Cascading 7485 comparators for 8-bit comparison To compare two 8-bit numbers using two 7485 (4-bit) magnitude comparators, how should the cascade connections be made?

Introduction / Context:The 7485 is a 4-bit magnitude comparator with cascade inputs (<, =, >) and outputs (P < Q, P = Q, P > Q). Cascading two devices allows comparison of wider words such as 8-bit values.

Given Data / Assumptions:

• Two comparators: COMP A compares the lower-order 4 bits, COMP B the higher-order 4 bits.
• Proper use of cascade pins is required for correct multi-byte comparison.

Concept / Approach:The lower nibble determines equality and less/greater status only if the higher nibbles are equal. Therefore, the outputs from the lower comparator must feed the cascade inputs of the higher comparator. The lowest-level comparator’s cascade inputs must be initialized to “equal” true and “less/greater” false to start the chain.

Step-by-Step Solution:Assign COMP A to bits [3..0] and COMP B to bits [7..4].Initialize COMP A cascade inputs: = input = 1 (VCC), < input = 0 (GND), > input = 0 (GND).Connect COMP A outputs (P < Q, P = Q, P > Q) to COMP B inputs (<, =, >), respectively.Read the final comparison results from COMP B outputs.

Verification / Alternative check:This is the standard cascading method in the 7485 data sheet truth table and application diagrams.

Why Other Options Are Wrong:Connecting outputs to outputs (option a) is invalid and may damage parts.Option b lacks the necessary initialization of the lowest stage inputs.Option c initializes but fails to cascade the stages.

Common Pitfalls:Accidentally swapping less/greater lines or forgetting to tie initial cascade inputs, resulting in indeterminate comparisons.

Final Answer:Connect A’s P < Q, P = Q, P > Q outputs to B’s <, =, > inputs, and also tie A’s = input high (VCC) with < and > inputs low (ground).