Keypad encoder implementation detail: In a VHDL-based keypad encoder, the ring counter that sequences the column scan is typically implemented inside a ________ that is sensitive to the clk input.

Introduction / Context:
Keypad encoders commonly scan columns or rows using a ring counter. In VHDL, sequential logic that changes on clock edges is usually described inside a clocked process. Understanding which VHDL construct is used to update a ring counter helps learners write synthesizable and predictable code.

Given Data / Assumptions:

• The keypad encoder cycles through column lines using a ring counter (one-hot sequence).
• Updates occur on rising or falling edges of clk.
• We need a construct that can hold state (registers/flip-flops).

Concept / Approach:
In VHDL, a PROCESS block with a clock in its sensitivity list or an explicit rising_edge(clk) test is the standard way to describe synchronous logic. Inside that process, one might use a CASE statement to choose next-state behavior, but CASE itself is not the container that reacts to the clock; the PROCESS is. SIGNAL is a data object, and FUNCTION is a subprogram for combinational transformations, not a clocked storage element.

Step-by-Step Solution:

Verification / Alternative check:
Most vendor coding guidelines recommend a single clocked PROCESS per register group for portability and predictable synthesis. Post-synthesis schematics show flip-flops inferred from the process.

Why Other Options Are Wrong:

Common Pitfalls:
Placing the clock in a combinational process sensitivity list; inferring latches instead of flip-flops due to incomplete assignments; mixing async and sync logic inadvertently.

Final Answer:
PROCESS