Counter ICs — 7490 vs. 7492 Modulus Identify the correct modulus (divide-by value) for each of these TTL counters: 7490 and 7492.

Introduction / Context:
The classic 74xx counter family contains dedicated divide-by-N counters wired internally for common moduli. Recognizing the default modulus helps when selecting parts for decade or divide-by-12 functions without external gating logic.

Given Data / Assumptions:

• Both parts are BCD/binary ripple counters with internal resets wired for a specific modulus.
• 7490 is historically known as a decade counter.
• 7492 is a divide-by-12 counter.

Concept / Approach:
A MOD-N counter repeats its count every N pulses and divides the input frequency by N. The 7490 internally implements MOD-10 (decade). The 7492 is internally configured as MOD-12, saving glue logic where divide-by-12 is needed (e.g., timebases).

Step-by-Step Solution:
Identify 7490: decade counter → MOD-10.Identify 7492: divide-by-12 counter → MOD-12.Map to answer choice: “7490 is MOD-10, 7492 is MOD-12.”

Verification / Alternative check:
Standard TTL datasheets list the 7490 as “Decade (MOD-10) counter” and the 7492 as “Divide-by-12 counter,” confirming the selection.

Why Other Options Are Wrong:

• Options A, B, C swap or misstate the moduli.

Common Pitfalls:
Confusing 7492 (MOD-12) with 7493 (binary MOD-16). The 7493 is the common divide-by-16 ripple counter.

Final Answer:
7490 is a MOD-10, 7492 is a MOD-12