and 1, and the logic operation symbols + , . , ’ F(x, y, z) = x + y’z The relationship between a function and its binary variables can be represented in a truth table . 29 Cont…. x y z F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 n Combination Variable n = 3

30. To represent a function in a truth table we need a list of the 2 n combinations of n binary variables. A Boolean function can be transformed from an algebraic expression into a logic diagram composed of AND, OR, and inverter gates. 30 Cont….

31. Purpose of Boolean Algebra To facilitate the analysis and design of digital circuit. Convenient Tools Truth table : relationship between binary variables Logic diagram : input-output relationship Find simpler circuits for the same function Digital computers contain circuits that implement Boolean functions. The simpler that we can make a Boolean function, the smaller the circuit that will result. Simpler circuits are cheaper to build, consume less power, and run faster than complex circuits . 31 Cont….

32. With this in mind, we always want to reduce our Boolean functions to their simplest form. There are a number of Boolean identities that help us to do this. 32 Cont…. Table: Basic Identities of Boolean Algebra

33. 33 We can use Boolean identities to simplify the function: Examples: Cont….

34. F= AB’ + C’D + AB’ + C’D = x + x (let x= AB’ + C’D) = x = AB’ + C’D F= ABC + ABC’ + A’C = AB(C + C’) + A’C = AB + A’C 34 Cont…. Figure : Two logic diagrams for the same Boolean function.

35. Boolean functions can also be expressed in standardized or canonical form. There are two canonical forms for Boolean expressions: sum-of-products and product-of-sums. Recall the Boolean product is the AND operation and the Boolean sum is the OR operation. In the sum-of-products form, ANDed variables are ORed together. For example: In the product-of-sums form, ORed variables are ANDed together: For example: 35 Cont….

36. It is easy to convert a function to sum-of-products form using its truth table. We are interested in the values of the variables that make the function true (=1). Using the truth table, we list the values of the variables that result in a true function value. In each product term, you must then complement any variables that are 0 for that row. Each group of variables is then ORed together. 36 Cont….

37. The sum-of-products for our function is: 37 We note that this function is not in simplest terms. Our aim is only to rewrite our function in canonical sum-of-products form. Cont….

38. DeMorgan’s law – it provides an easy way of finding the complement of a Boolean function. Recall DeMorgan’s law: Replace each variable by its complement and change all ANDs to ORs and all ORs to ANDs. Thus, we find the complement of: 38 Cont….

39. Map Simplification Karnaugh Map(K-map) -is map method for simplifying Boolean expressions.( graphical representation) is a matrix consisting of rows and columns that represent the output values of a Boolean function. The output values placed in each cell are derived from the minterms of a Boolean function. A minterm is a product term that contains all of the function’s variables exactly once, either complemented or not complemented. 39 Cont….

40. For example, the minterms for a function having the inputs x and y are: Consider the Boolean function, Its minterms are: 40 Cont….

41. Similarly, a function having three inputs, has the minterms that are shown in this diagram. 41 Cont….

42. A K-map has a cell for each minterm. This means that it has a cell for each line for the truth table of a function. The truth table for the function F(x,y) = xy is shown at the right along with its corresponding K-map. 42 Cont….

43. As another example, we give the truth table and K-map for the function, F(x,y) = x + y at the right. This function is equivalent to OR of all of the minterms that have a value of 1. Thus: 43 Cont….

44. We reduce our complicated expression to its simplest terms by finding adjacent 1s in the Kmap that can be collected into groups that are powers of two. In our example, we have two such groups. Can you find them? The best way of selecting two groups of 1s from our simple Kmap is shown below. We see that both groups are powers of two and that the groups overlap. 44 Cont….

45. The rules of Kmap simplification are: Groupings can contain only 1s; no 0s. Groups can be formed only in the same row or in the same column (diagonal groups are not allowed). The number of 1s in a group must be a power of 2 even if it contains a single 1. The groups must be made as large as possible. Groups can overlap and wrap around the sides of the Kmap. 45 Cont….

46. A Kmap for three variables is constructed as shown in the diagram below. We have placed each minterm in the cell that will hold its value. Notice that the values for the yz combination at the top of the matrix form a pattern that is not a normal binary sequence. (The input values for the Kmap must be ordered so that each minterm differs in only one variable from each neighbor) 46 Cont….

47. Thus, the first row of the Kmap contains all minterms where x has a value of zero. The first column contains all minterms where y and z both have a value of zero. 47 Cont….

48. Consider the function : Its Kmap is given below. What is the largest group of 1s that is a power of 2? 48 Cont….

49. This grouping tells us that changes in the variables x and y have no influence upon the value of the function: They are irrelevant. This means that the function, reduces to F(x) = z. 49 Cont….

50. Now for a more complicated Kmap. Consider the function: Its Kmap is shown below. There are (only) two groupings of 1s. Can you find them? 50 Cont….

51. In this Kmap, we see an example of a group that wraps around the sides of a Kmap. This group tells us that the values of x and y are not relevant to the term of the function that is encompassed by the group. What does this tell us about this term of the function? 51 What about the green group in the top row? Cont….

52. 52 Recall that we had six minterms in our original function! Cont….

53. Our model can be extended to accommodate the 16 minterms that are produced by a four-input function. This is the format for a 16-minterm Kmap. 53 Cont….

54. We have populated the Kmap shown below with the nonzero minterms from the function: Can you identify (only) three groups in this Kmap? 54 Recall that groups can overlap. Cont….

55. Our three groups consist of: A purple group entirely within the Kmap at the right. A pink group that wraps the top and bottom. A green group that spans the corners. Thus we have three terms in our final function: 55 Cont….

56. Integrated Circuits is a small silicon semiconductor crystal called a chip , containing the electronic components for the digital gates. The various gates are interconnected inside the chip to form the required circuit. IC’s are the tiny electronics circuit used to perform the several operations like Amplifier , timer , counter , oscillator , microcontroller or a computer memory . 56 1.6. Common digital components

57. As the technology of ICs has improved, the number of gates that can be put in a single chip has increased considerably. The differentiation between those chips that have a few internal gates and those having hundreds or thousands of gates is made by a customary reference to a package as being either a small , medium , or large-scale integration device. SSI(Small Scale Integration Device)-contain several independent gates in a single package. The inputs and outputs of the gates are connected directly to the pins in the package. The number of gates is usually less than 10 and is limited by the number of pins available in the . 57 Cont….

58. MSI(Medium-scale integration)- have a complexity of approximately 10 to 200 gates in a single package. They usually perform specific elementary digital functions such as decoders, adders, and registers. LSI (Large-scale integration) - contain between 200 and a few thousand gates in a single package. They include digital systems, such as proces­sors, memory chips, and programmable modules. VLSI(Very Large Scale Integration)- contain thousands of gates within a single package. Examples are large memory arrays and complex microcomputer chips. 58 Cont….

59. Registers is a group of flip-flops with each flip-flop capable of storing one bit of information. They can be implemented using D flip-flops. One D flip-flop is equivalent to a 1-bit register, so a collection of D flip-flops is necessary to store multi-bit values. A 32-bit register requires 32 D flip-flops. These collections of flip-flops must be clocked to work in unison. At each pulse of the clock, input enters the register and cannot be changed (and thus is stored) until the clock pulses again. 59 Cont….

60. Binary Counter It goes through a predetermined sequence of states as the clock pulses.(follows the binary number sequence ) Counters are found in almost all equipment containing digital logic. They are used for counting the number of occurrences of an event and are useful for generating timing signals to control the sequence of operations in digital computers. 60 Cont….

61. Memory Units is a collection of storage cells together with associated circuits needed to transfer information in and out of storage. It stores binary information in groups of bits called words . A memory word is a group of l's and 0's and may represent a number , an instruction code , one or more alphanumeric characters , or any other binary-coded information. 61 Cont….

62. A connected arrangement of logic gates with a set of inputs and outputs. It produces a specified output at the instant when input values are applied. i f i 1 f 1 i n f m 62 1.7. Combinational Circuits Combinational Circuits (Logic Gates) .. . .. .

63. Half-Adder The most basic digital arithmetic circuit is the addition of two binary digits. A combinational circuit that performs the arithmetic addition of two bits is called a half-adder . 63 Design Example

64. Full Adder We can change our half adder into to a full adder by including gates for processing the carry bit. Full adder is a combinational circuits that forms the arithmetic sum of three input bit(Carry considered ). 64 Cont….

65. Decoder a combinational circuit that converts binary information from the n coded inputs to a maximum of 2 n unique outputs. Decoders have a wide variety of applications in digital systems such as data demultiplexing, digital display, digital to analog converting, memory addressing. 65 This is a block diagram for a decoder. Cont….

66. This is what a 2-to-4 decoder looks like on the inside. 66 If x = 0 and y = 1, which output line is enabled? Cont….

67. Multiplexer(data selector ) It selects a single output from several inputs. The particular input chosen for output is determined by the value of the multiplexer’s control lines. The term multiplex means “ many into one . Fig: 4 to 1 Multiplexer 67 Cont….

68. 68 1.8. Sequential Circuits Combinational Circuit Flip-Flops Input Output Clock A sequential circuit is an interconnection of F/F and Gate Sequential circuits are broadly classified into two main categories, known as synchronous or clocked and asynchronous or unclocked sequential circuits, depending on the timing of their signals. synchronous sequential circuit Is a sequential circuit whose behavior can be defined from the knowledge of its signal at discrete instants of time. Combinational Circuit = Gate Sequential Circuit = Gate + F/F

69. In these systems, the memory elements are affected only at discrete instants of time. The synchronization is achieved by a timing device known as a system clock . State changes are controlled by clocks . A “ clock ” is a special circuit that sends electrical pulses through a circuit. Clocks produce electrical waveforms such as the one shown below 69 Cont….

70. Asynchronous sequential circuit Is a sequential in which they become active the moment any input value changes. (The output will be affected whenever the input changes) There is no need to wait for a clock pulse. Asynchronous circuits are faster than synchronous sequential circuits. However, in an asynchronous circuit, events are allowed to occur without any synchronization. And in such a case, the system becomes unstable. Since the designs of asynchronous circuits are more tedious and difficult, their uses are rather limited. 70 Cont….

71. In clocked sequential circuits, the transition from present state to next state is activated by the presence of a clock signal. Circuits can change state on the rising edge, falling edge, or when the clock pulse reaches its highest voltage. Circuits that change state on the rising edge, or falling edge of the clock pulse are called edge-triggered . Level-triggered circuits change state when the clock voltage reaches its highest or lowest level. 71 Cont….

72. To retain their state values, sequential circuits rely on feedback . Feedback in digital circuits occurs when an output is looped back to the input . A simple example of this concept is shown below. If Q is 0 it will always be 0, if it is 1, it will always be1. Why? 72 Cont….

73. Flip-Flop The storage elements employed in clocked sequential circuit which are capable of storing binary information. It can have only two states, either the 1 state or the 0 state. The state of Q is called the state of the flip-flop, whereas the state of Q' is called the complementary state of the flip-flop. 73 Cont….

74. The two outputs are complementary to each other. If Q is 1 i.e. , Set, then Q' is 0; i.e. , Reset, then Q' is 1. That means Q and Q' cannot be at the same state simultaneously. If it happens by any chance, it violates the definition of a flip-flop and hence is called an undefined condition . The most common types of flip-flops are presented below. SR Flip-Flop 74 Cont….

75. The behavior of an SR flip-flop is described by a characteristic table. Q(t) means the value of the output at time t. Q(t+1) is the value of Q after the next clock pulse. We can describe any flip-flop by using a characteristic table , which indicates what the next state should be based on the inputs and the current state 75 Cont….

76. The SR flip-flop actually has three inputs: S, R, and its current output, Q . Thus, we can construct a truth table for this circuit, as shown at the right. Notice the two undefined values. When both S and R are 1, the SR flip-flop is unstable. 76 The SR flip-flop should not be pulsed when S = R = 1 since it produces an indeterminate next state . Cont….

77. JK Flip-Flop The SR flip-flop can be modified to provide a stable state when both inputs are 1. This modified flip-flop is called a JK flip-flop , shown at the right.(“JK” is in honor of Jack Kilby ) Fig: Modified SR flip-flop The characteristic table indicates that the flip-flop is stable for all inputs. 77 Cont….

78. D Flip-Flop the output of the flip-flop remains the same during subsequent clock pulses. The output changes only when the value of D changes. The D flip-flop is the fundamental circuit of computer memory. D flip-flops are usually illustrated using the block diagram shown below. 78 Cont….