Computer Science 220
Assembly Language & Computer Architecture

Fall 2010, Siena College

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Agenda

• Announcements
• Unix Tip of the day: alias
• Lab 4 recap
• Using Logisim
• Adding Circuits
  • Ripple carry adders
  • Subtractors
  • More efficient adders
• Sequential circuits
  • edge detection
  • clocks

Lecture Assignment 0e

Due at the start of class, Thursday, October 28.

Please submit answers to these questions either as a hard copy (typeset or handwritten are OK) or by email to jteresco AT siena.edu by the start of class. We will discuss these questions at the start of class, so no late submissions are accepted.

1. Consider a 2-bit ripple-carry adder and a direct implementation of a 2-bit adder using sum-of-products circuits (3 functions of 5 inputs). You need not construct the actual circuits, but discuss the relative costs in terms of gate count and gate delay. How do you think these change as the number of bits increases?
2. Draw a much simpler circuit that is equivalent to the following:
   
3. Occasionally it is necessary to add 1 to a number, for example, a program counter. Construct a device that is less expensive than a ripple-carry adder, that adds one to a value that is provided (D0..D3) and provides the result on the output (Q0..Q3). (Hint: you may consider a modular approach.)