GATE CS 2001 Q1.9 — Machine Instructions and Addressing Modes

The correct option is D.

The READY pin on the 8085 microprocessor is used to interface slow memory or slow I/O devices with the fast microprocessor:

• Function of READY: When a slow memory device is accessed, it cannot respond within the standard machine cycle of the microprocessor. To prevent data loss, the memory device pulls the READY pin of the 8085 to low (logic 0).
• Wait States: On sensing a low signal on the READY pin, the 8085 microprocessor enters into one or more WAIT states, suspending its operation and holding the address and control signals constant.
• Synchronization: Once the memory device completes its read/write preparation, it drives the READY pin high (logic 1). The microprocessor then exits the wait state and completes the data transfer.

Why other options are incorrect:

• $INTR$ (Interrupt Request): Used by external devices to initiate an interrupt service routine.
• $\overline{RESET\text{ }IN}$: Used to reset the microprocessor (sets PC to 0000H).
• $HOLD$: Used by external devices (like DMA controllers) to request control of the address and data buses.