HDL keypad scanner behavior In an HDL keypad-scanning application that uses a ring counter to scan columns, what should the ring counter do when a key press is detected?

Introduction / Context:
Matrix keypads are commonly scanned by activating one column (or row) at a time and reading the opposite dimension. A ring counter is ideal for generating one-hot scan patterns. Correct behavior on a key press is crucial for debouncing and stable detection.

Given Data / Assumptions:

• A ring counter cycles active columns (for example, 0001, 0010, 0100, 1000).
• Rows are read back to detect which key is pressed.
• Once a press is found, we want to capture deterministic column/row data.

Concept / Approach:
When any key closes, the current column and the detected row together identify the pressed key. If the ring counter keeps advancing, the sensed column will change during the same physical press, creating ambiguity. Freezing the ring counter stabilizes the active column while the system debounces and encodes the key.

Step-by-Step Solution:

Verification / Alternative check:
Scope the column lines and a row line: during a press, the active column should hold steady until data valid (DAV) is generated and the system acknowledges.

Why Other Options Are Wrong:

• Count to find the row/column: The ring counter scans columns; rows are sensed inputs, not counted.
• Start the D flip-flop: Flip-flops may store states, but the fundamental action needed is to freeze scanning.

Common Pitfalls:
Failing to freeze can cause ghosting or multiple detections; neglecting debounce can produce spurious keystrokes.

Final Answer:
Freeze