845 4-bit ALU :: Quicker, easier and cheaper to make your own chip!

Project Datasheet: 4-Bit ALU

Overview

The 4-Bit ALU module is a digital system designed to perform various arithmetic and logical operations on 4-bit binary numbers. It supports operations such as addition, subtraction, multiplication, division, and several logical operations. Additionally, it includes an encryption function that can be used to encrypt 4-bit inputs using an 8-bit key.

How it Works

The module accepts two 4-bit binary numbers, a and b, and a 4-bit operation code (opcode) that determines the operation to be performed. The results are then output through the uo_out wire, while additional status information, such as carry out and overflow, is output through the uio_out wire. The uio_oe wire controls the enable or disable functionality for the uio_in and uio_out wires.

Operations

ADD: Adds a and b, producing a 4-bit result and a carry out.
SUB: Subtracts b from a, producing a 4-bit result and a borrow indication.
MUL: Multiplies a and b, producing an 8-bit result.
DIV: Divides a by b, producing a 4-bit quotient and remainder. Division by zero is handled by returning a zero result.
AND: Performs a logical AND operation on a and b.
OR: Performs a logical OR operation on a and b.
XOR: Performs a logical XOR operation on a and b.
NOT: Performs a logical NOT operation on a, with b being ignored.

Encryption Function

ENC: Encrypts the inputs a and b using an 8-bit key derived from concatenating a and b (treated as an 8-bit value). The encryption function applies an XOR operation between this 8-bit concatenated value and a fixed 8-bit key (KEY). The result is an 8-bit encrypted value.

Encryption Details:
- Key Generation: The key for the encryption function is a fixed 8-bit value.
- Encryption Operation: The concatenated value of a and b (forming an 8-bit value) is XORed with the fixed 8-bit key.

How to Test

To test the 4-Bit ALU module, follow these steps:

Connect Inputs:
- Connect the ui_in wire to the 4-bit inputs a and b.
- Connect the uio_in wire to the 4-bit opcode.
Connect Outputs:
- Connect the uo_out wire to an 8-bit output display or register to observe the operation result.
- Connect the uio_out wire to observe the carry out and overflow status.
Signal Management:
- Ensure the ena signal is active (high).
- Provide a clock signal to the clk input.
- Optionally, use the rst_n signal to reset the module by pulling it low.
Operation Testing:
- Cycle through various opcode values and corresponding a and b inputs to verify the correct operation of the module.
- For encryption, ensure a and b are combined and XORed with the fixed key. Verify that the result matches expected encrypted values.

#	Input	Output	Bidirectional
0	a[0]	result[0]	opcode[0]
1	a[1]	result[1]	opcode[1]
2	a[2]	result[2]	opcode[2]
3	a[3]	result[3]	opcode[3]
4	b[0]	result[4]
5	b[1]	result[5]
6	b[2]	result[6]	carry_out
7	b[3]	result[7]	overflow

845 4-bit ALU

845 : 4-bit ALU