Logicgates
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The document provides an overview of logic gates and Boolean algebra. It begins with a review of Boolean algebra concepts like variables being 1 or 0, NOT, OR, and AND operations. It then introduces basic logic gates like NOT, AND, OR, NAND, NOR, and XOR gates. It explains how to determine the output of logic circuits and write Boolean expressions as logic circuits. The document also covers converting between binary and decimal numbers, adding binary numbers using half adders and full adders, and briefly discusses flip-flops and memory.
Logicgates
- 2. Review of Boolean algebra Just like Boolean logic Variables can only be 1 or 0 Instead of true / false 2
- 3. Review of Boolean algebra Not is a horizontal bar above the number _ 0=1 _ 1=0 Or is a plus 0+0 = 0 0+1 = 1 1+0 = 1 1+1 = 1 And is multiplication 0*0 = 0 0*1 = 0 1*0 = 0 1*1 = 1 3
- 4. Review of Boolean algebra ___ Example: translate (x+y+z)(xyz) to a Boolean logic expression (x y z) ( x y z) We can define a Boolean function: F(x,y) = (x y) ( x y) And then write a “truth table” for it: x y F(x,y) 1 1 0 1 0 0 0 1 0 0 0 0 4
- 5. Quick survey I understand the basics of Boolean algebra a) Absolutely! b) More or less c) Not really d) Boolean what? 5
- 6. Basic logic gates Not x x x xy x xyz And y y z x x y x x+y+z Or y y z x xy Nand y x x y Nor y x x y Xor y 6
- 7. Find the output of the following circuit x x+y y (x+y)y y y __ Answer: (x+y)y Or (x y) y 7
- 8. Find the output of the following circuit x x xy xy y y ___ __ Answer: xy Or ( x y) ≡ x y 8
- 9. Quick survey I understand how to figure out what a logic gate does a) Absolutely! b) More or less c) Not really d) Not at all 9
- 10. Write the circuits for the following Boolean algebraic expressions __ a) x+y x x+y x y 10
- 11. Write the circuits for the following Boolean algebraic expressions _______ b) (x+y)x x x+y x+y (x+y)x y 11
- 12. Writing xor using and/or/not p q (p q) ¬(p q) x y x y ____ 1 1 0 x y (x + y)(xy) 1 0 1 0 1 1 0 0 0 x x+y (x+y)(xy) y xy xy 12
- 13. Quick survey I understand how to write a logic circuit for simple Boolean formula a) Absolutely! b) More or less c) Not really d) Not at all 13
- 14. Converting decimal numbers to binary 53 = 32 + 16 + 4 + 1 = 25 + 24 + 22 + 20 = 1*25 + 1*24 + 0*23 + 1*22 + 0*21 + 1*20 = 110101 in binary = 00110101 as a full byte in binary 211= 128 + 64 + 16 + 2 + 1 = 27 + 26 + 24 + 21 + 20 = 1*27 + 1*26 + 0*25 + 1*24 + 0*23 + 0*22 + 1*21 + 1*20 = 11010011 in binary 14
- 15. Converting binary numbers to decimal What is 10011010 in decimal? 10011010 = 1*27 + 0*26 + 0*25 + 1*24 + 1*23 + 0*22 + 1*21 + 0*20 = 27 + 24 + 23 + 21 = 128 + 16 + 8 + 2 = 154 What is 00101001 in decimal? 00101001 = 0*27 + 0*26 + 1*25 + 0*24 + 1*23 + 0*22 + 0*21 + 1*20 = 25 + 23 + 20 = 32 + 8 + 1 = 41 15
- 16. A bit of binary humor Available for $15 at http://www.thinkgeek.com/ tshirts/frustrations/5aa9/ 16
- 17. Quick survey I understand the basics of converting numbers between decimal and binary a) Absolutely! b) More or less c) Not really d) Not at all 17
- 18. How to add binary numbers Consider adding two 1-bit binary numbers x and y 0+0 = 0 0+1 = 1 x y Carry Sum 1+0 = 1 1+1 = 10 0 0 0 0 0 1 0 1 1 0 0 1 1 1 1 0 Carry is x AND y Sum is x XOR y The circuit to compute this is called a half-adder 18
- 19. The half-adder Sum = x XOR y Carry = x AND y x x y y Sum Sum Carry Carry 19
- 20. Using half adders We can then use a half-adder to compute the sum of two Boolean numbers 1 0 0 1 1 0 0 +1 1 1 0 ? 0 1 0 20
- 21. Quick survey I understand half adders a) Absolutely! b) More or less c) Not really d) Not at all 21
- 22. How to fix this We need to create an adder that can take a carry bit as an additional input x y c carry sum Inputs: x, y, carry in Outputs: sum, carry out 1 1 1 1 1 This is called a full adder 1 1 0 1 0 Will add x and y with a half-adder 1 0 1 1 0 Will add the sum of that to the 1 0 0 0 1 carry in 0 1 1 1 0 What about the carry out? 0 1 0 0 1 It’s 1 if either (or both): 0 0 1 0 1 x+y = 10 0 0 0 0 0 x+y = 01 and carry in = 1 22
- 23. The full adder The “HA” boxes are half-adders c X HA S S s Y C C x X HA S c y Y C 23
- 24. The full adder The full circuitry of the full adder c s x y c 24
- 25. Adding bigger binary numbers Just chain full adders together x0 X HA S s0 y0 Y C x1 C X FA S s1 y1 Y C x2 C X FA S s2 y2 Y C x3 C X FA S s3 y3 Y C c 25
- 26. Adding bigger binary numbers A half adder has 4 logic gates A full adder has two half adders plus a OR gate Total of 9 logic gates To add n bit binary numbers, you need 1 HA and n-1 FAs To add 32 bit binary numbers, you need 1 HA and 31 FAs Total of 4+9*31 = 283 logic gates To add 64 bit binary numbers, you need 1 HA and 63 FAs Total of 4+9*63 = 571 logic gates 26
- 27. Quick survey I understand (more or less) about adding binary numbers using logic gates a) Absolutely! b) More or less c) Not really d) Not at all 27
- 28. More about logic gates To implement a logic gate in hardware, you use a transistor Transistors are all enclosed in an “IC”, or integrated circuit The current Intel Pentium IV processors have 55 million transistors! 28
- 29. Pentium math error 1 Intel’s Pentiums (60Mhz – 100 Mhz) had a floating point error Graph of z = y/x Intel reluctantly agreed to replace them in 1994 Graph from http://kuhttp.cc.ukans.edu/cwis/units/IPPBR/pentium_fdiv/pentgrph.html 29
- 30. Pentium math error 2 Top 10 reasons to buy a Pentium: 10 Your old PC is too accurate 8.9999163362 Provides a good alibi when the IRS calls 7.9999414610 Attracted by Intel's new "You don't need to know what's inside" campaign 6.9999831538 It redefines computing--and mathematics! 5.9999835137 You've always wondered what it would be like to be a plaintiff 4.9999999021 Current paperweight not big enough 3.9998245917 Takes concept of "floating point" to a new level 2.9991523619 You always round off to the nearest hundred anyway 1.9999103517 Got a great deal from the Jet Propulsion Laboratory 0.9999999998 It'll probably work!! 30
- 31. Flip-flops Consider the following circuit: What does it do? 31
- 32. Memory A flip-flop holds a single bit of memory The bit “flip-flops” between the two NAND gates In reality, flip-flops are a bit more complicated Have 5 (or so) logic gates (transistors) per flip- flop Consider a 1 Gb memory chip 1 Gb = 8,589,934,592 bits of memory That’s about 43 million transistors! In reality, those transistors are split into 9 ICs of about 5 million transistors each 32
- 33. Quick survey I felt I understood the material in this slide set… a) Very well b) With some review, I’ll be good c) Not really d) Not at all 33
- 34. Quick survey The pace of the lecture for this slide set was… a) Fast b) About right c) A little slow d) Too slow 34