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CS 240 Lab 4

Learning Goals & Reflection

CS 240 Lab 4

Learning Goals

Core Goals

Students can:

  1. Explain the design and operation of an Arithmetic Logic Unit:
    1. Explain how an ALU can perform multiple different operations, and which inputs control which operation it performs.
    2. Explain how multiplexers are used to control input inversion in an ALU.
    3. Explain how input inversion and carry-in can be used to implement subtraction, NAND, and NOR using an ALU that only has chips for OR, AND, and addition.
    4. Build a simulated ALU using basic logic gates, an adder, and multiplexers.
    5. Fill out the truth table for an ALU.
    6. Debug a simulated ALU by testing its outputs against a truth table.
    7. Explain how a multi-bit ALU can be constructed from a series of 1-bit ALUs, including how to connect the control lines.
    8. Design and implement the sign, overflow, and zero outputs from a multi-bit ALU.
  2. Explain how Latch and Flip-Flop circuits work:
    1. Define bistable and give an example of a bistable circuit.
    2. Build an SR latch in a simulator using two NOR gates.
    3. Explain why the output of an SR latch is not always predictable, including what sequence of events triggers unpredictable behavior and the ways that behavior can resolve itself in practice.
    4. Build an SR latch on the workbench by wiring together NOR gates in a 7402 chip.
    5. Add AND gates to an SR latch to create a clocked SR latch, both in simulation and on the workbench.
    6. Explain the purpose of a “clock” signal within a memory system.
    7. Explain why a D latch is preferable to an SR latch.
    8. Implement a D latch in a simulator using AND, NOR, and NOT gates.
    9. Explain the difference between a D latch and a D flip-flop.
    10. Implement a D flip-flop in a simulator using two D latches.
    11. Explain the difference between a rising-edge and a falling-edge trigger.
  3. Explain the operation of a register:
    1. Explain how multiple D flip-flops should be connected to create a register file.
    2. Give an example of the circuit diagram notation for a multi-wire bus, and explain what it means.
    3. Explain what happens when a register file is read from and written to at the same time in a single clock cycle.
  4. Explain the operation of a register file:
    1. Explain what the CLR and CLK inputs to a register file do.
    2. Explain how to write data into or read data from a particular register in a register file.

Stretch goals

  1. Explain how Latch and Flip-Flop circuits work:
    1. Explain why the fact that the output of a D flip-flop doesn’t change until the falling edge of the clock is useful in a system where many D flip-flops are used.
    2. Explain what would happen if D latches were used in place of D flip-flops for a register file if we want to read from that register file and write a result back into it in the same clock cycle.
  2. Explain the operation of a register file:
    1. Explain how multiple registers are connected to create a register file, including how a decoder and several multiplexers are used within the register file.

Extra goals

  1. Explain how an ALU and Register File fit together:
    1. Explain which outputs from a register file should attach to which inputs of an ALU (and vice versa) to allow for a system that can do math and store the results.
    2. Explain what additional inputs need to be specified in order to determine what the register file + ALU combination will do.
    3. Explain why the “Clock” input of the register file needs to be toggled for this system to work, and what happens when that clock input is toggled.

Reflection

Fill out the CS 240 Lab Reflection form to complete today’s lab reflection.