The World of Computing	CS100
Haverford College	Spring 2008
Lab 3	April 23

We will use PIPPIN, Rosetta and Loggo extensively. These applications are available on the web as well as on the CD-ROM from the text.

Goals:

• distinguish among high-level, assembly and machine languages
• translate introductory-level programs from one level to another
• understand the techniques of parsing and code generation
• experience with computing at distinct levels of abstraction:
  • algorithms
  • programs
  • machine code
• appreciation of the representation(s) of Boolean logic (e.g., circuits, truth tables, logic expressions)

Exercises: you are encouraged to confirm your answers using the tools from lecture and lab. For questions #6-8, note that the following Boolean (logic) expressions are equivalent:

1. convert binary 101100 to decimal
2. convert binary 101100 to hexidecimal
3. convert decimal 328 to binary
4. construct the parse tree for the statement w = x - y * z
   (it is suggested that you confirm your tree using Rosetta)
5. generate the corresponding PIPPIN assembly code for the statement from the previous question, w = x - y * z (again, you can use Rosetta, but it is also suggested that you insert the code into the PIPPIN machine and execute it to witness how the parts of the architecture interact)
6. diagram the circuit for the Boolean statement z = (a + a')b
   (it is suggested that you use Logg-o to build and simulate the logic of your circuit diagram)
7. provide the truth table for the Boolean statement from the previous question, z = (a + a')b
8. review the previous two answers, and provide a simpler version of the Boolean statement from the previous two questions, z = (a + a')b
9. write a PIPPIN assembly code program that computes the expression w = x^y, or w = x raised to the power y, where x and y are whole numbers (zero and the counting numbers). It is suggested that you first write the program using control structures from a higher level language (like Alice), and then translate it into PIPPIN. Run your code on the PIPPIN machine to make sure that it works, then take a screenshot of the window with the PIPPIN machine in its final state when the program halts

Evaluation:

• Submit a paper copy of each answer, including the code you write in #9 and a printout of the screenshot, with your name included. Please be sure this is readable, and bound (i.e., stapled, clipped) properly.

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