EE 1001 Digital Topics

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EE 1001 Digital Topics

• Introduction to
• Electrical Engineering
• Dr. Chris Carroll
• MWAH 252
• 726-7530
• ccarroll

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Digital Logic Circuits

• Foundation for digital computer design
• Basics are easy. . .
• Discrete, two-valued variables
• Finite number of possible functions
• Complex operations built from easy basics
• Combinational circuits (no memory)
• Sequential circuits (memory)

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Combinational Circuits
AND gate Inputs Output 0 0 0 0 1 0 1 0
0 1 1 1
OR gate Inputs Output 0 0 0 0 1 1 1 0
1 1 1 1
XOR gate Inputs Output 0 0 0 0 1 1 1 0
1 1 1 0
NOT gate Input Output 0 1 1 0
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Sequential Circuits

• Memory stores state of the circuit
• Implemented with flip-flops
• Clock signal switches 0?1?0?1?
• Flip-flop captures data on clock 0?1 change
• D flip-flop is one of several kinds available

D Q clock
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Counters

• Simplest kind of sequential circuit
• Count advances once per clock 0?1
• Count sequence determined by circuit
• Sequence advances unconditionally every time the
  clock goes 0?1
• Flip-flops store the state of the circuit

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Binary UP-counter
Now Next QLQR QLQR 0 0 0 1 0
1 1 0 1 0 1 1 1 1 0 0
D QL clock
D QR clock
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Binary DOWN-counter
Now Next QLQR QLQR 0 0 1 1 1
1 1 0 1 0 0 1 0 1 0 0
D QL clock
D QR clock
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Gray-Code Counter
Now Next QLQR QLQR 0 0 0 1 0
1 1 1 1 1 1 0 1 0 0 0
D QL clock
D QR clock
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3-State, Self-Starting
Now Next QLQR QLQR 0 0 0 1 0 1
1 0 1 0 0 0 1 1 1 0
D QL clock
D QR clock
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Computer Architecture

• How to build a computer
• Many philosophies
• Complex Instruction Set Computer (CISC)
• Reduced Instruction Set Computer (RISC)
• Always three parts of any computer
• Central Processing Unit (CPU)
• Memory (for both program and data)
• Input/Output (I/O)

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Microprocessors

• CPU portion of a computer on a chip
• Requires external memory and I/O
• Examples
• 4004 (first microprocessor, 4-bit)
• 8080 (popular 8-bit)
• 8086 (16-bit, early PCs used this)
• Pentium (32-bit, 64-bit)
• Others

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Microcontrollers

• Entire computer on a chip
• Central Processing Unit (CPU)
• Memory
• Input/Output (I/O)
• Easy to embed in larger systems
• Modern cars include 10s of these

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Hexadecimal (base sixteen!)

• Uses sixteen digits, 0-9 and a-f
• a10, b11, c12, d13, e14, f15
• XY16 X 16 Y
• Or, in binary
• 00002 0 01002 4 10002 8 11002 c
• 00012 1 01012 5 10012 9 11012 d
• 00102 2 01102 6 10102 a 11102 e
• 00112 3 01112 7 10112 b 11112 f

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Advantage of hexadecimal?

• Easy conversion binary ? hexadecimal
• Each 4-bits of binary is 1 hex digit
• 100101102 9616
• 110100102 d216
• 8a16 100010102
• c316 110000112

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Summary

• Digital is everywhere!
• Even analog things can be digitized
• Complexity is manageable
• High performance, low cost