Introduction / Context:
Magnitude comparators determine whether A < B, A = B, or A > B. For wide words (more than the base bit-width), multiple comparator slices must be chained. Control inputs enable clean multi-slice operation.
Given Data / Assumptions:
- Comparator slices operate on limited width (for example, 4 bits).
- We must compare multi-nibble or multi-byte values by cascading stages.
Concept / Approach:
Control inputs such as AB_in feed the results from less-significant stages into more-significant ones. The most-significant slice outputs the final comparison after considering these chained inputs, thereby enabling scalable word sizes.
Step-by-Step Solution:
Identify the need: compare words wider than a single comparator's width.Use control/cascade inputs to import lower-order comparison results.Produce final AB at the top stage.
Verification / Alternative check:
Datasheets for devices like the 7485 show pins named “cascade inputs” and “cascade outputs” for exactly this purpose.
Why Other Options Are Wrong:
- Generic phrases (B, C, D): Too vague and do not capture the specific purpose of cascading multi-chip comparisons.
Common Pitfalls:
- Driving cascade inputs incorrectly (for example, not setting the initial least-significant comparator inputs), which yields erroneous results.
Final Answer:
For cascading the chips
Discussion & Comments