Question

Which of the following are interrupt inputs of 8085 microporcessor?
A. TRAP
B. RST 7.5
C. RST 10.5
D. RST 5.5
E. INTR
Choose the correct answer from the options given below:

• A. A and E only
• B. B, C and D only
• C. A, B, D and E only
• D. A, C and E only

Hint:

To remember the 8085 interrupts, memorize the sequence: TRAP, RST 7.5, RST 6.5, RST 5.5, INTR.
TRAP is non-maskable (highest priority), while the others are maskable.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
An interrupt is a signal sent to the microprocessor by an external device to temporarily halt the current program and execute a special service routine (Interrupt Service Routine).
The Intel 8085 microprocessor has 5 hardware interrupt inputs.

Step 2: Detailed Explanation:
Let us list the five hardware interrupt pins of the 8085 microprocessor in order of their priority:
1. TRAP (Non-Maskable Interrupt): Highest priority interrupt. It cannot be disabled by software. (Statement A is correct).
2. RST 7.5 (Restart 7.5): A vector, maskable interrupt triggered by a rising edge. (Statement B is correct).
3. RST 6.5 (Restart 6.5): A vector, maskable level-triggered interrupt. (Not listed in statements).
4. RST 5.5 (Restart 5.5): A vector, maskable level-triggered interrupt. (Statement D is correct).
5. INTR (Interrupt Request): Lowest priority interrupt. It is a non-vectored, maskable interrupt that requires external hardware to provide the interrupt instruction. (Statement E is correct).
Let us evaluate statement C:
- RST 10.5: There is no such hardware interrupt pin or software interrupt in the 8085 instruction set. The valid RST interrupts are RST 5.5, 6.5, and 7.5. Thus, statement C is incorrect.
Therefore, the correct interrupts are A, B, D, and E.

Step 3: Final Answer:
The correct option is (C).