CS 221
Computer Organization and Assembly Language Programming

Spring 2023

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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 Mux4Way16, Mux8Way16, 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.

Design in Logisim

Note the following requirements:

• create empty folder cs221/02/ and save the Logisim files there
• arrange the circuits one after the other in the given order
• label the input pins as specified in the contract
• the topmost output pin of each circuit should include its given name and the name of the circuit:

  for example, for And16 the topmost pin will be named out_And16

Here are additional specific requirements:

• Splitter: Logisim has a component called Splitter under Wiring; it actually 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 be followed by Not if the constant 0 is needed

• Mux4Way16, Mux8Way16:
  • save in file named MuxNWay16.circ
  • Mux4Way16 should be built primarily of Mux16, i.e. only 2 inputs of width 16, and selector of width 1; basic/basic16 gates should be avoided if possible
  • Mux8Way16 should be built primarily of Mux16, Mux4Way16, i.e. only 2 or 4 inputs of width 16, and selector of width 1 or 2; basic/basic16 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
  • in each case the selector of the circuit under construction should be a single input component that is split immediately into the appropriate number of lines/widths (use Splitter under Wiring)

• DMux4Way, DMux8Way:
  • save in file named DMuxNWay.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/basic16 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
  • in each case the selector of the circuit under construction should be a single input component that is split immediately into the appropriate number of lines/widths (use Splitter under Wiring)

• 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
  • the circuit should have only two input components of width 6 (one each for a, b) that are immediately split into individual wires (use Splitter under Wiring)
  • the circuit should use a single output component of width 6 that merges the individual internal output wires (use Splitter under Wiring, oriented appropriately)
  • basic gates may be used if useful

• 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
  • option 1: ok to build with suitably sized Adder
  • option 2: ok to build of Adder components (under Arithmetic); the wires of these components should have width 1
  • the circuit should have a single input component of width 6 that is immediately split into individual wires (use Splitter under Wiring)
  • the circuit should use a single output component of width 6 that merges the individual internal output wires (use Splitter under Wiring, but oriented appropriately)
  • see above how to set a pin to a constant value
  • basic gates may be used if useful

Design in HDL

Note the following additional requirements:

• in folder cs221/02/ copy one at a time the starter code for the required circuits
• copy to folder cs221/02/ the following files:
  • Mux4Way16.(hdl|tst|cmp), Mux8Way16.(hdl|tst|cmp)
  • DMux4Way.(hdl|tst|cmp), DMux8Way.(hdl|tst|cmp)
  • do not copy any of the Mux/DMux files that were built in Project 1
• if there is an empty or incorrect circuit in the current folder it will affect other circuits that depend on it

Here are additional specific requirements:

• Splitter: to achieve the effect of splitting wires in HDL you write gatepin=wire[i..j] or gatepin[i..j]=wire (the widths have to match)

  more generally, you can write gatepin[i..j]=wire[p..q] (the widths have to match), but this general version will not be needed for this assignment

  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 (should work regardless of pin width)

• Mux4Way16, Mux8Way16:
  • Mux4Way16 should be built primarily of Mux16, i.e. only 2 inputs of width 16, and selector of width 1; basic/basic16 gates may be used if useful
  • Mux8Way16 should be built primarily of Mux4Way16, i.e. only 4 inputs of width 16, and selector of width 2; basic/basic16 gates may be used if useful

• DMux4Way, DMux8Way:
  • DMux4Way should be built primarily of DMux, i.e. only 2 outputs of width 1, and selector of width 1; basic/basic16 gates may be used if useful
  • DMux8Way should be built primarily of DMux4Way, i.e. only 4 outputs of width 1, and selector of width 2; basic/basic16 gates may be used if useful

• HalfAdder, FullAdder: only basic gates may be used

• Add16: built primarily out of HalfAdder, FullAdder; basic gates may be used if useful

• Inc16:
  • option 1: ok to build with Adder16
  • option 2: ok to build primarily out of HalfAdder, FullAdder; basic gates may be used if useful
  • see above how to set a pin to a constant value

Modify and test the respective .hdl files given by the authors that you copied from projects/02/ to cs221/02/:

• Win users: could use Notepad (shows line numbers at bottom right)
• Mac users: could use TextEdit, ensure file is edited and saved in Plain Text: "Format Menu:Make Plain Text"

What to turn in

Zip folder 02/ in file named 02.zip and upload it to the Moodle dropbox.