Major building blocks of an HDL keypad emulator When emulating a matrix keypad in HDL, which major block is essential for generating the one-hot scanning pattern that steps through columns?

Introduction / Context:Keypad emulation or scanning requires driving one column at a time while monitoring rows for closures. HDL designs accomplish this with a compact pattern generator to step through columns in a loop.

Given Data / Assumptions:

• Matrix keypad with multiple rows and columns.
• Goal is to minimize simultaneous column drive to avoid ghosting.
• Need a deterministic, cyclic one-hot pattern.

Concept / Approach:A ring counter is perfect for producing a circulating one-hot vector (for example, 0001 → 0010 → 0100 → 1000 → 0001 ...). This directly drives columns and simplifies the logic required to identify the active column during a key press.

Step-by-Step Solution:

Verification / Alternative check:Simulate the ring counter sequence and confirm only one column is asserted at a time. In hardware, LEDs on columns will “walk” visibly.

Why Other Options Are Wrong:

• Sequencer: Sometimes used generically, but the specific, efficient block is a ring counter.
• Clock: Necessary, but not the scanning logic itself.
• Multiplexer: Useful for routing signals, not for generating the one-hot pattern.

Common Pitfalls:Forgetting to handle rollover or to synchronize row sampling to avoid metastability; not freezing the scan during a press.

Final Answer:A ring counter