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Building a Computer from Scratch: A Hardware Lab Sequence for Computer Science Students

Building a Computer from Scratch: A Hardware Lab Sequence for Computer Science Students. Michael Black American University mblack@american.edu CCSC East ~ October 10, 2008. Presentation Overview. The Problem with Computer Organization Objectives Challenges Lab Sequence Student Response

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Building a Computer from Scratch: A Hardware Lab Sequence for Computer Science Students

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  1. Building a Computer from Scratch: A Hardware Lab Sequence for Computer Science Students • Michael Black • American University • mblack@american.edu • CCSC East ~ October 10, 2008

  2. Presentation Overview • The Problem with Computer Organization • Objectives • Challenges • Lab Sequence • Student Response • Future Work

  3. Computer Organization • A dense course: • microprocessor, cache, assembly language, instruction set design, datapath/control, some digital design • 4-credit course • 50-minute laboratory period / week

  4. Student Profile • No prior electronic experience • Sophomore and junior students • Have had one introductory programming course • 8 to 16 students • CS Majors, CS Minors, and non-majors

  5. The Problem • Computer Science students view computer architecture as abstract • Just lines on a chalkboard • Difficulty visualizing information as electrical signals • Computer Organization ought to be tangible!

  6. Typical Approaches • FPGAs • Microcontrollers • Single board experimental computers Same problem: • Students isolated from hardware details

  7. Goals • Computer organization digital lab experience • Similar to engineering students • Breadboards, chips, wiring... • Focus on computer design, not just digital • They should build a computer • Complement classroom material

  8. Approach • Build a computer from discrete components • Students connect: • CPU • ROM and RAM • external interface

  9. Why "Retro"? • More exposure to hardware • Well documented, inexpensive components • 8085 CPU, 2716 EPROM • Build a "real" computer • labs replicate commercial computers from late 70s

  10. Challenges • Lack of any electrical experience • Need introductory skill-building labs • Limited Time • Can't spend time teaching test equipment • Limited Equipment • Breadboard/power supply unit, chips, wires

  11. Lab Sequence • 3 Skill-Building Labs • Wiring chips on a breadboard • Logic Gates • Memory - Traffic Light Controller • 2 labs building the computer • CPU & Memory • Interface and Software

  12. Lab 1: Wiring Chips • One-week module • Give students chips, they determine function • Teaches: • Connecting wires • Powering a chip

  13. Lab 2: Make a 2-Bit Counter • Longest lab - about 3 weeks • Components: • build 2-bit adder • build D flip flop • combine to form 2-bit counter • Students learn: • to think "electrically" • to wire meticulously

  14. Lab 3: Traffic Light • Components: • Construct a state machine modeling T-intersection • Burn transition table to ROM • Connect ROM to LEDs • Teaches: • Memory • State machines • Reinforces good wiring practices

  15. Lab 4: Simple Computer • Components: • 8085 + ROM • Program to count down from 15 • Minimum needed to see it work

  16. Lab 5: I/O • Components: • add RAM • add RS-232 port • write program to read numbers and subtract them • write Tic-Tac-Toe game

  17. Materials • Breadboards and Power Supply units • Heathikit ET-3200: available on surplus market • EPROMs & EPROM programmer • Available on eBay • Logic gates, 8085 chip, wire, LEDs • Order from electronics catalogs • Tools • nothing beyond a wire cutter & screwdriver

  18. Expected vs. Actual Response • Expected: • Resistance to hands-on experience • No test equipment = circuit failure and frustrations • Actual: • Very enthusiastic, uniformly positive response on evaluations • Lack of test equipment taught students to reason when their circuits failed

  19. Future Work • Reduce time spent on the second lab • Add an extra lab module to the course • Input/output: PS/2 keyboard, LCD or VGA display • Write a monitor program to control computer from the terminal • USB interface for drive or peripherals

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