TTL Counter ICs — 7490 vs. 7493 What is the key difference in modulus between the TTL counters 7490 and 7493?

Introduction / Context:
Classic 74xx counters provide fixed divide ratios without extra logic. Selecting the correct device for a decade or binary division requires knowing each chip’s modulus. Two frequently referenced parts are the 7490 and 7493.

Given Data / Assumptions:

• 7490: commonly used as a decade counter.
• 7493: commonly used as a binary divide-by-16 counter.
• Standard wiring per datasheets is assumed.

Concept / Approach:
Modulus (MOD-N) indicates how many input pulses occur per full cycle of the counter and equals the frequency division factor. The 7490 provides MOD-10 (decade). The 7493 is a 4-bit binary (MOD-16) counter. They are often cascaded to form higher decimal or binary divisions respectively.

Step-by-Step Solution:
Identify 7490 behavior: decade sequence 0–9 then reset → divide-by-10.Identify 7493 behavior: binary 0–15 then wrap → divide-by-16.Map to choice: 7490 MOD-10, 7493 MOD-16.Hence, option A is correct.

Verification / Alternative check:
Back-of-envelope: cascade four 7490 decades → decimal clocks; cascade N 7493s → binary scalers of 2^(4N). Datasheets confirm the intended moduli.

Why Other Options Are Wrong:

• Other pairings swap or misstate the true moduli.

Common Pitfalls:
Confusing 7492 (divide-by-12) with 7493 (divide-by-16); both are popular but serve different roles.

Final Answer:
7490 is a MOD-10, 7493 is a MOD-16