Program 1: 8255 Initialization and Static Output to Port A - 4.1 | EXPERIMENT NO. 3 TITLE: Parallel I/O Interfacing with 8085 (8255 Programmable Peripheral Interface) | Microcontroller Lab
K12 Students

Academics

AI-Powered learning for Grades 8–12, aligned with major Indian and international curricula.

Professionals

Professional Courses

Industry-relevant training in Business, Technology, and Design to help professionals and graduates upskill for real-world careers.

Games

Interactive Games

Fun, engaging games to boost memory, math fluency, typing speed, and English skills—perfect for learners of all ages.

Typing
Memory
Math
English Adventures
Knowledge

4.1 - Program 1: 8255 Initialization and Static Output to Port A

Practice

Interactive Audio Lesson

Listen to a student-teacher conversation explaining the topic in a relatable way.

Introduction to 8255 Initialization

Unlock Audio Lesson

Signup and Enroll to the course for listening the Audio Lesson

0:00
Teacher
Teacher

Today, we are starting with the initialization of the 8255 PPI. Can anyone tell me why it's important to set up our peripheral interface before we use it?

Student 1
Student 1

If we don't configure it, the data might not flow correctly between the CPU and the peripheral.

Teacher
Teacher

Exactly! If not configured properly, you may experience erratic behavior. The first step is to determine our Control Word. Can anyone explain what a Control Word is?

Student 2
Student 2

It's the instruction we send to the 8255 to tell it how to operate.

Teacher
Teacher

Right! It sets up the configuration for all the ports. Now, let’s touch on what modes we can use with 8255. Who can recall the modes available?

Student 3
Student 3

There are Mode 0, Mode 1, and Mode 2. Mode 0 is for basic I/O without handshaking.

Teacher
Teacher

Yes, Mode 0 is what we will focus on. Let's summarize the control word format that we will calculate next.

Control Word Calculation

Unlock Audio Lesson

Signup and Enroll to the course for listening the Audio Lesson

0:00
Teacher
Teacher

Now we need to calculate our Control Word for configuring Port A as an output. Let's break down the bits needed for our configuration.

Student 4
Student 4

The structure is 8 bits, right? What do each of those bits represent?

Teacher
Teacher

Good question! The first bit, D7, indicates the mode—set to '1' for I/O mode. Can you help determine what the Control Word looks like with our setup?

Student 1
Student 1

D6 and D5 for Group A Mode would be '00' for Mode 0, D4 should be '0' for output on Port A, and so on.

Teacher
Teacher

Exactly! After working through it, we would have: 10001010 in binary or 8AH in hexadecimal. Now, let's prepare the assembly instructions.

Writing Assembly Code

Unlock Audio Lesson

Signup and Enroll to the course for listening the Audio Lesson

0:00
Teacher
Teacher

Next, we will write the assembly code to initialize the 8255 and send the data byte to Port A. Let’s review the purpose of each line.

Student 2
Student 2

The first line is to load the control word into the accumulator, then we use OUT to send it.

Student 3
Student 3

What about when we send the data byte? What's the logic behind that?

Teacher
Teacher

Great observation! After configuring the ports, we send a static byte. In our case, it will illuminate certain LEDs connected to Port A.

Student 4
Student 4

And what will the expected outcome be for the LEDs?

Teacher
Teacher

If everything is set correctly, you should see the pattern corresponding to the data byte we sent, which is 55H or 01010101 binary.

Expected Outcomes and Observations

Unlock Audio Lesson

Signup and Enroll to the course for listening the Audio Lesson

0:00
Teacher
Teacher

Lastly, let's circle back to the outcomes of our program execution. What should we observe after running the code?

Student 1
Student 1

We should see LEDs turning ON and OFF according to the data we sent.

Student 2
Student 2

And the accumulator value should be 55H after the output operation, right?

Teacher
Teacher

Correct! Also, you can monitor the program counter to ensure it advances as expected. Always remember to verify and confirm your results.

Student 3
Student 3

So, testing feedback is crucial to determine if our setup is working properly?

Teacher
Teacher

Absolutely! Never skip the observation step as it is part of learning.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section covers the initialization of the 8255 Programmable Peripheral Interface to configure its ports and output a static value to Port A.

Standard

The section outlines the objective of configuring the 8255 in Mode 0, setting up Port A as an output port, and sending a fixed data byte to control LEDs. It provides detailed control word calculations, assembly code, and expected outcomes.

Detailed

8255 Initialization and Static Output to Port A

This section is crucial as it illustrates how to initialize the 8255 Programmable Peripheral Interface (PPI) and set it up for specific operations. The objective is to configure the 8255 for Mode 0, where Port A is set as an output port to control connected LEDs, while Port B acts as an input and Port C lower serves as an output port. To achieve this, a Control Word is calculated based on required directions for ports. The Control Word, in this case, determines the operating modes and data flow for the ports. After calculating the Control Word, students will implement assembly code to output a fixed data byte to Port A that illuminates the LEDs.

Key Points Covered:

  • The importance of configuring the PPI correctly before use.
  • Methods to calculate the appropriate Control Word for desired configurations.
  • Step-by-step assembly code to perform the initialization and to send data to Port A.
  • Expected outcomes, including visual feedback from connected LEDs.

This process enhances understanding of interfacing microprocessors with peripherals and lays groundwork for future experiments involving the 8255.

Audio Book

Dive deep into the subject with an immersive audiobook experience.

Objective of Program 1

Unlock Audio Book

Signup and Enroll to the course for listening the Audio Book

Objective: To configure 8255 for Mode 0 (Port A as Output, Port B as Input, Port C Lower as Output, Port C Upper as Input) and then output a fixed data byte (55H) to Port A.

Detailed Explanation

The objective of this program is to set up the 8255 circuit so that different ports operate in specific ways. For instance, Port A is configured to send data out (output), while Port B is set up to receive inputs (input). Additionally, part of Port C will also be used to send outputs. The fixed data byte, 55H (which in binary is 01010101), will be sent to Port A, which could control the state of various connected LEDs.

Examples & Analogies

Think of it like setting up a remote control for a toy. You want a specific button (Port A) to make the toy move forward (output) and another button (Port B) to receive signals from the wall to stop (input). The fixed data byte 55H would be akin to sending a specific code that indicates the toy’s direction.

Control Word Calculation

Unlock Audio Book

Signup and Enroll to the course for listening the Audio Book

Control Word Calculation (I/O Mode):
- D7 = 1 (I/O Mode)
- D6, D5 (Group A Mode) = 00 (Mode 0)
- D4 (Port A Direction) = 0 (Output)
- D3 (Port C Upper Direction) = 1 (Input)
- D2 (Group B Mode) = 0 (Mode 0)
- D1 (Port B Direction) = 1 (Input)
- D0 (Port C Lower Direction) = 0 (Output)
- Resulting Control Word (Binary): 10001010b = 8AH (Hex).

Detailed Explanation

To configure the 8255 correctly, a control word is sent, which is an 8-bit value that specifies the operational mode and the direction of each port. Each bit in the control word corresponds to different aspects of the configuration: enabling input/output modes for the ports and specifying whether they should be configured for inputs (to read) or outputs (to write data). The resulting control word in binary is 10001010, which can be translated to hexadecimal format as 8AH.

Examples & Analogies

Imagine setting the settings on your gaming console. Each setting (like volume, brightness, or language) has a specific switch position (ON or OFF). The control word is like a master switch that tells the console what configurations to use so that you can enjoy your gaming experience.

Assembly Code for Initialization

Unlock Audio Book

Signup and Enroll to the course for listening the Audio Book

Assembly Code:

; Program to initialize 8255 and output static data to Port A
; Starting Address: 2000H
ORG 2000H
MVI A, 8AH ; Load Accumulator with 8255 Control Word for desired configuration
OUT 83H ; Write Control Word to 8255 CWR (Port A=Out, B=In, C_L=Out, C_U=In)
MVI A, 55H ; Load Accumulator with data to be sent to Port A
OUT 80H ; Output data (55H) to Port A (connected to LEDs)
HLT ; Halt processor execution

Detailed Explanation

The assembly code begins with defining a starting address. Then, the process involves loading the control word into the accumulator, which is a temporary storage where data can be manipulated before being sent out to the hardware. The next line writes this control word to the 8255's control register, effectively configuring the device. After setting up, the code loads a fixed data byte (55H) into the accumulator and outputs it to Port A, which might be connected to LEDs, making those LEDs display a specific pattern.

Examples & Analogies

Consider this assembly code as a step-by-step recipe. Just like how you need to prepare ingredients (loading the control word) before cooking (outputting data to Port A), each step builds up to the final dish, which in this case results in the LEDs functioning as intended.

Memory Layout of the Program

Unlock Audio Book

Signup and Enroll to the course for listening the Audio Book

Memory Layout (Hex Code):
| Address | Hex Code | Instruction | Comments |
| :------ | :------- | :------------------ | :------------------------ |
| 2000H | 3E | MVI A, 8AH | |
| 2001H | 8A | | |
| 2002H | D3 | OUT 83H | |
| 2003H | 83 | | |
| 2004H | 3E | MVI A, 55H | |
| 2005H | 55 | | |
| 2006H | D3 | OUT 80H | |
| 2007H | 80 | | |
| 2008H | 76 | HLT | |

Detailed Explanation

The memory layout details how the program is stored in memory. Each address contains a specific instruction or data needed for execution. Each instruction has associated hex codes that the microprocessor understands. This mapping is critical because it instructs the microprocessor where to find each part of the program during execution.

Examples & Analogies

Think of this layout like a library shelf. Each address is a different book (instruction) that has to be read in order to learn how to assemble your final project (the functioning 8255). If the information (instruction) is in the wrong spot, you won't be able to build it correctly.

Expected Outcomes

Unlock Audio Book

Signup and Enroll to the course for listening the Audio Book

Expected Outcomes:
- Port A LEDs should display the binary pattern for 55H (01010101b).
- Registers: A = 55H, PC = 2009H.

Detailed Explanation

Upon running the program, the expected output is that the LEDs connected to Port A will light up in a pattern that corresponds to the binary representation of the number 55 (01010101). Each bit in this number represents an LED, where '1' indicates the LED is on, and '0' indicates it is off. Additionally, certain registers in the microprocessor will contain the values that confirm the operations performed.

Examples & Analogies

If you were to program a sequence of lights at a concert, you would expect them to light up in a specific sequence based on the signals you send. Watching the lights react according to your specified pattern reflects how the expected outcomes work in this program.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Initialization of 8255: It's crucial for proper operation.

  • Control Word Format: Specifies operational modes for ports.

  • Mode 0 Operation: Basic I/O without handshaking.

  • Data Flow: Involves loading data into the accumulator and outputting it.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • To send the value 55H to Port A, we first load the accumulator with 55H and then use OUT 80H to send the data.

  • The calculated Control Word for setting Port A as output while keeping Port B as input is 8AH.

Memory Aids

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

🎵 Rhymes Time

  • For Control Word, don’t be shy, set your bits, let data fly!

📖 Fascinating Stories

  • Imagine the 8255 as a bus station: each port represents a different bus. The Control Word functions as a bus schedule detailing where each bus goes and how it operates.

🧠 Other Memory Gems

  • Remember 'C.A.P.E': Control Word - Address Ports - Execute, to recall the steps of sending data.

🎯 Super Acronyms

Use the acronym 'P.I.O'

  • Port Initialize Output to remember how to configure and utilize ports.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Control Word

    Definition:

    An instruction sent to the 8255 to configure its operational mode and port directions.

  • Term: Mode 0

    Definition:

    The basic input/output mode for the 8255, allowing ports to function without handshaking.

  • Term: Accumulator

    Definition:

    A register in the CPU that receives data from operations and outputs results.

  • Term: LED

    Definition:

    Light Emitting Diode, used here as output devices connected to the 8255 for visual feedback.

  • Term: Port A

    Definition:

    One of the three ports of the 8255, can be configured as input or output.