In the 8085 microprocessor, when RD signal is low and IO/M signal is high, the instruction is in the _______ cycle of execution.

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Answer 1

Concept:

8085 Microprocessor Signals and Execution Cycles

The 8085 microprocessor uses various control and status signals to manage its operations and interactions with memory and I/O devices.
Among these signals, RD (Read) and IO/M (Input/Output/Memory) are crucial for determining the type of operation being performed.
The RD signal is active low, meaning that when it is low, the microprocessor is in a read operation.
The IO/M signal indicates whether the operation involves memory or an I/O device. When IO/M is high, it signifies an I/O operation; when it is low, it signifies a memory operation.

Explanation of the Correct Option:

When RD signal is low and IO/M signal is high, the microprocessor is performing an I/O read operation.
In this scenario, the microprocessor reads data from an input device. The low RD signal indicates that data is being read, and the high IO/M signal specifies that the read operation is targeting an I/O device rather than memory.
The combination of RD being low and IO/M being high unequivocally points to an I/O read cycle. During this cycle, the microprocessor places the address of the I/O device on the address bus and activates the RD signal to read data from the I/O port.
The I/O device responds by placing the data onto the data bus, which the microprocessor then reads and processes as required.

Conclusion:

In the 8085 microprocessor, when RD signal is low and IO/M signal is high, the instruction is in the I/O read cycle of execution. Hence, it is the correct option.

Important Information Analysis of Other Options:

I/O write: This operation occurs when the microprocessor writes data to an output device. It is indicated by WR (Write) signal being low and IO/M signal being high. In this case, the combination of signals (RD low and IO/M high) does not match, so this option is incorrect.
Memory write: This operation involves writing data to a memory location. It is indicated by WR (Write) signal being low and IO/M signal being low. Again, the given signals (RD low and IO/M high) do not correspond to a memory write operation, making this option incorrect.
Memory read: This operation involves reading data from a memory location. It is indicated by RD (Read) signal being low and IO/M signal being low. The given signals (RD low and IO/M high) do not indicate a memory read operation, making this option incorrect.