Computer Science 237
Computer Organization

Williams College
Fall 2005

Lecture 9: Digital Logic, Combinational Circuits
Date: September 28, 2005

Announcements

We still hate cortland. Hopefully the Unix lab is working out for everyone this week.
Lab 3 continues. Use BRK and DEB directives. If you change your logic for the assembly version, try it out in equivalent C. Come see my C solution for ideas.
No office hours Friday. But I will be around quite a bit on Thursday.

Agenda

Introduction to Logic
- Some basic electronics
- The inverter
- Notions of gate delay, signal propagation, loading, transistor/gate budgets.
- The NAND and NOR gates; then AND and OR gates.
- Universality of certain gates.
- Laws.
  - Identity, commutative, distributive, associative laws.
  - Logarithmic gate delay for fan-in of n; linear cost.
  - deMorgan's: notion of inverted logic
- Question: How do you build an XOR gate? Is it universal?
- Generation of all combinational functions (functions that are determined by inputs only).
Some new, useful functions.
- MUX's and DMUX's.