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How Does the 8255 Microprocessor Interface with Peripheral Devices?

What is the 8255 Microprocessor?

A popular integrated circuit intended to interface peripherals with microprocessors is the 8255 microprocessor, sometimes referred to as a programmed peripheral interface (PPI). It includes three parallel 8-bit I/O ports that may be configured for either output or input. To satisfy certain application needs, these ports—named Port A, Port B, and Port C—can be utilized singly or in combination. Furthermore, the 8255 provides multiple operating modes, enhancing its adaptability and appropriateness for an extensive array of uses.

What is the 8255 Microprocessor?
What is the 8255 Microprocessor?

Features and specifications

The 8255 microprocessor is well-suited for peripheral interface since it has several important features and characteristics. It works with the majority of microprocessors and requires only one +5 V supply to operate. Three independently directed 8- bit I/O ports on the device give a variety of interface options. In addition, the 8255 offers versatility and comity with colorful supplemental types by supporting a range of operating modes, including as introductory I/O, strobe I/O, and bidirectional machine I/O. The 8255 microprocessor is a popular choice for bedded systems, consumer electronics, and artificial robotization due to its strong armature and adaptable features.

Peripheral Device Interface

A. Types of peripheral devices supported

Because of its broad supplemental interface armature, the 8255 microprocessor is veritably adaptable to a wide range of operations. It can communicate with a wide range of widgets, including keyboards, defenses, selectors, and sensors. Three 8- bit resemblant I/O ports on the device can be configured to interface with these add-ons. Whether the application requires simple input or output operations or more complex interfacing with multiple devices, the 8255 microprocessor provides the flexibility and capability to meet these requirements efficiently.

B. Modes of operation (I/O, Strobed I/O, and BSR modes)

The 8255 microprocessor supports a variety of operating modes to meet different interface conditions.

  • I/O mode: in this mode, each harborage can be collectively configured as either input or affair.
  • Strobed I/O mode: this mode allows the anchorages to be used for data communication with supplemental bias. The data transfer occurs when a strobe signal is applied to the corresponding harborage.
  • Bit Set/Reset (BSR) mode: in this mode, individual bits of a harborage can be set or reset without affecting the other bits, furnishing lesser inflexibility in controlling peripherals.

These different operating modes allow the 8255 microprocessor to affiliate efficiently with different types of peripherals and perform a wide range of tasks in different operations.

Programming the 8255

A. Overview of programming steps

To set up the 8255 microprocessor’s several operating modes and properly interact with peripherals, programming requires a number of steps.

  • The correct control words must be written to the microprocessor’s control register in order to reset it.

Configuring the ports for the appropriate operating mode—basic, strobed, or BSR—is the next step.

  • At last, the microprocessor is prepared to transmit and receive data between peripherals that are linked to its input/output ports.

B. Example code snippets for different interface modes

  1. Initializing the 8255 in I/O mode:
  2. Initializing the 8255 in I/O mode
  3. Initializing the 8255 in Strobed I/O mode:
  4. Initializing the 8255 in Strobed I/O mode
  5. Initializing the 8255 in BSR mode:
  6. Initializing the 8255 in BSR mode


  1. Industrial Automation: 8255 microprocessors are used by a manufacturing organization to monitor and control many processes. In a conveyor belt system, for instance, the 8255 communicates with sensors to identify items on the belt and manages filling operations to arrange them appropriately. This guarantees a dependable and effective production process.
  2. Home Automation: 8255 microprocessors are used by home automation systems to cover and control outfit like security systems, thermostats, and lighting. The 8255, for case, may communicate with motion sensors to fete movement and acclimate the lighting consequently. In order to shoot security cautions, it can also connect with sensors on windows and doors.
  3. Medical Devices: The 8255 microprocessor interfaces with sensors that assess vital indicators like heart rate, blood pressure, and oxygen saturation in medical equipment like patient monitoring systems. Following its processing, the microprocessor shows the data to medical specialists on a monitor. Furthermore, the 8255 has the ability to regulate filling devices, including infusion pumps, so that patients receive their medication precisely.


Because of its many interface options, the 8255 microprocessor is essential for connecting peripherals and microprocessors in a variety of electronic systems. We have looked at the 8255 microprocessor’s fundamental design, features, and modes of operation throughout this article. We have looked at example code snippets for programming it in various interface modes and explored how it communicates with various peripheral kinds. We have also looked at case studies and real-world applications that demonstrate the value and efficacy of the 8255 microprocessor interface across a range of sectors and disciplines.

Harshvardhan Mishra

Hi, I'm Harshvardhan Mishra. Tech enthusiast and IT professional with a B.Tech in IT, PG Diploma in IoT from CDAC, and 6 years of industry experience. Founder of HVM Smart Solutions, blending technology for real-world solutions. As a passionate technical author, I simplify complex concepts for diverse audiences. Let's connect and explore the tech world together! If you want to help support me on my journey, consider sharing my articles, or Buy me a Coffee! Thank you for reading my blog! Happy learning! Linkedin

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