CS计算机代考程序代写 Hive Assignment 6 – COMP 273 Page 1 of 3

Assignment 6 – COMP 273 Page 1 of 3

ALU

COMP 273 Assignment 6 – Fall 2021

Submission instructions

All work must be your own and must be submitted to myCourses. Include your name and student

number in a comment at the top of your documents / Logisim circuits. Submit only one file: a6.circ. Do

not use a zip archive. Check your submission by downloading it from myCourses and checking that it was

correctly submitted. You will not receive marks for work that is incorrectly submitted.

Purpose

• Learning about the basic circuitry in the ALU

• To get used to 2’s complement

• To get used to using flags

Helpful

• A5 should be completed before you start this assignment

• The lecture recordings on CPU.

• Assuming you have completed A5, this assignment should take about two days to complete.

• There will be an extra tutorial for using Logisim this week (Logisim Help Desk).

Assignment 6 – COMP 273 Page 2 of 3

Implementation

Using Logisim Evolution create the circuit for the following problem:

Figure 1: High-level view of ALU

– Task: Build the circuit (blue boxes) of figure 1.

– Inputs: L and R (nibble sized, 4 pins each), plus Add/Subtract command pin.

– Outputs: A-out (nibble sized, 4 pins) and Status (3 pins)

– Circuits: 2’s complement circuit, adder circuit, and status output circuits. Plus, a CLOCK.

NOTE: Your final circuit does not need to look exactly like figure 1. However, the input and output pins

must look like figure 1.

NOTE 2: Your final circuit must use designs we covered during class. You cannot use any outside (other

sourced) circuit designs.

NOTE 3: You must build the circuit from the following components ONLY: wires, clock, AND, OR, NOT,

pins, and XOR. You CANNOT use: any prebuilt adder circuits, or any other prebuild items from Logisim.

Optionally you can use: tunneling and “adding a circuit” from the project menu.

Steps

• Begin by placing the input and output pins onto the circuit. These pins will be used to enter and

see values.

• Do not use registers for: L, R, A-out, Status, and the command pin.

• The Adder circuit assumes two 2’s compliment inputs in L and R. The L input goes directly into

the Adder without modification. The R input goes through the 2’s complement circuit and may

modify R’s value (for example, R may be 5, but the 2’s complement circuit changes it to -5). The

solution to the addition is outputted to the A-out pins.

• The 2’s complement circuit is controlled by the command pin and will negate the 2’s

complement R input value when commanded to do so during subtraction. Otherwise, during

Adder

2’s

complement

Status

determi-

nation

Assignment 6 – COMP 273 Page 3 of 3

addition it simply lets the R value pass through without change. When the command pin is 0 the

ALU is performing an addition. When the command pin is 1 the ALU is performing a subtraction.

• The Status register’s flag bits are updated by the result stored in A-out. Bit 0 = negative, Bit 1 is

zero, and bit 3 is overflow.

• Add a clock to control the execution of this circuit.

Execution

Your ALU circuit must be able to do the following:

1. 0 – 0

2. 1 – 1

3. 1 – (-1)

4. 2 – 1

5. 1 – 2

6. Overflow

7. And the other numbers that fit within the 2’s compliment nibble.

Note: The TA will input the numbers into the L and R pins in 2’s complement form by hand.

Marking

• Maximum 20 points

o +7 Adder circuit

o +7 2’s complement circuit

o +6 Status determination circuits

• -10% per day late with max 2 late days

• -3 points for not following instructions

• -5 points for not using the clock

• Assignment must execute to be graded