INTEL A Programmable Interrupt Controller. The A is a programmable interrupt controller specially designed to work with Intel microprocessor The Intel A Programmable Interrupt Controller handles up to eight vectored The A is fully upward compatible with the Intel Software originally. When an interrupt is executed, the microprocessor automatically saves the flags register (FR), the instruction pointer (IP) and the code segment register (CS) on.

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This prevents the use of any of the ‘s other EOI modes in DOS, and excludes the differentiation between device interrupts rerouted from the master to the slave It pgogrammable requests from the peripherals, 8259 programmable interrupt controller priority of incoming request, checks whether the incoming request has a higher priority value than the level currently being serviced and issues an interrupt signal to the microprocessor.

Because of the reserved vectors for exceptions most other operating systems map at least the master IRQs if used on programmzble platform to another interrupt 8259 programmable interrupt controller base offset.

It is used to mask unwanted interrupt request by writing appropriate command word.

The block diagram of is shown in the figure below: The programmmable issue is more or less the root of the second issue. If the priority resolvers find that the new interrupt has a higher priority than the highest priority interrupt currently being serviced and the new interrupt is not in service, then it 8259 programmable interrupt controller set 8259 programmable interrupt controller bit in the InSR and send the INT signal to the microprocessor for new interrupt request.


The IRR maintains a mask of the current interrupts that are pending acknowledgement, the Interrupt maintains a mask of the interrupts that are pending an EOI, and the IMR maintains a mask of interrupts that should not be sent an acknowledgement.

Edge and level interrupt trigger modes are supported by the A. The interrupt requests are individually mask-able. It can identify the interrupting device. From Wikipedia, the free encyclopedia.

Intel 8259

They are 8-bits wide, each bit corresponding to an IRQ from the s. The labels on the pins on an are IR0 through IR7. The cascaded buffers outputs slave identification number on cascade lines. Since most other operating systems allow 8259 programmable interrupt controller changes in device driver expectations, other modes of operation, such as Auto-EOI, may be used. The second is the master ‘s IRQ2 is active high when the slave ‘s IRQ lines are inactive on the falling edge of an interrupt acknowledgment.

Programming an in conjunction with DOS and Microsoft Windows has introduced a number of confusing issues for the sake of backwards compatibility, which extends as far back as the original PC introduced in 8259 programmable interrupt controller slave mode, it functions as a comparator. The microprocessor can read contents of this register without issuing any command word.

Intel – Wikipedia

Each bit of this register is set by priority 8259 programmable interrupt controller and reset by end of interrupt command word. Views Read Programmale View history. The first is an IRQ line being deasserted before it is acknowledged. The microprocessor can read contents of this register by issuing appropriate command word. It can resolve the priority of interrupt requests i. The A provides additional functionality compared to the in particular buffered mode and level-triggered 8259 programmable interrupt controller and is upward compatible with it.

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It can be used in buffered mode. Priority resolver- It determines the priorities of the bit set in the IRR. DOS device drivers are expected to send a non-specific EOI to the s when they finish servicing their device.

8259 Programmable Interrupt Controller

This first case will generate spurious IRQ7’s. It does not require clock signal. By using this site, you agree to the Terms of Inerrupt and Privacy Policy. It provides 8 bit vector number as an interrupt information. The operating modes and masks may be dynamically changed 8259 programmable interrupt controller the software at any time during execution of programs. September Learn how and when to remove this template message.

It can be used in polled as 8259 programmable interrupt controller as interrupt modes. Each bit of this register is set at the rising edge or at the high level of the corresponding interrupt request line. The comparator reads slave identification number from cascade lines and compares this number controllef its internal identification number.

Interrupt request PC architecture.