How it works
8-Bit ALU with state machine to read A and B inputs using the 8 digital pins.
Operation control over the In/Out pins.
Status out over the In/Out pins.
Overview
This project implements an 8-bit Arithmetic Logic Unit (ALU) capable of performing operations on two 8-bit inputs (A and B).
The design uses a Finite State Machine (FSM) to control input reading, calculation, and result/status output.
Supported Operations
The ALU supports the following 7 operations:
| Operations |
| A |
| NOT A |
| A AND B |
| A OR B |
| A XOR B |
| A + B |
| A - B |
Control Logic
Inputs are read sequentially using an FSM with dedicated states for reading operands and producing outputs.
FSM States
| State |
S0 |
S1 |
| READ_A |
0 |
0 |
| READ_B |
0 |
1 |
| CALC |
1 |
0 |
| STATUS |
1 |
1 |
- READ_A – reads the first operand
A
- READ_B – reads the second operand
B
- CALC – performs the selected ALU operation
- STATUS – outputs extended status information about the result
Operation Control
Operations are selected using the f[4:0] control inputs from bidirectional pins.
| Operation |
F0 |
F1 |
F2 |
F3 |
F4 |
| A |
0 |
0 |
0 |
0 |
1 |
| NOT A |
1 |
0 |
0 |
0 |
1 |
| A AND B |
0 |
1 |
0 |
0 |
0 |
| A OR B |
0 |
1 |
0 |
0 |
1 |
| A XOR B |
0 |
1 |
0 |
1 |
0 |
| A + B |
0 |
1 |
0 |
1 |
1 |
| A - B |
0 |
1 |
1 |
0 |
0 |
ALU Status Flags
| Flag Name |
Binary Value |
Description |
| DEFAULT_FLAG |
00 |
Default state, no special condition |
| ZERO_FLAG |
01 |
Result of the operation is zero |
| NEGATIVE_FLAG |
10 |
Result is negative |
| OVERFLOW_FLAG |
11 |
Arithmetic overflow occurred |
Top-Level I/O
| Signal |
Dir |
W |
Description |
clk |
in |
1 |
System clock |
rst_n |
in |
1 |
Async reset (active-low) |
ena |
in |
1 |
Always '1' on TinyTapeout |
ui_in[7:0] |
in |
8 |
Inputs for reading A and B operators |
uo_out[7:0] |
out |
8 |
Outputs displaying result and status of ALU |
uio_in[7:3] |
in |
5 |
F0-F4 Control Keys |
uio_in[2] |
in |
1 |
Carry/Borrow Input |
uio_out[7:0] |
out |
8 |
Unused - set to '0' |
uio_oe[7:0] |
out |
8 |
set to '0' using uio as inputs |
How to test
- Set status READ_A or READ_B to read A and B operators
- Set the operation using the f[] birectional inputs
- Set status CALC, ALU peroforms operation and displays result
- Set status STATUS do display ALU status flag and carry/borrow out
