32 8-bit Interactive ALU :: Quicker, easier and cheaper to make your own chip!

32 : 8-bit Interactive ALU

Author: Matanel Kadosh

Description: An 8-bit Arithmetic Logic Unit with internal registers and multiplexed output for result/carry.

Clock: 10000000 Hz

How it works

This project is an 8-bit Interactive Arithmetic Logic Unit (ALU) designed for real-time calculation and hardware verification. The core is built around a two-register architecture (Register A and Register B) and can execute 11 different mathematical and logical operations based on a 4-bit opcode.

To maximize the efficiency of the physical pins and fit within the standard Tiny Tapeout 3x PMOD footprint, the design implements an Output Multiplexer:

The internal ALU calculates a 9-bit result to capture overflow/carry.
The 8-bit output bus (uo_out) is multiplexed.
By toggling the Out_Sel control pin, the user can switch the output bus to display either the 8-bit numerical result or the 9th bit (Carry Flag) on the LSB of the output bus.

The control bus is routed through the bidirectional pins (uio_in), which are hardware-locked to act strictly as inputs for safety.

How to test

The ALU is designed to be driven by a microcontroller or a Raspberry Pi.

Initialization: Assert the rpi_reset pin (uio_in[7]) HIGH to clear the internal registers.
Load Data: Apply an 8-bit value to the input data bus (ui_in). Pulse Load A (uio_in[0]) or Load B (uio_in[1]) HIGH then LOW to latch the data into the respective internal registers.
Execute: Apply a 4-bit opcode to ALU_OP (uio_in[5:2]). The ALU processes the operation combinationally.
Read Result: * Set Out_Sel (uio_in[6]) to 0 and read the 8-bit result on the output bus (uo_out).
- Set Out_Sel to 1 and read uo_out[0] to check for an Arithmetic Carry or Overflow.

Supported Opcodes:

0000: AND
0001: OR
0010: ADD (with Carry Out)
0011: SUB
0100: XOR
0101: NAND
0110: NOR
0111: Shift Left
1000: Shift Right
1001: NOT A
1010: NEG A (2's Complement)

External hardware

To fully interact with and verify the ALU, the following external hardware is recommended:

Host Controller: A Raspberry Pi, Arduino, or any 3.3V microcontroller to drive the input data and control pins.
Logic Analyzer: Highly recommended for debugging and verifying the timing of control signals (Load triggers, Opcodes) and the output bus during operation.
Connectivity: Standard PMOD cables/jumpers to connect the host controller and testing equipment to the Tiny Tapeout demo board.

#	Input	Output	Bidirectional
0	Data In Bit 0 (LSB)	Result Bit 0 / Carry Flag (When Out_Sel=1)	Load A (Trigger)
1	Data In Bit 1	Result Bit 1	Load B (Trigger)
2	Data In Bit 2	Result Bit 2	ALU_OP [0]
3	Data In Bit 3	Result Bit 3	ALU_OP [1]
4	Data In Bit 4	Result Bit 4	ALU_OP [2]
5	Data In Bit 5	Result Bit 5	ALU_OP [3]
6	Data In Bit 6	Result Bit 6	Out_Sel (0=Result, 1=Flags)
7	Data In Bit 7 (MSB)	Result Bit 7 (MSB)	Reset (Active High)

Input

Output

Bidirectional

Data In Bit 0 (LSB)

Result Bit 0 / Carry Flag (When Out_Sel=1)

Load A (Trigger)

Data In Bit 1

Result Bit 1

Load B (Trigger)

Data In Bit 2

Result Bit 2

ALU_OP [0]

Data In Bit 3

Result Bit 3

ALU_OP [1]

Data In Bit 4

Result Bit 4

ALU_OP [2]

Data In Bit 5

Result Bit 5

ALU_OP [3]

Data In Bit 6

Result Bit 6

Out_Sel (0=Result, 1=Flags)

Data In Bit 7 (MSB)

Result Bit 7 (MSB)

Reset (Active High)

Chip location

32 8-bit Interactive ALU