Incompletely specified functions
Functions of n inputs have 2n possible input configurations
- Some input combinations may be unused
- Unused input combinations are called �don�t cares�
- We exploit don�t cares during logic minimization
- Don�t care ? no output
Example: A binary coded decimal (BCD) function
- BCD encodes the decimal digits 0�9 as 00002�10012
- We don�t care about the binary numbers 10102�11112
- Consider a function that takes a BCD input and computes the next number in sequence
- If the input is 00102, the output is 00112
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