Block Diagram of 8259 Microprocessor

The 8259 Programmable Interrupt Controller (PIC) is a microprocessor peripheral used to manage interrupts in a system. It helps in handling multiple interrupt requests (IRQs) and sending the interrupt service routines (ISRs) to the microprocessor.

The 8259 Microprocessor refers to the Intel 8259 Programmable Interrupt Controller (PIC) which is an important component used in managing interrupt requests (IRQs) in a microprocessor-based system. It was designed to handle multiple interrupt sources and prioritize them, allowing for more efficient processing of interrupts in systems with limited interrupt lines.

• 8259 microprocessor can be programmed according to given interrupts condition and it can be provided either with level or edge-triggered interrupt level.
• It can be programmed to either work in 8085 or in 8086 microprocessors.
• Individual interrupt bits can be masked.
• By cascading Nine 8259's in Master-Slave Configuration we can handle up to 64 interrupt pins.

Read more about 8259 PIC Microcontroller.

Features of 8259 Microprocessor

• Interrupt Prioritization: The 8259 can decide which interrupt is more important and should be handled first.
• Interrupt Masking: It can block certain interrupts, stopping them from being processed when needed.
• Status Registers: It keeps track of which interrupts are active and whether any interrupts are blocked.
• Interrupt Mask Register (IMR): It controls which interrupts are allowed and which are blocked by setting specific bits.
• Compatibility with 8085 and 8086: The 8259 works with older microprocessors like 8085 and 8086 to manage interrupts.

It contains 3 registers commonly known as ISR, IRR, IMR & there is 1 priority resolver (PR). 

• Interrupt Request Register (IRR): It stores those bits which are requested for their interrupt services.
• Interrupt Service Register (ISR): It stores the interrupt levels which is currently being served.
• Interrupt Mask Register (IMR): It stores interrupt levels that have to be masked. These interrupt levels are already accepted by the 8259 microprocessor.

Priority Resolver (PR): It examines all the 3 registers and sets the priority of interrupts and sets the interrupt levels in ISR which has the highest priority and the rest of the interrupt bit is IRR which is already accepted. 

SP/EN (low active pin): If its value is 1 it works in master mode & if its value=e is 0 then it works in slave mode. 

Cascade Buffer: It is used to cascade more number of Programmable Interrupt Controller to increase the interrupts handling capability up to 64 levels. 

Advantages of 8259 Microprocessor

• Interrupt management: The 8259 microprocessor is a specialized chip that is dedicated to managing interrupts, which can help to improve system performance and reduce the workload on the main CPU.
• Programmability: The 8259 microprocessor is programmable, which means that it can be customized to handle specific types of interrupts and to prioritize different interrupt requests.
• Compatibility: The 8259 microprocessor is compatible with a wide range of microprocessors, making it a popular choice for interrupt management in many different systems.
• Multiple interrupt inputs: The 8259 microprocessor can handle multiple interrupt inputs, which makes it a useful peripheral for managing complex systems with multiple devices.
• Ease of use: The 8259 microprocessor includes simple interface pins and registers, making it relatively easy to use and program.

Disadvantages of 8259 Microprocessor

• Cost: While the 8259 microprocessor is relatively affordable, it does add cost to a system, particularly if multiple 8259s are required.
• Limited functionality: While the 8259 microprocessor is a useful peripheral for interrupt management, it does not include more advanced features, such as DMA (direct memory access) or advanced error correction.
• Limited number of interrupts: The 8259 microprocessor can only handle a limited number of interrupt requests at once, which may be insufficient for some applications.
• Complex programming: Although the interface pins and registers of the 8259 microprocessor are relatively simple, programming the 8259 can be complex, requiring careful attention to interrupt prioritization and other parameters.

Applications of 8259 Microprocessor

• Interrupt Management: It manages and prioritizes interrupt requests in microprocessor systems.
• Prioritization: It allows prioritization of multiple interrupt requests from devices.
• Multi-Processor Systems: It manages interrupts in systems with multiple processors.
• Real-Time Systems: It ensures timely responses to external events in real-time applications.
• Peripheral Management: It handles interrupts from peripherals like sensors and motors.