Decoder notation in IEEE/ANSI symbols A logic symbol shows the internal designation “bcd/dec”. In digital electronics, what does this indicate about the decoder’s function and its input–output size?

Introduction / Context:
Decoder symbols in the IEEE/ANSI standard often include short internal designations that summarize the input code and the output code. Understanding these tags is essential when reading schematics quickly and selecting the correct integrated circuit for tasks such as driving numeric displays or selecting one of many lines.

Given Data / Assumptions:

• The internal tag on the logic symbol is “bcd/dec”.
• We are dealing with common combinational decoders used in digital systems.
• Binary Coded Decimal (BCD) uses four input bits to represent decimal digits 0–9.

Concept / Approach:

Notation of the form “input/output” indicates the coding at the input and the coding at the output. Thus “bcd/dec” literally means the device accepts BCD and outputs decimal. A BCD-to-decimal decoder takes a 4-bit BCD input (A3..A0) and asserts exactly one of ten outputs (Y0..Y9) corresponding to the decimal digit, which is ideal for driving a 10-line interface such as a Nixie/indicator or for one-of-ten selection.

Step-by-Step Solution:

Verification / Alternative check:

Classic parts such as 7442/7445 are BCD-to-decimal decoders. Their datasheets show 4 inputs and 10 mutually exclusive outputs, matching the interpretation of “bcd/dec”.

Why Other Options Are Wrong:

• Decimal-to-BCD (options a and c) reverses the direction; that would be an encoder, not a decoder.
• “Ten inputs and four outputs” (options a and b) is the wrong sizing; decoders expand lines, not compress them.

Common Pitfalls:

• Confusing decoders with encoders; decoders generally expand N inputs to up to 2^N (or 10) outputs.
• Overlooking that BCD uses only ten of the sixteen 4-bit combinations; the remaining codes are invalid.

Final Answer:

BCD-to-decimal decoder with four inputs and ten outputs.