Microprocessor Interrupt Acknowledgement with INTR

When an external device needs to signal the microprocessor about an event that requires immediate attention, it typically sends an interrupt request (INTR) signal. The microprocessor must then acknowledge this request appropriately. The question specifically asks about the signal used to supply an address instruction during this acknowledgement phase.

INTA Signal: Providing Address Instructions

The microprocessor uses specific control signals to manage interrupts. For the INTR signal, the acknowledgement process involves the INTA (Interrupt Acknowledge) signal.

• Upon receiving an INTR signal, the microprocessor, if enabled for interrupts, will eventually respond by asserting the INTA signal.
• The external device that requested the interrupt monitors for this INTA signal.
• When the interrupting device detects the INTA signal, it places an interrupt vector or a specific address instruction onto the data bus.
• This address instruction is crucial as it helps the microprocessor identify the interrupting device or the specific interrupt service routine (ISR) to execute.

Distinguishing Processor Signals: INTA, HOLD, HLDA

It's important to understand the roles of different processor signals to see why INTA is the correct choice:

• INTA (Interrupt Acknowledge): Directly involved in acknowledging the INTR signal and fetching the interrupt vector/address instruction.
• HOLD: This signal is used by external devices to request control of the system bus, often for Direct Memory Access (DMA). It's related to bus arbitration, not interrupt handling.
• HLDA (Hold Acknowledge): This is the microprocessor's response to a HOLD request, indicating it has relinquished control of the bus. It does not relate to interrupt acknowledgement.

Processor CALL Instruction vs. INTA Signal

The CALL option is also different:

• CALL: This is an internal microprocessor instruction. It's used to transfer program control to a subroutine (a block of code that performs a specific task). It is not an external signal used for acknowledging interrupts.

Conclusion on INTR Acknowledgement

Based on the functions of these signals, the INTA signal is the one used by the microprocessor to acknowledge the INTR signal, and during this acknowledgement, the external device supplies the required address instruction.