159.233 Computer Architecture Assignment 1
Due date 1st April 2018
Design a basic Arithmetic/Logic Unit (ALU) that operates on two 2-bit binary numbers a and b and generates a third 2-bit numbers.
The function of the ALU is determined by a 3-bit binary code f:
|
f Name Function |
|
000 XOR Logical Exclusive OR of a and b |
|
001 AND Logical AND of a and b |
|
010 ADD Add a to b (ignore cin) |
|
011 ADC Add a to b and include cin |
|
100 SUB Subtract b from a (ignore cin) |
|
101 SBC Subtract (b + cin) from a |
|
110 RSB Subtract a from b (ignore cin) |
|
111 RSC Subtract (a + cin) from b |
a0 is the least significant bit of a, a1 is the most significant bit. For operations which do not use the carry input, it should be ignored. For operations which do not generate a carry (the first two), the carry output should be zero. If a carry occurs as a result of an addition, or a borrow occurs as a result of a subtraction, then cout should be 1.
Starting with the file alu2017.lgf (available on stream) add your design and test it using the switches labelled: a0, a1, b0, b1, f0, f1, f2 and cin and the lights labelled s0, s1 and cout. Do NOT change or add anything inside the box in alu2017.lgf or use the “test” connection; if you do, you WILL lose marks. You may only use basic gates (AND, OR, NOT, XOR, NOR, NAND) with any number of inputs. You must use the connections from the alu2017.lgf file. To do this, use the ‘to’ or ‘from’ devices in the catalogue. These allow you to make connections without drawing wires, simply click to assign a name to a connection and it will be connected to all other ‘to’ or ‘from’ devices with the same name. Your connections must be called a0, a1, b0, b1, cin, f0, f1, f2, cout, s0 and s1 so that they will connect to the test circuit. Do not add any
switches to your design, you must be able to test your design by changing the switches on the left inside the box. Make sure the blue bars at the bottom of the log screen are not red before you submit your assignment.
This assignment is worth 10% of the final marks
Your assignment will be judged on accuracy and neatness. Submit your alu.lgf file electronically from stream.
Make sure your name and id are displayed in your design. Late submission – 10% per day
This is an individual assignment; marks will be deducted if your submission is similar to others.