BusZero (Zero Detector)
Inputs
| Pin | Type | Description |
|---|---|---|
| A | bus8 | Input bus to check (8 bits) |
Outputs
| Pin | Type | Description |
|---|---|---|
| Q | bit | 1 if A = 0 (all bits zero), 0 otherwise |
How It Works
Outputs 1 when all 8 bits of input A are 0. For any non-zero value, the output is 0.
This is equivalent to an 8-input NOR gate: Q = ~(A[0] | A[1] | A[2] | A[3] | A[4] | A[5] | A[6] | A[7]).
Usage
Zero flag alternative: the ALU8 has a built-in Zero output, but BusZero provides a standalone zero check for any bus signal — not just ALU results.
Used in level 25 "Negative Check" — detect when a value is zero for conditional logic. Combine with XOR to test equality between two values: XOR(A, B) fed into BusZero yields 1 when A = B.