Question E7A02:
What is the function of a decade counter?  

Choices:  
A: It produces one output pulse for every 10 input pulses  
B: It decodes a decimal number for display on a seven-segment LED display  
C: It produces 10 output pulses for every input pulse  
D: It decodes a binary number for display on a seven-segment LED display    

Correct Answer is  A: It produces one output pulse for every 10 input pulses  

A decade counter is a divide-by-10 counter. It counts input clock pulses from 0 to 9 (10 states), then resets and repeats. This produces one output pulse (often the “carry” or “divide-by-10” output) for every 10 input pulses.

Why the correct answer is correct (A):
- A decade counter counts modulo 10. After 10 input clocks, it rolls over and generates one output pulse.
- Frequency division: $$f_{\text{out}} = \frac{f_{\text{in}}}{10}$$

Why the other choices are incorrect:
- B: “Decodes a decimal number for a seven-segment LED” describes a BCD-to-7-segment decoder/driver (e.g., 7447, 4511), not a counter.
- C: “Produces 10 output pulses for every input pulse” implies frequency multiplication by 10. Counters divide frequency; they don’t multiply.
- D: “Decodes a binary number for a seven-segment LED display” is again a decoder/driver function, not a counter.

Useful rules of thumb:
- Decade counter = divide-by-10: $$f_{\text{out}} = \frac{f_{\text{in}}}{10}$$
- Cascading decade counters divides by powers of 10: $$f_{\text{out}} = \frac{f_{\text{in}}}{10^n}$$
- Many decade counters count 0–9 (BCD). Some (e.g., CD4017) provide 10 sequential decoded outputs, but the overall function is still modulo-10 counting/division.