BCD Counters — Interpreting the Term A BCD counter is best described as which type of modulus counter for digital systems?

Introduction / Context:
BCD (Binary-Coded Decimal) counters are common in time and frequency instrumentation because they align with decimal digits. Unlike pure binary counters, BCD counters restrict the state space to ten valid patterns per digit, simplifying decimal readouts on displays and printouts.

Given Data / Assumptions:

• Single BCD digit uses 4 bits to encode 0–9.
• Illegal states 1010–1111 are skipped or corrected by internal reset logic.
• Each decade stage divides frequency by 10.

Concept / Approach:
A BCD counter is, by definition, a decade counter with modulus 10. It cycles through 0000 (0) to 1001 (9) and then resets to 0000, dividing the input frequency by 10. Multi-digit BCD counters cascade decades to form decimal numbers (tens, hundreds, etc.).

Step-by-Step Solution:
Define BCD digit: 4-bit code for 0–9 only.Identify modulus: number of valid states = 10 → MOD-10.Count sequence: 0000→0001→…→1001→wrap to 0000.Therefore, a BCD counter is a decade (mod-10) counter.

Verification / Alternative check:
Examine common TTL/CMOS parts (e.g., 7490 as decade with appropriate wiring, 4510 CMOS BCD up/down): datasheets specify divide-by-10 behavior and show invalid state handling.

Why Other Options Are Wrong:

• Binary counter of unspecified modulus: Too vague; BCD specifically implies ten states.
• Full-modulus counter using all 16 4-bit combos: That would be a MOD-16 binary counter, not BCD.
• Divide-by-10 using 0000–1111: Contradiction; BCD excludes 1010–1111.

Common Pitfalls:
Assuming BCD equals binary; in BCD, some 4-bit codes are invalid and must be handled.

Final Answer:
a decade (modulo-10) counter that cycles through 0000 to 1001