Concept & Reasoning

A decoder with n binary inputs can represent up to 2^n input combinations. Four bits provide 16 combinations, of which the ten combinations 0000 through 1001 are valid BCD digits. The remaining six are invalid BCD codes. Thus the decoder still requires four input bits.

How to Solve It in the Exam

BCD = 8421 = four input bits.

Important Exam Point

Do not confuse number of outputs (10) with number of inputs (4).

Quick Trick

BCD = 8421 = four input bits.

Common Mistake

Answering 10 because it is a 1-of-10 decoder.

Concept & Reasoning

A decoder with n binary inputs can represent up to 2^n input combinations. Four bits provide 16 combinations, of which the ten combinations 0000 through 1001 are valid BCD digits. The remaining six are invalid BCD codes. Thus the decoder still requires four input bits.

How to Solve It in the Exam

BCD = 8421 = four input bits.

Important Exam Point

Do not confuse number of outputs (10) with number of inputs (4).

Quick Trick

BCD = 8421 = four input bits.

Common Mistake

Answering 10 because it is a 1-of-10 decoder.

Concept & Reasoning

A decoder with n binary inputs can represent up to 2^n input combinations. Four bits provide 16 combinations, of which the ten combinations 0000 through 1001 are valid BCD digits. The remaining six are invalid BCD codes. Thus the decoder still requires four input bits.

How to Solve It in the Exam

BCD = 8421 = four input bits.

Important Exam Point

Do not confuse number of outputs (10) with number of inputs (4).

Quick Trick

BCD = 8421 = four input bits.

Common Mistake

Answering 10 because it is a 1-of-10 decoder.