What is Registers used in 8259?

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The 8259 is a programmable interrupt controller. It was designed to manage multiple interrupt requests from various peripheral devices in a computer system. 8259 is a programmable interrupt controller which has a unique style. Some certain interrupt conditions regulate the interrupt levels as well. These interrupt levels are also known as the edge-triggered interrupt where the masking process is related to the individual interrupt bits with 64 pins. In this article, we are going to discuss the Registers used in 8259 in detail.

There are three major registers used in 8259. These registers are mainly used to handle the priority schemes. It means the registers present in the 8259 accept the edge-triggered or level-triggered interrupt signals to process them further. Here is the detailed information of those registers as mentioned below.

Registers used in 8259	Description
Interrupt Request Register (IRR)	Interrupt Request Register (IRR) requests the interrupt services by storing the interrupt levels of the operation. It holds the interrupt requests from the peripheral devices. Every bit of this register line corresponds to one of the eight interrupt lines i.e. IR0-IR7. The priority resolver checks the IRR continuously to determine the priority of the interrupt.
In-Service Register (ISR)	In-Service Register (ISR) stores the interrupt levels related to the current operations. Every bit of the In-Service Register (ISR) corresponds to one of the eight interrupt lines i.e. IR0-IR7. End of Interrupt (EOI) takes place when a particular interrupt request is being serviced and cleared completely. In-service register (ISR) always ensures that PIC will not acknowledge the same interrupt request until it resolves completely.
Interrupt Mask Register (IMR)	Interrupt Mask Register (IMR) performs the masking and unmasking process. The Interrupt Mask Register (IMR) corresponds to one of the eight interrupt lines. Interrupt Mask Register (IMR) sets a mask value for each interrupt which prevents acknowledge of the same interrupt request until it resolves completely. The Interrupt Mask Register (IMR) allows the CPU to ignore the specific interrupts through a selective process via masking.

Registers used in 8259

Description

Interrupt Request Register (IRR)

Interrupt Request Register (IRR) requests the interrupt services by storing the interrupt levels of the operation.

It holds the interrupt requests from the peripheral devices.

Every bit of this register line corresponds to one of the eight interrupt lines i.e. IR0-IR7.

The priority resolver checks the IRR continuously to determine the priority of the interrupt.

In-Service Register (ISR)

In-Service Register (ISR) stores the interrupt levels related to the current operations.

Every bit of the In-Service Register (ISR) corresponds to one of the eight interrupt lines i.e. IR0-IR7.

End of Interrupt (EOI) takes place when a particular interrupt request is being serviced and cleared completely.

In-service register (ISR) always ensures that PIC will not acknowledge the same interrupt request until it resolves completely.

Interrupt Mask Register (IMR)

Interrupt Mask Register (IMR) performs the masking and unmasking process.

The Interrupt Mask Register (IMR) corresponds to one of the eight interrupt lines.

Interrupt Mask Register (IMR) sets a mask value for each interrupt which prevents acknowledge of the same interrupt request until it resolves completely.

The Interrupt Mask Register (IMR) allows the CPU to ignore the specific interrupts through a selective process via masking.

Here is the block diagram of the 8259 microprocessor as mentioned below.

block diagram of the 8259 microprocessor

Here are the advantages of the 8259 as mentioned below.

The 8259 prioritizes multiple interrupt requests.
It can be expanded to handle more than 8 interrupts.
The 8259 provides vector addresses for ISRs.
It is programmable for flexible interrupt management.
Using the 8259 reduces CPU overhead in handling interrupts.

Here are the disadvantages of the 8259 as mentioned below.

The 8259 requires additional hardware setup.
It is limited to 8 interrupts without cascading.
Adding the 8259 can complicate the system design.
It introduces slight latency in interrupt handling.
Configuring the 8259 requires programming knowledge.

Here are the applications of the 8259 as mentioned below.

Keyboard input management.
Mouse input handling.
Serial communication.
Parallel port management.
Disk drive operations.

The 8259 programmable interrupt controller is a key element in microprocessor systems, playing a pivotal role in managing numerous interrupt sources. The IRR and ISR along with IMR used in the 8259 to sort out the priority of the interrupts very efficiently. With this knowledge we can now see how the microprocessor ensures that it is able to handle all these tasks so as to allow smooth operation of the whole system which has been presented in this article.

What are the registers available in 8259?

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

What is 8259 used for?

The 8259 combines multiple interrupt input sources. It binds all the interrupts into a single interrupt output. It is also considered as the host microprocessor.

How many pins are in 8259?

Intel 8259 is designed as a 28-pin-programmable IC. It is available as a package named DIP or the Dual inline package.

Registers used in 8259