What is the need for 8259 pic?

PIC 8259 is a Programmable Interrupt Controller that can work with 8085, 8086 etc. It is used to increase the number of interrupts. A single 8259 provides 8 interrupts while a cascaded configuration of 1 master 8259 and 8 slave 8259s can provide up to 64 interrupts.

What is the function of programmable interrupt controller?

In computing, a programmable interrupt controller (PIC) is an integrated circuit that helps a microprocessor (or CPU) handle interrupt requests (IRQ) coming from multiple different sources (like external I/O devices) which may occur simultaneously.

What are the operating modes of 8259A?

After initialization, the 8259A operates in fully nested mode so it is called default mode. The 8259 continues to operate in the Fully Nested Mode until the mode is changed through Operation Command Words. In this mode, IR0 has highest priority and IR7 has lowest priority.

How many interrupts can be handled maximum by cascading?

64 interrupt
We can increase interrupt handling capability upto 64 interrupt level by cascading further 8259 PIC. Clock cycle is not required.

Is 8259 and 8259A same?

The 8259A is upward compatible with 8259. The main difference between the two is that the 8259A can be used with Intel 8086/8088 processor. It also includes additional features such as level triggered mode, buffered mode and automatic end of interrupt mode.

What is the advantage of cascade mode in 8259?

The priority of interrupts is decided by the different operating modes. We know that a single 8259 can handle 8 interrupt inputs but by cascading multiple 8259, it can handle maximal 64 interrupt inputs. 8259 allows individual masking of each generated interrupt using interrupt mask register.

What are priority modes of 8259?

Its priority structure is fixed and is the same as fully nested mode (i.e. IR0 has the highest priority and IR7 has the lowest priority). In a special fully nested mode, the master will only serve higher priority interrupt from a slave, whose another interrupt is currently in service.

Which are the different interrupt sources for PIC and priorities assigned to the interrupts of PIC?

Priority bits : select high or low priority. INT0IF: This is External Interrupt 0 (INT0) flag bit. INT0IE: This bit enables/disables the External Interrupt 0. PEIE/GIEL: This bit is used to enable/disable all the peripheral interrupts (Internal interrupts) of the controller.

What is the difference between IMR ISR and IRR registers?

Interrupt Request Register (IRR): It stores those bits which are requesting for their interrupt services. Interrupt Service Register (ISR): It stores that interrupt levels which is currently being servied. Interrupt Mask Register (IMR): It stores that interrupt levels which have to be masked.

Which of the following is used in cascading mode of 8259A?

Cascade Lines : A signal 8259A provides eight vectored interrupts. If more interrupts are required, the 8259A is used in cascade mode. In cascade mode, a master 8259A along with eight slaves 8259A can provide upto 64 vectored interrupt lines. These three lines act as select lines for addressing the slave 8259A.

What is 8259 PIC microprocessor?

8259 PIC Microprocessor 1 This chip is designed for 8085 and 8086. 2 It can be programmed either in edge triggered, or in level triggered mode 3 We can mask individual bits of Interrupt Request Register. 4 By cascading 8259 chips, we can increase interrupts up to 64 interrupt lines 5 Clock cycle is not needed.

How to increase the interrupt handling capability of Pic 8259?

But by connecting 8259 with CPU, we can increase the interrupt handling capability. 8259 combines the multi interrupt input sources into a single interrupt output. Interfacing of single PIC provides 8 interrupts inputs from IR0-IR7.

How many interrupts are there in 8259 microprocessor?

The 8259 is known as the Programmable Interrupt Controller (PIC) microprocessor. In 8085 and 8086 there are five hardware interrupts and two hardware interrupts respectively.

How 8259 responds to the request made by other microprocessor?

If 8259 is enabled, and the other microprocessor Interrupt flag is high then this causes the value of the output INT pin high and in this way 8259 responds to the request made by other microprocessor. It stores all the interrupt level which are requesting for Interrupt services. It stores the interrupt level which are currently being executed.