The three outputs x1, x2, and x3 from an 8×3 priority encoder are used to form…
2015
The three outputs x1, x2, and x3 from an 8×3 priority encoder are used to form a vector address of the form 101x1x2x300. For this vector table, take the highest-priority entry as encoder code 000 and increase the codes in binary order. What is the second-highest-priority vector address in hexadecimal?
Answer: B. A4 — ConceptA priority encoder represents the selected priority level with a binary code. When a vector-address format is specified, the complete address is…
- A.
BC
- B.
A4
- C.
BD
- D.
AC
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Correct answer: B
Concept
A priority encoder represents the selected priority level with a binary code. When a vector-address format is specified, the complete address is obtained by concatenating the fixed prefix, the encoder code, and the fixed suffix.
For an 8×3 encoder there are eight 3-bit codes, from 000 through 111. Under the convention stated in the question, the highest-priority entry receives 000 and the next entry receives 001.
Application
The first (highest-priority) vector uses encoder code 000, so the second-highest-priority vector uses 001.
Insert 001 into the format 101x1x2x300 to obtain 10100100.
Group the binary address into nibbles: 1010 0100.
Convert the nibbles to hexadecimal: 1010 is A and 0100 is 4, giving A4.
Cross-check
The fixed suffix requires the final two bits to be 00, and A4 expands back to 10100100. Its middle three bits are 001, exactly the code assigned to the second entry.
Option-value comparison
Value | Binary form | Encoder field | Suffix |
|---|---|---|---|
BC | 10111100 | 111 | 00 |
A4 | 10100100 | 001 | 00 |
BD | 10111101 | 111 | 01 |
AC | 10101100 | 011 | 00 |
Result
Therefore, the second-highest-priority vector address is A4.