Keyboard to BCD — identify the appropriate MSI function block A circuit must encode one of ten decimal key presses (0–9) into a 4-bit BCD output. Which MSI function best fits this requirement?

Introduction / Context:
Human interfaces like numeric keypads produce one-of-ten active signals. Digital systems commonly require a compact 4-bit binary-coded decimal (BCD) representation. Recognizing the MSI block that compresses multiple inputs into a coded output is essential in front-end design.

Given Data / Assumptions:

• Ten inputs (0–9), only one active at a time under normal operation.
• Desired output is 4-bit BCD (0000 to 1001).
• Occasional multiple activations must be resolved predictably.

Concept / Approach:
An encoder performs input compression: a one-hot input line is converted into a binary code. To handle possible simultaneous presses (two keys), a priority encoder assigns precedence (e.g., highest-numbered input) to guarantee a valid, deterministic code. Typical MSI devices include the 74147/74148 families for decimal/octal priority encoding.

Step-by-Step Solution:
Map each key line to the corresponding code (e.g., key 7 → 0111).Use a priority encoder variant to define which key wins on overlap.Buffer and debounce as needed; optionally latch the BCD code.Drive downstream display decoders or arithmetic blocks with the BCD output.

Verification / Alternative check:
Simulate multiple key-press cases; confirm priority behavior and verify exactly one valid BCD code appears at the outputs at a time.

Why Other Options Are Wrong:
A decoder expands code to many outputs (reverse function). A multiplexer selects one of many data inputs; it does not produce a code. A demultiplexer routes one input to many outputs; again, not a coder.

Common Pitfalls:
Omitting diodes or logic to prevent ghosting; ignoring key bounce and failing to latch the stable code leads to flicker or misreads.

Final Answer:
priority encoder