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Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Initial Setup and System Powering
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Alright students, today we are going to learn about interfacing the 8255 PPI with the 8085 microprocessor. The first step is to power on the trainer kit. Can anyone tell me why it's important to reset the system before starting?
I think we reset it to ensure all registers are cleared and initialized to a known state.
Exactly! This helps avoid unexpected behavior. Now, what addresses do we need to identify for Port A, Port B, Port C, and the Control Word Register?
They are usually provided in the trainer kit manual, right?
That's right! Knowing the addresses is crucial for our next steps. Remember, for our kit, let's assume the addresses are 80H for Port A, 81H for Port B, 82H for Port C, and 83H for the Control Word Register. Let's not forget to connect the LEDs correctly! Can anyone explain why current limiting resistors are necessary when connecting LEDs?
We need them to prevent excessive current which can burn out the LEDs.
Excellent point! Proper setup ensures our circuit operates safely and effectively.
Control Word Calculation
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Now that we have our setup ready, let's discuss the control word we need to write to the 8255. Does anyone remember the bits we need for configuring the 8255?
Yes! We need D7 for mode selection, and the other bits to set directions for Ports A, B, and C.
Very good! Can anyone tell me how D7 functions depending on whether we are in I/O mode or BSR mode?
D7 is set to 1 for I/O mode and 0 for BSR mode.
Great! Let’s take an example where we configure Port A as output, Port B as input, and the lower half of Port C as output. Can someone help formulate that control word?
If Port A is output, that means D4 is 0, and since Port B is input, D1 is 1. The control word should result in a certain hexadecimal value, right?
Exactly. And we’ve seen it can be quite fun to calculate this control word based on our configurations!
Entering and Executing Programs
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Next, we need to enter assembly language programs into our system. Who can describe how we might confirm that they were entered correctly?
We can use a command like EXAM MEM to check the memory addresses.
Well said! It’s important we ensure accuracy before execution. What command would we use to run our program once entered?
We use the GO command followed by the start address!
Perfect! Now, once we execute, what should we observe on the LEDs or switches?
We should see the actual output based on the program we wrote; for example, the LEDs should turn ON or OFF as programmed.
That's right! Observing these outputs is part of the hands-on learning experience.
Input and Output Observation
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Now let's shift our focus to input observations. When we read switches, how can we verify that the data is accurate?
We can check the accumulator’s content after the IN instruction to see if it matches the switch states.
Exactly! And what happens if we see unexpected results?
We might need to double-check our connections and control word settings.
Exactly! Troubleshooting is a critical part of working with hardware. Why do you think it's essential to keep track of LED statuses as we execute programs?
To confirm that the output directly correlates to our input data.
Exactly, understanding this relationship is core to mastering I/O interfacing!
Review and Conclusion
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As we conclude, let's summarize what we have learned today regarding interfacing the 8255. Can anyone recall why the control word is essential?
It configures the modes and directions of the ports before we can interact with them.
Exactly! This configuration allows us to utilize the device effectively for both outputs and inputs. What about the significance of observing LED states?
It helps us confirm whether the program is functioning as intended—the real-time feedback is crucial!
Perfectly summed up! The practical understanding gained through this procedure solidifies our grasp of interfacing concepts.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The procedure illustrates the steps needed to set up the 8085 trainer kit for parallel I/O interfacing using the 8255 PPI. It includes system initialization, programming, and observing outputs on connected devices like LEDs and switches through detailed assembly programming.
Detailed
Procedure Overview
This section presents the comprehensive procedure for interfacing the 8255 Programmable Peripheral Interface (PPI) with the 8085 microprocessor. The procedure is divided into several key phases, including system setup, initialization, and program execution.
1. System Setup and 8255 Initialization
You will begin by powering on your 8085 trainer kit. It’s essential to identify the I/O addresses allocated to Port A, Port B, Port C, and the Control Word Register. Proper connections must be made to external LEDs or switches if they are not already integrated with the trainer kit. The control word for the 8255 is calculated based on the desired configuration for input and output operations.
2. Program Entry and Execution
Assembly programs are entered into specific memory locations on the trainer kit. The execution of these programs is done through commands like ‘GO’ or ‘EXEC’ to verify real-time changes in output and to observe how the system reads data from input ports.
3. Observation
During execution, students are expected to observe the behavior of connected LEDs or read inputs from switches. Verifying the read status by examining register contents is crucial to the learning process.
This procedure provides hands-on experience with parallel I/O operations and illuminates how to control peripherals using assembly language in conjunction with the 8085 and 8255 architecture.
Audio Book
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Observation
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- Observe Output LEDs: For programs configuring ports as output, visually observe the state of the connected LEDs (ON/OFF) as the program executes.
- Observe Input Switches: For programs configuring ports as input, change the state of the connected switches and then read the corresponding input port using the program. Verify the read data on the display or by checking register contents.
- Examine Registers/Memory: Use the trainer kit's commands (EXAM REG, EXAM MEM) to verify the contents of the Accumulator and other registers, especially after IN instructions to confirm input data was correctly read.
Detailed Explanation
In this section, students are guided on how to verify the results of their assembly programs. The first point emphasizes monitoring the output LEDs, which serve as a direct visual representation of the program's functionality. If the port has been configured correctly, changing the program should directly affect the LEDs' states (on or off). Next, students are instructed to interact with the input switches; by manipulating these switches, they should observe corresponding changes in the registers or memory as the program reads these inputs. Lastly, examining the values stored in registers is crucial for debugging and understanding what data has been processed after executing input instructions. This step provides insight into how well the hardware interaction is functioning and allows students to validate the logic behind their programming in real-time.
Examples & Analogies
This observation phase is much like a science experiment where you finally get to see the results of your hard work. Imagine you've followed a series of steps to grow a plant, and now you're observing how tall it has grown or how many flowers it has produced—these LEDs and switch states are the 'results' of your programming experiment. Each change you make regarding the soil, water, or sunlight can be observed as the plant continues to grow, similar to testing different inputs and outputs with the hardware to see the direct effects.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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System Reset: Powering on and resetting the trainer kit is fundamental to clear all registers.
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Control Word Calculation: Understanding how to formulate the control word for configuring the 8255 is essential for correct operation.
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Input/Output Operations: The procedure outlines how to connect devices, enter programs, execute, and verify outputs effectively.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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Example of Control Word: If Port A is output and Port B is input, the control word would be calculated to reflect these configurations.
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Example of LED observation: After writing to Port A, if the LEDs should display the binary pattern set in previous instructions, observing their status validates the program's success.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Control word in hand, ports under command.
📖 Fascinating Stories
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Imagine a classroom where 8255 is a teacher, directing ports like students based on a control word that sets the rules!
🧠 Other Memory Gems
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C-P-P for Control (C), Port A (P), Port B (P) settings.
🎯 Super Acronyms
I/O for Input/Output; Remember to set up before you go!
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: PPI
Definition:
Programmable Peripheral Interface, a device that allows microprocessors to interface with peripheral devices.
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Term: Control Word
Definition:
An 8-bit word used to configure the operational modes and directions of the 8255 ports.
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Term: Port
Definition:
A set of pins on the 8255 used for input or output of signals.
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Term: Mode 0
Definition:
Basic I/O mode where data can be read or written directly to the ports without requiring handshaking.
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Term: IN Instruction
Definition:
An instruction used to read data from an input port.
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Term: OUT Instruction
Definition:
An instruction used to send data to an output port.