I/O Instructions - 2.3.3 | Module 2: Microprocessor Architectures: 8085 and 8086 | Microcontroller
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2.3.3 - I/O Instructions

Practice

Interactive Audio Lesson

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Introduction to I/O Instructions

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0:00
Teacher
Teacher

Today, we're diving into I/O instructions of the 8085 microprocessor. Who can tell me what I/O stands for?

Student 1
Student 1

Input/Output?

Teacher
Teacher

Exactly! I/O refers to the way a microprocessor interacts with external devices. The 8085 supports unique port addresses for these operations. Can anyone guess how many unique I/O addresses it supports?

Student 2
Student 2

Is it 256, sir?

Teacher
Teacher

Correct! It supports addresses from 00H to FFH. Now, can anyone explain how we input data from an I/O port?

Student 3
Student 3

You use the IN instruction.

Teacher
Teacher

Right! The syntax is IN Port_Adr. For example, IN 05H reads data from port 05H into the accumulator. Let's remember: 'I in the accumulator'. What do you think the OUT instruction does?

Student 4
Student 4

It sends data to an I/O port.

Teacher
Teacher

Exactly! The syntax is OUT Port_Adr. Well done everyone! Let’s recap. We learned that I/O instructions help the 8085 interact with external devices through specific addresses using IN and OUT.

Examples of I/O Instructions

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0:00
Teacher
Teacher

Let’s discuss real examples. If I say 'IN 05H', what is happening in the microprocessor?

Student 1
Student 1

It reads 8 bits from port 05H into the accumulator.

Teacher
Teacher

Correct! Now, what about 'OUT 0AH'?

Student 2
Student 2

We send the accumulator content to port 0AH.

Teacher
Teacher

Exactly! Can someone tell me the importance of these instructions in a practical context?

Student 3
Student 3

They allow the microprocessor to interact with hardware like keyboards, displays, and sensors.

Teacher
Teacher

Well said! Such interactions are essential for computer applications. Remember, I/O instructions are the gateways for data transfer between the microprocessor and its environment.

Student 4
Student 4

So, without these instructions, the microprocessor wouldn’t communicate with external devices?

Teacher
Teacher

Absolutely! That’s the key takeaway for today. Let’s summarize: The IN instruction reads from a port to the accumulator, and the OUT instruction sends data from the accumulator to a port.

Introduction & Overview

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Quick Overview

The I/O instructions section covers how the 8085 microprocessor interacts with external devices through I/O ports, facilitating data transfer between the accumulator and I/O ports.

Standard

This section details the I/O instruction set of the 8085 microprocessor, including how to read data from an input port and output data to an output port. The section also describes the two types of I/O addressing: memory-mapped I/O and I/O-mapped I/O.

Detailed

I/O Instructions

The 8085 microprocessor uses special instructions to facilitate communication with external devices through I/O ports. This section highlights the key aspects of these I/O instructions, which are essential for enabling data transfer between the internal accumulator and I/O ports. The two types of I/O addressing are identified: memory-mapped I/O and I/O-mapped I/O. In the 8085 architecture, a total of 256 unique I/O port addresses are supported (from 00H to FFH).

Input from Port

  • IN Port_Adr: This instruction allows the microprocessor to read an 8-bit byte from a specified port address and store it in the accumulator. For example, IN 05H reads data from I/O port address 05H into the accumulator.

Output to Port

  • OUT Port_Adr: This instruction is used to send the contents of the accumulator to a specified 8-bit port address. For instance, OUT 0AH sends the data from the accumulator to I/O port address 0AH.

Understanding I/O instructions is critical for working with input and output devices, allowing for interaction with peripheral systems.

Audio Book

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Overview of I/O Instructions

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These instructions are used to transfer data between the Accumulator and an I/O port. The 8085 uses memory-mapped I/O or I/O-mapped I/O. It supports 256 unique I/O port addresses (from 00H to FFH).

Detailed Explanation

The I/O instructions of the 8085 microprocessor facilitate communication between the processor and peripheral devices (like keyboards, printers, etc.). Each device has an I/O port, which is like an address for the device. The 8085 can work with these devices using specific addresses from 00H to FFH. The term 'memory-mapped I/O' indicates that I/O devices are treated like memory locations, allowing the CPU to access them in a similar way by using read and write commands.

Examples & Analogies

Imagine your computer's USB ports as specific addresses for different devices like a mouse, keyboard, or printer. Just as you can use a different address to send data to each device, the 8085 can send data to a specified I/O port. For instance, when you click a key on the keyboard, the signal is sent via its dedicated address, similar to the I/O instructions used in the microprocessor.

Input from Port

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Input from Port:
- IN Port_Adr: Read an 8-bit byte from the specified 8-bit Port_Adr and store it in the Accumulator.

Numerical Example: IN 05H. Reads data from I/O port address 05H into Accumulator A.

Detailed Explanation

The IN instruction allows the processor to receive data from an I/O port. When the instruction 'IN Port_Adr' is executed, the 8085 reads an 8-bit byte from the specified port address and places that byte into the Accumulator, which is the main register for data storage during processing. This allows the CPU to use the data it receives for further operations.

Examples & Analogies

If you consider a vending machine, the input port might be likened to a button you press to get a snack. When you press the button (IN command), the machine retrieves the snack (data) and stores it in a designated area (the Accumulator) for your later enjoyment.

Output to Port

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Output to Port:
- OUT Port_Adr: Send the content of the Accumulator to the specified 8-bit Port_Adr.

Numerical Example: OUT 0AH. Sends data from Accumulator A to I/O port address 0AH.

Detailed Explanation

The OUT instruction enables the processor to send data out to an I/O port. When 'OUT Port_Adr' is executed, the CPU transfers the data currently in the Accumulator to the specified port address. This data could be anything from character outputs to control signals for devices like monitors or printers.

Examples & Analogies

Think of the OUT instruction as sending a letter to a friend. Just like putting a letter into a mailbox (the OUT command) to deliver a message to your friend's address (the port), the CPU sends data from the Accumulator to the specified I/O port for output operations.

Definitions & Key Concepts

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Key Concepts

  • I/O Port Addresses: The 8085 microprocessor supports 256 unique I/O port addresses ranging from 00H to FFH.

  • IN Instruction: Used to read data from an I/O port into the accumulator.

  • OUT Instruction: Used to write data from the accumulator to an I/O port.

Examples & Real-Life Applications

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Examples

  • Example 1: 'IN 05H' reads an 8-bit byte from I/O port 05H into the accumulator.

  • Example 2: 'OUT 0AH' sends the content of the accumulator to I/O port 0AH.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • IN to read, OUT to send, with these instructions, data will blend.

📖 Fascinating Stories

  • Imagine a postman, the IN is when he reads the letters arriving at the post office, while the OUT is when he sends them out to the addresses.

🧠 Other Memory Gems

  • I for Input (IN), O for Output (OUT) - just think 'IN goes in, OUT goes out'.

🎯 Super Acronyms

I.O. - Input/Output

  • Think of 'I/O' as your pathway for communication with devices.

Flash Cards

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Glossary of Terms

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  • Term: I/O Instructions

    Definition:

    Instructions that allow the microprocessor to transfer data between the accumulator and I/O ports.

  • Term: IN

    Definition:

    Instruction used to read an 8-bit byte from an I/O port to the accumulator.

  • Term: OUT

    Definition:

    Instruction used to send the content of the accumulator to an I/O port.

  • Term: I/O Port

    Definition:

    The specific address used to interface the microprocessor with external devices.

  • Term: Memorymapped I/O

    Definition:

    A method where I/O devices are treated as memory locations.

  • Term: I/Omapped I/O

    Definition:

    A method where I/O devices have specific, distinct addresses for communication.