In an Intel 8085 microprocessor, how many dedicated hardware interrupt input lines are available for external interrupt requests?

Introduction / Context:
This question checks basic knowledge of the interrupt structure of the Intel 8085 microprocessor. Interrupts allow external devices to request service from the CPU asynchronously and are a key part of real time and embedded system design. The 8085 has a small but important set of dedicated hardware interrupt lines, and remembering their number and names is a common requirement in viva and written exams.

Given Data / Assumptions:

The focus is on hardware interrupts, not software interrupt instructions.

We are dealing specifically with the Intel 8085 microprocessor.

Each hardware interrupt is associated with a physical input pin on the chip.

Software interrupts such as RST instructions are not being counted here.

We need to count distinct external interrupt input lines.

Concept / Approach:
The Intel 8085 provides five hardware interrupt input lines: TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. TRAP is a non maskable and highest priority interrupt, while the three RST interrupts are maskable and vectored. INTR is a general purpose, non vectored maskable interrupt input. Together these five lines form the hardware interrupt system of the 8085. In addition to these, the 8085 supports eight software interrupts through RST instructions from RST 0 to RST 7, but those are generated by program instructions and are not physical input pins.

Step-by-Step Solution:
Step 1: List the hardware interrupt lines of the 8085: TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR.Step 2: Count these distinct inputs to get the total number of hardware interrupts.Step 3: Observe that this count is equal to five.Step 4: Compare this number with the options provided.Step 5: Select the option that states 5 hardware interrupts as the correct answer.

Verification / Alternative check:
Many standard microprocessor textbooks present a table or diagram listing the interrupt pins of the 8085. These resources consistently show TRAP at the top of the priority chain, followed by RST 7.5, RST 6.5, RST 5.5, and finally INTR. No other dedicated external interrupt inputs are provided on the chip. You can verify this by looking at the 8085 pin diagram which clearly labels these five pins, confirming that there are exactly five hardware interrupt lines.

Why Other Options Are Wrong:
The options 3 and 4 hardware interrupts are too low and would ignore one or more valid interrupt lines. The option 6 hardware interrupts suggests that there is an extra hardware interrupt which does not exist in the standard 8085. The option 8 hardware interrupts is often confused with the eight software interrupts RST 0 to RST 7, but those are not hardware pins. Therefore, all options other than five are incorrect for this question.

Common Pitfalls:
A frequent mistake is to mix up hardware and software interrupts and conclude that there are eight interrupts because of the RST instructions. Another pitfall is to forget that INTR is also a hardware interrupt and must be counted along with TRAP and the three RST interrupts. To avoid confusion, remember the list TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR, and note that this list contains exactly five entries.

Final Answer:
The Intel 8085 microprocessor provides 5 hardware interrupt input lines for external interrupt requests.