ALU with function
Programmable 1-bit ALU
In this experiment, an Arithmetic and Logic Unit (ALU) capable of performing 4 Arithmetic/Logic functions on 1-bit operands, will be designed, assembled and tested. The circuit will consist of one 4-input multiplexer, one full adder, one 2 input AND gate, one 2 input OR gate and one 2-input XOR gate, all belonging to the TTL family.
ALU Function Table
| S1S0 | ALU Function | Carry | output |
|---|---|---|---|
| 00 | sum | carry | (A+B)%2 |
| 01 | A AND B | - | A & B |
| 10 | A OR B | - | A | B |
| 11 | A EXOR B | - | A ^ B |
Some important points to note are:
- S1 and S0 are select lines that select which operation should be performed by the ALU. These selection lines combined with input arguments and the functions form an Instruction Set.
- These instruction are useful in creating programs and are normally stored in a ROM unit as they are required to be used often.
- Inputs A, B are usually stored in internal registers. These, along with other special registers constitute the registers of a microcontroller.