200 4-Bit ALU
200 : 4-Bit ALU
- Author: CE JMU Wuerzburg
- Description: A simple 4-Bit ALU which contains two types of adders, multipliers, a comparator and a barrel-shifter
- GitHub repository
- Clock: 0 Hz
How it works
The ALU contains a ripple carry adder, a carry lookahead adder, a matrix multiplier, a wallace-tree multiplier, a comparator and a barrel-shifter. Everything is implemented fully combinational. A 3-bit opcode is used to select the respective component.
How to test
No clock is required. The first 4 input bits a[3...0] form the first operand, the last 4 input bits b[3...0] form the second operand. The outputs s[7...0] are used for the compuational results, the results for shifting a, or the results of comparing a with b. The bidirectional input bits 0, 1 and 2 are used as opcode to select the component, c.f. Figure above. If the barrel-shifter is used, a[3...0] will be shifted, b[1...0] is used to specify the shift width, whereas b[2] selects the shift direction.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | a[0] | s[0] (1, if $a > b$) | opcode[0] |
| 1 | a[1] | s[1] (1, if $a < b$) | opcode[1] |
| 2 | a[2] | s[2] (1, if $a == b$) | opcode[2] |
| 3 | a[3] | s[3] | |
| 4 | b[0] | s[4] | |
| 5 | b[1] | s[5] | |
| 6 | b[2] (0 = shift right, 1 = shift left) | s[6] | |
| 7 | b[3] | s[7] |