Microprocessor IO Interfacing Lecture Notes

Introduction to IO Interfacing

• Last topic in microprocessor philosophy: IO Interpretation.
• Two types of IO interfacing:
  • Isolated IO (IO Mapped IO)
  • Memory Mapped IO

Isolated IO (IO Mapped IO)

• Microprocessor directly connects to IO through an IO channel.
• Address Space:
  • Memory address space differs from IO address space.
• Signals:
  • Microprocessor uses signals to differentiate between memory and IO operations.
  • IO Read and IO Write signals are used.
  • Memory/IO bar: Used to select either memory or IO device.
• When signal is zero, IO devices are selected.
• When signal is one, memory is selected.

Memory Mapped IO

• Involves using memory to interface with IO devices.
• Memory and IO devices are interconnected.
• No direct use of IN and OUT instructions.
• Memory locations reserved for IO data exchange.
• Microprocessor uses memory read/write operations instead of direct IO operations.

Differences between Isolated IO and Memory Mapped IO

• Isolated IO: Direct connection, uses IN and OUT instructions.
• Memory Mapped IO: Uses memory as a medium, no IN and OUT instructions needed.

Instructions for IO Operations

IN Instruction

• Syntax: IN accumulator, port
• Purpose: Reads data from IO port into the accumulator.
• Port address can be 8 or 16 bit.

OUT Instruction

• Syntax: OUT port, accumulator
• Purpose: Writes data from accumulator to the IO port.

Even and Odd Addressing in IO

• Purpose: Allows handling of 16-bit data using 8-bit IO devices.
• Even Address: Used for lower byte.
• Odd Address: Used for higher byte.

Practical Examples

• Switch: Determines input as 0 or 1.
• LED: Controlled by writing 0 (OFF) or 1 (ON) to data line.

Programming Considerations

• Use of 8255 Programmable Peripheral Interface for connections.
• Port Addressing: Important for defining connections in programs.
• Address Decoder: Used to locate specific IO device or memory.

IO Interfacing Summary

• Two methods: Isolated and Memory Mapped.
• Important to understand signal usage and memory reservation for effective interfacing.

Please review these notes to ensure understanding of microprocessor IO interfacing concepts covered in the lecture.