ADDER8 (8-bit Adder)
Inputs
| Pin | Type | Description |
|---|---|---|
| A | bus8 | First addend (8-bit) |
| B | bus8 | Second addend (8-bit) |
Outputs
| Pin | Type | Description |
|---|---|---|
| Sum | bus8 | 8-bit sum (A + B) mod 256 |
How It Works
ADDER8 is a pre-built chip awarded upon completing level 8. It computes the 8-bit sum of two operands: Sum = (A + B) mod 256. Overflow beyond 255 is discarded — the result wraps around modulo 256.
Internal structure: a chain of 1 Half Adder (for bit 0, the LSB) and 7 Full Adders (for bits 1–7). Each stage's CarryOut feeds the next stage's CarryIn, forming a ripple-carry chain.
Usage
Reward for clearing level 8. From level 9 onward, ADDER8 is available in the component palette. It is pre-placed on the canvas for levels 13–16 (ALU construction and CPU final). Used inside the ALU to implement ADD and SUB operations, and in the Program Counter for the +1 increment.