CS 221
Computer Organization and Assembly Language Programming

Fall 2025

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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

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

Here are a few comments on Logisim:

• Splitter: Logisim has a component called Splitter under Wiring; it can be used to split or merge wires depending on the point of view (i.e. on the orientation); it can be oriented appropriately via the Properties panel

• Constants: to achieve the effect of sending the constant value 1 to a pin in Logisim use the component 1⚬Constant under Wiring (it can also send 0)

Here are additional specific requirements:

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

• Mux4Way16, Mux8Way16:
  • save in file named Mux4Way16.circ and Mux8Way16.circ
  • Mux4Way16 should be built primarily of Mux16 (as few as possible); basic gates should be avoided if possible
  • Mux8Way16 should be built primarily of Mux16, Mux4Way16 (as few as possible); basic gates should be avoided if 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 file named DMux4Way.circ and DMux8Way.circ
  • DMux4Way should be built primarily of DMux, i.e. only 2 outputs of width 1, and selector of width 1; basic/basic16 gates should be avoided, if possible
  • DMux8Way should be built primarily of DMux, DMux4Way, i.e. only 2 or 4 outputs of width 1, and selector of width 1 or 2; basic gates should be avoided, if 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
  • only basic gates allowed

• 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); the wires of these components should have width 1
  • 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 a few comments on HDL:

• Splitter:
  • to achieve the effect of splitting wires in HDL you write:
    • gatepin=wire[i..j] or gatepin[i..j]=wire (widths have to match)
    • gatepin[i]=wire[j] or gatepin=wire[j] or gatepin[i]=wire (for 1-bit versions)
    • gatepin[i..j]=wire[p..q] (widths have to match)
    • gatepin could be an input or output pin of the gate

• Constants: to achieve the effect of sending the constant values 1 or 0 to a pin in HDL you write gatepin[?]=true or gatepin[?]=false (the ? is the index or range of indices to set)

Here are additional specific requirements:

• Implement one circuit at a time. For circuit X copy X.hdl, X.cmp, X.tst to folder computer/arithmetic/hdl.

• Mux4Way16, Mux8Way16:
  • Mux4Way16 should be built primarily of Mux16 (as few as possible); basic gates may be used if useful
  • Mux8Way16 should be built primarily of Mux16, Mux4Way16 (as few as possible); basic gates should be avoided, if possible

• DMux4Way, DMux8Way:
  • DMux4Way should be built primarily of DMux (as few as possible); basic gates may be used if useful
  • DMux8Way should be built primarily of DMux, DMux4Way (as few as possible); basic gates should be avoided, if possible

• HalfAdder, FullAdder: only basic gates may be used

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

• Inc16:
  • use Adder16
  • basic gates should be avoided, if possible

What to turn in

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.