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Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Introduction to 8255 and its Connection
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Today, we're going to discuss how to interface the 8255 Programmable Peripheral Interface with the 8085 microprocessor. Can anyone tell me why interfacing is important?
It's important to connect the CPU with peripheral devices for data transfer.
Exactly! The 8255 provides multiple I/O pins for communication. Now, what are the main components we need to connect?
The data lines, control lines, and address lines.
Correct! The data lines D0-D7 connect to the 8085's AD0-AD7. What are the significance of the control signals like RD and WR?
They manage the reading and writing of data.
Exactly! These control signals ensure we correctly manage data flow. Remember, the control signals change the state of communication. Let's summarize the main points: the importance of data transferring through connections, the role of control signals, and the necessity of address lines.
Understanding Address Decoding
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Now let's talk about address decoding. Why is it necessary for the 8255?
So we can communicate with the specific ports or control register of the 8255.
Brilliant! If we want to connect 8255 to a base address of 80H, what would our addresses for Port A, B, C, and Control Word Register be?
Port A would be 80H, B would be 81H, C would be 82H, and the Control Word would be 83H.
Excellent! Remember, when creating a Chip Select signal, we must consider higher order lines. What happens when these conditions are met?
The CS signal becomes active.
Exactly! Logical design using gates is critical in ensuring proper interfacing. Make sure you visualize this setup as it will help in practical understanding.
Programming and Understanding Functionality
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Now that we connected the 8255, how do we program it?
We need to send a control word to set the mode and directions of the ports.
Correct! How do we form the control word for a specific configuration?
We can use the format D7 D6 D5 D4 D3 D2 D1 D0 to indicate modes and directions.
Precisely! Let's say we want Port A as output, Port B as input. What would the bits look like?
It would be 1 for I/O mode, 00 for Group A Mode 0, 0 for output, and so on.
Right! After setting the control word, we can proceed to write data or read inputs based on this configuration. Great discussion on control word generation!
Practical Application and Troubleshooting
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We have talked about the interfacing and programming of the 8255. Now let's observe how this works in practice. What do we expect to see when we execute our programmed control word?
The LEDs connected to Port A should display states according to our output data.
Exactly! What about observing input from switches connected to Port B?
We should be able to read and reflect the states on Port C.
Great! Always remember to verify the connections and the control word before running the program. What could happen if we skip verification?
The outputs may not behave as expected.
Correct! Always troubleshooting is part of the process. Summarizing the practical aspects improves your programming and interfacing skills.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The section explains how to effectively connect and configure the 8255 PPI with the 8085 microprocessor. It delves into the control signals, data lines, and address decoding methods necessary for successful communication. Additionally, it outlines practical programming examples to manage outputs and inputs via the 8255.
Detailed
Interfacing 8255 with 8085
This section provides a comprehensive overview of how to interface the 8255 Programmable Peripheral Interface (PPI) with the 8085 microprocessor. The 8255 is designed to facilitate communication between the CPU and various peripheral devices through parallel data transfer. The intricacies of connectivity, including data lines, control signals, and address lines, are vital for smooth operation.
Key Points Covered:
- Data Lines:
- The D0-D7 data lines of the 8255 are directly connected to the multiplexed address/data lines AD0-AD7 of the 8085, allowing bidirectional data communication.
- Control Signals:
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The control signals are crucial for reading from and writing to the 8255. Here's how they connect:
- RD (Read): Connected to 8085 RD.
- WR (Write): Connected to 8085 WR.
- RESET: Connected to the 8085's RESET OUT.
- Address Lines and Chip Select:
- The Chip Select (CS) pin must be activated for communication, which is achieved through specific address decoding logic from the higher-order lines (A2-A15) of the 8085.
- Address lines A0 and A1 of the 8255 are directly linked to de-multiplexed outputs from the 8085, indicating which port (Port A, B, C) or the Control Word Register is being accessed.
- Address Decoding Logic:
- Employing simple logic gates, such as a NAND gate or 74LS138 Decoder, is suggested to create an active-low CS signal based on the selected I/O address range (e.g., 80H-83H).
- Example Setup:
- A simplified interfacing diagram illustrates how different lines connect between the 8255 and the 8085, ensuring a clear understanding of their operational interactions.
This section prepares the reader for practical applications involving programming the 8255 PPI, critical for input/output operations utilizing the 8085 microprocessor.
Audio Book
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Connecting Data Lines
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Connecting the 8255 to the 8085 involves connecting data lines, control lines, and address lines, along with address decoding logic.
- Data Lines: The D0-D7 pins of 8255 are connected directly to the AD0-AD7 (multiplexed data lines) of 8085.
Detailed Explanation
In this section, we are describing how to connect the 8255 PPI to the 8085 microprocessor using data lines. The 8255 has data pins labeled D0 to D7, which are used to transfer data between the 8255 and the microprocessor. These pins are connected to the first 8 lines of the 8085’s data bus, which are AD0 to AD7. When you send or receive data, it travels seamlessly through these connected lines.
Examples & Analogies
Think of the data lines like a road where cars (data) travel between two cities (the 8085 and 8255). The wider the road (more lines), the more cars can travel at the same time. In this case, having 8 lanes (D0-D7) allows for 8 bits of data to be sent simultaneously.
Control Line Connections
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- Control Lines:
- 8255.RD is connected to 8085.RD.
- 8255.WR is connected to 8085.WR.
- 8255.RESET is connected to 8085.RESET OUT.
Detailed Explanation
This chunk explains how to connect the control lines of the 8255 to the corresponding control lines of the 8085. The RD (Read) and WR (Write) signals are critical because they tell the 8255 when the CPU wants to read from or write to it. The RESET line is connected to initialize the 8255, ensuring all registers are cleared and reset to their default state.
Examples & Analogies
Imagine a traffic light system as the control lines. The RD and WR lines act like green lights telling cars when to go (read from or write to the 8255), while the RESET line is akin to a manual reset button that stops all traffic and sends cars back to the start.
Address Lines and Chip Select Activation
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- Address Lines and Chip Select (CS):
- 8255.A0 is connected to 8085.A0 (from the de-multiplexed address bus).
- 8255.A1 is connected to 8085.A1 (from the de-multiplexed address bus).
- The CS (Chip Select) pin of the 8255 needs to be activated (brought low) when the 8085 wants to communicate with the 8255. This is achieved using address decoding logic.
Detailed Explanation
In this chunk, we address the need for connect the address lines and the Chip Select of the 8255. The A0 and A1 pins from the chip define which specific register of the 8255 is being accessed. The CS pin allows the 8085 to enable the 8255 for communication. This means that without activating CS by applying the correct address signals, the 8255 will not respond even if data is sent through the data lines.
Examples & Analogies
Think of the address lines as the address numbers on your house street. When someone (the 8085) wants to visit, they need to know the exact address (the correct pin combinations) to knock on the right door (select the 8255’s specific register). Without knowing this address, they can’t get a response, similar to how the CS must be activated.
Example of Simple Address Decoding
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Example of Simple Address Decoding:
Let's assume we want to place the 8255's I/O ports at addresses 80H-83H.
- This means, for addresses 80H, 81H, 82H, 83H:
- A7 A6 A5 A4 A3 A2 A1 A0
- 1 0 0 0 0 0 A1 A0.
Detailed Explanation
In this chunk, we demonstrate how to perform address decoding. By assigning the 8255 to specific addresses (80H to 83H), we can uniquely identify its ports. Here we use the higher address lines (A7-A5) to define the range and the lower address lines (A1 and A0) to select the specific ports (Port A, Port B, Port C, and Control Word Register). This is crucial for ensuring the 8085 accesses the correct device when it sends or receives data.
Examples & Analogies
Address decoding is like having a library with several sections. Each section has a unique label (address range), and knowing which label to look for helps you go directly to the right section (I/O port) to find the right book (data) quickly.
Simplified Interfacing Diagram Concept
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Simplified Interfacing Diagram Concept:
8085 Microprocessor | 8255 PPI
AD0-AD7 (Data Bus) -----------------|---------- D0-D7 (Data Bus)
RD (Read) --------------------------|---------- RD
WR (Write) -------------------------|---------- WR
RESET OUT --------------------------|---------- RESET
A0 (De-multiplexed)-----------------|---------- A0
A1 (De-multiplexed)-----------------|---------- A1
A2-A15 (Address lines) ----> Address Decoding Logic --> CS (Chip Select)
IO/M (Control Signal) ----^
Detailed Explanation
This portion provides a conceptual diagram to visually represent the interfacing process between the 8085 and the 8255. It outlines how data flows between the two devices, illustrating connections clearly. Each signal line's purpose is defined, aiding in understanding the overall interaction during data transmission and reception.
Examples & Analogies
Visualizing the interfacing as a detailed map can help. Each line (connection) represents pathways on the map, showing where each destination leads. By following the right pathways (data and address lines), one can navigate easily from the microprocessor to the peripheral device.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Data Lines: Key lines used for transmitting data.
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Control Signals: Signals used for managing reads and writes.
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Address Decoding: Process that ensures correct device communication.
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Control Word: Configuration instructions sent to the 8255.
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Chip Select: Enables communication through signal management.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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Connecting the 8255 to the 8085 involves linking data lines D0-D7 to AD0-AD7.
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To activate the Chip Select, decode the addresses A0 and A1 appropriately.
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Sending a control word like 8AH sets Port A as output, Port B as input, etc.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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For ports to connect with the CPU, lines D0 to D7 must be true.
📖 Fascinating Stories
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Imagine a busy post office where the 8085 CPU is the manager, and the 8255 is the clerk sorting the data parcels (I/O data). They need clear labels (Control Word) to ensure the right parcels go to the right place.
🧠 Other Memory Gems
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Remember the acronym CODES: Control Word, Output for Port A, Data flow, Enable signals, Select signals.
🎯 Super Acronyms
PASC - Ports (A, B, C), Address Decoding, Signals (Control), Configuration (Control Word).
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: 8255 Programmable Peripheral Interface (PPI)
Definition:
A versatile device used to interface microprocessors with parallel I/O devices.
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Term: Control Word
Definition:
An 8-bit word sent to configure the operating modes of the 8255.
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Term: Chip Select (CS)
Definition:
A signal enabling communication with the 8255 by going low.
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Term: Data Lines
Definition:
Lines used to transmit data between the microprocessor and the 8255.
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Term: Address Decoding
Definition:
The process of deciding which device to communicate with based on the address provided.