ALU Help

Hey,

I think I can help you a little bit because I am actually doing the same project right now, though I have not finished making all my parts.

So, assuming you built all your individual functions correctly and according to your assignment specifications then all you need is a way to select which function to use. ALUs calculate all the functions at once and then select which one to use based on the instruction. Using the results of your different functions as inputs, a multiplexer (mux) can be used with a 3 or 4 bit selection line depending on how you set up your functions. Each binary number can represent a different function. The output of the mux will then be the result of the function of the two inputs that you selected.

What coding language are you using? For example, VHDL, Verilog, etc.

Hmm, well I do not use UI based systems for digital design, but it should be a similar process to coding. First, make sure all your individual functions work properly by testing them in waveform simulations. Each function should have its own file. Then to make the ALU, open a new file and insert the circuits for all the other functions and insert the mux. Then just connect all your signal lines. You should be able to simulate this with waveforms also.

A lot of programs have project files to store all the device files you have made. When you insert a device into a file you usually reference it and assign the inputs and outputs. At simulation time, the software you use will call each individual component you referred to and be able to simulate a large device, such as the ALU.

If you this is not helpful to you, then you should ask a student in your class or a professor about how to use the software. I do not know how to use your software.

Let me give you an example, this might be more helpful.

module ALU(A,B,C,E);
// the ALU device has input A, input B, output C, and select line E
input [63:0]A,B;
// A and B are 64 bits long
input [2:0]E;
// the select line is 3 bits, base 10 number '0-7'
output [63:0]C;
// C is 64 bits long
wire [63:0]Cxor,Cand,Cor,Cshift,Cneg,Caddsub;
// these wires are 64 bits long each and they are used to connect the output of each function to the input of the ALU's mux
wire Co;
// this wire is 1 bit long and used as the carry from the add or subtract functions

AddSub_64bit unit1(A,B,E[0],Co,Caddsub);
// this calls my add/subtract device using the signals from the ALU and the wires mentioned before
// the E[0] refers to the most significant bit of my select signal for the mux to make my adder add ,0, or subtract ,1
AltShifter unit2(A,B,Cshift,E[1]);
// this calls my shifter and makes in the same way as the other device
// the E[1] refers to the middle bit of the select line and is used to make my shifter shift left ,0, or shift right ,1
and_64bit unit3(A,B,Cand);
// this calls my AND device with input and outputs assigned like the pervious devices
// all my other devices are listed the same way, but I omitted them


// Two lines of code go here, but I omitted them

// to select each function based on the select line I used a case statement
// '0-7' are the base 10 numbers for the 3 bit binary select line E
// my guess is that UI program would just assign selection numbers from the lines connected from top to bottom, 0 to the max value
case(E)
0:C=Caddsub;
1:C=Cand;
2:C=Cor;
3:C=Cxor;
4:C=Cshift;
5:C=Cneg;
6:C=Cshift;
7:C=Caddsub;
// C, the output of the ALU, is assigned the value of the selected function based on the select line
// for example, the ALU will output 'A AND B' when the select line is '001' in binary

// two other lines of code were omitted here


Basically you have do something like this, but you just draw the lines and insert devices instead of writing code.

pleaseee help me

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