CS 221
Computer Organization and Assembly Language Programming

Fall 2026

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Readings

• Addition:
  • IMAL: Section 1.6.1, 1.6.2
  • N2T: Section 2.1 (slides 14-33)

• Adders:
  • N2T: Chapter 1 (all slides)
  • N2T: Section 2.2.1, 2.3, 2.5 (slides 60-64, 66-end)

Description

This assignment will focus on creating digital circuits. The main tasks are:

• building and testing NWay plexers
• building and testing circuits for addition

Build the circuits described in Project 2 (except ALU, but including Mux4Way, Mux8Way, DMux4Way, DMux8Way from Project 1):

N2T: Project 2

Chapter 2 provides the contract for each circuit, i.e. description of its behavior, names and number inputs, names and state of outputs. The API is available here:

The Hack Chipset

What to Submit

Inside folder computer create folder arithmetic (with the required subfolders listed below). Zip folder arithmetic in file named arithmetic.zip and upload it to the Moodle dropbox. When arithmetic.zip is unzipped it should produce folder arithmetic with the required subfolders and files inside.

HDL/Logisim Notes

Click the thumbnail for notes on Splitter and Constant in HDL and Logisim:

Design in Logisim

Note the following requirements:

• arrange the circuits vertically in the given order (each below the previous one, *not* in a grid)
• label the input pins as specified in the contract (ok that there will be duplicate names)

Here are additional specific requirements:

• save the Logisim files in folder computer/arithmetic/circ

• see notes above on Constant and Splitter

• Mux4Way16, Mux8Way16:
  • save in files named Mux4Way16.circ and Mux8Way16.circ
  • basic gates should be avoided if possible
  • Mux4Way16 should be built primarily of Mux16; as few as possible
  • Mux8Way16 should be built primarily of Mux16,Mux4Way16; as few as possible
  • Logisim has a single Multiplexer component whose properties can be changed to have the desired number of inputs and bus widths

• DMux4Way, DMux8Way:
  • save in files named DMux4Way.circ and DMux8Way.circ
  • basic gates should be avoided if possible
  • DMux4Way should be built primarily of DMux; as few as possible
  • DMux8Way should be built primarily of DMux,DMux4Way; as few as possible
  • Logisim has a single Demultiplexer component whose properties can be changed to have the desired number of outputs and bus widths

• HalfAdder, FullAdder:
  • save in file named HalfFullAdder.circ
  • do not use within each other
  • only basic gates may be used; as few as possible

• Add16:
  • save in file named Add16.circ
  • despite the name, for the Logisim version the two inputs will be of width 6, i.e. the Adder will only add 6 bit numbers
  • the circuit should be built of Adder components (under Arithmetic) whose pins have width 1; these will represent Half/FullAdder depending on how they are used
  • basic gates should be avoided, if possible

• Inc16:
  • save in file named Inc16.circ
  • despite the name, for the Logisim version the inputs will be of width 6, i.e. the circuit will only increment 6 bit numbers
  • build with suitably sized Adder
  • basic gates should be avoided, if possible

Design in HDL

Here are additional specific requirements:

• implement one circuit at a time; for circuit X copy only X.cmp, X.tst to folder computer/arithmetic/hdl

• for each circuit click button Add File to add X.hdl (a blank file); see class examples for syntax

• see notes above on Constant and Splitter

• Mux4Way16, Mux8Way16:
  • basic gates should be avoided, if possible
  • Mux4Way16 should be built primarily of Mux16; as few as possible
  • Mux8Way16 should be built primarily of Mux16,Mux4Way16; as few as possible

• DMux4Way, DMux8Way:
  • basic gates should be avoided, if possible
  • DMux4Way should be built primarily of DMux; as few as possible
  • DMux8Way should be built primarily of DMux,DMux4Way; as few as possible

• HalfAdder, FullAdder:
  • do not use within each other
  • only basic gates may be used; as few as possible

• Add16:
  • built primarily out of HalfAdder,FullAdder
  • basic gates should be avoided, if possible

• Inc16:
  • ok to use any of the previous chips
  • basic gates should be avoided, if possible

The End