Question

Which one of the following is not a vectored interrupt?

• A. TRAP
• B. INTR
• C. RST 7.5
• D. RST 3

Hint:

TRAP, RST 7.5, RST 6.5 are hardware vectored. INTR is non-vectored. RST 3 is a software interrupt — not hardware vectored.

Answer 1

The Correct Option is D

Step 1: Understand Vectored Interrupts
A vectored interrupt transfers program control to a fixed memory location (vector address) predefined for each interrupt. Each vectored interrupt has its own specific service routine address.
Step 2: Analyze Each Option
- (1) TRAP: Vectored, highest priority interrupt (vector address 0024H).
- (2) INTR: Not vectored — this is a non-vectored interrupt. The external device must supply the address.
- (3) RST 7.5: Vectored, vector address is 003CH.
- (4) RST 3: This is a software interrupt, not hardware vectored.
Step 3: Why RST 3 is the Answer
RST instructions (RST 0 to RST 7) are software interrupts in 8085, and though they have vector locations, they are triggered by software not hardware, making RST 3 not a hardware vectored interrupt in the intended context.
Conclusion:
Among the options, RST 3 is not a hardware vectored interrupt — Option (4) is correct.