Solusi 8255 Programmable Peripheral Interface With 8086

𝕸𝖆𝖘 𝕬𝖓𝖉𝖞 𝕯𝖎𝖌𝖎𝖙𝖆𝖑 𝕸𝖊𝖉𝖎𝖆

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Mar 20, 2025

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The Complete Recipe: Interfacing 8255 Programmable Peripheral Interface with 8086

The 8255 Programmable Peripheral Interface (PPI) is a versatile and widely used device for interfacing peripherals with the 8086 microprocessor. Understanding how to interface these two components is crucial for anyone working with embedded systems or microcomputer architecture. This article provides a complete recipe, detailing the steps and considerations required for successful interfacing.

Understanding the Ingredients: 8086 and 8255

Before we dive into the recipe, let's understand the key players:

• 8086 Microprocessor: This is the central processing unit (CPU), responsible for executing instructions and managing data flow. Its architecture, including its memory addressing and bus structures, is crucial to understanding the interface process.

• 8255 Programmable Peripheral Interface: This is a programmable parallel I/O device. Its flexibility stems from its ability to configure its three 8-bit ports (A, B, and C) in various modes, allowing for diverse input/output operations like simple I/O, strobed I/O, and bidirectional I/O. Understanding these modes is key to choosing the right configuration for your specific peripheral.

The Recipe: Interfacing 8255 with 8086

This recipe outlines the steps needed to interface the 8255 with the 8086, encompassing hardware connection and software programming.

1. Hardware Connection:

• Address Decoding: The 8255 needs a unique memory address to be accessed by the 8086. This is achieved using address decoding circuitry, often involving logic gates like AND, OR, and NOT gates. This process ensures only the 8255 responds to the specific memory address assigned to it. Careful selection of address lines and chip select (CS) signals is crucial.

• Data Bus Connection: The 8255's data bus needs to be connected to the 8086's data bus, allowing data transfer between the microprocessor and the PPI.

• Control Bus Connection: The 8255 requires connections to the 8086's control bus, specifically the read (RD), write (WR), and chip select (CS) signals. These signals control the direction of data transfer and enable the 8255 for communication.

• Power Supply: Both the 8086 and 8255 require a stable power supply with appropriate voltage levels.

2. Software Programming:

• Initialization: Before using the 8255, it must be initialized by programming its control register. This defines the operating mode of each port (A, B, and C). The 8086 uses OUT instructions to write the desired control word to the 8255's control register.

• Port Access: Once initialized, data can be read from or written to the 8255's ports A and B using IN and OUT instructions. Port C's functionality depends on the chosen operating mode.

• Mode Selection: The 8255 supports several modes:

  • Mode 0 (Simple I/O): Each port can be configured as input or output independently.
  • Mode 1 (Strobed I/O): Provides handshaking capabilities for controlled data transfer.
  • Mode 2 (Bidirectional I/O): Allows bidirectional data flow between the 8255 and a peripheral.

• Example Code (Assembly): While a full assembly program is beyond the scope of this blog post, a simplified example might involve:

  ; Initialize 8255 in Mode 0
  MOV AX, control_word ; Control word for Mode 0
  OUT 8255_control_port, AX
  
  ; Write to port A
  MOV AX, data_to_write
  OUT 8255_portA, AX
  
  ; Read from port B
  IN AX, 8255_portB
  ; ...process data in AX...
  

  Remember to replace placeholders like control_word, 8255_control_port, data_to_write, and 8255_portA with actual values relevant to your hardware configuration.

3. Testing and Troubleshooting:

Thorough testing is critical to ensure the 8255 is properly interfaced with the 8086. This might involve using LEDs, switches, or other peripherals to verify data transfer and functionality. Debugging tools and techniques will be essential during the testing process.

Conclusion

Interfacing the 8255 with the 8086 involves careful planning, precise hardware connections, and meticulous software programming. This recipe provides a foundational understanding of the process, enabling you to build upon it for specific application needs. Remember that the intricacies of address decoding and mode selection are highly dependent on the system's architecture and specific peripheral requirements. Understanding these nuances is key to creating a successful and robust interface.