2. 8086 has 2 interrupt inputs 1. NMI 2. INTR For application where we have interrupts from multiple sources, use an external device called a Priority Interrupt Controller(PIC) to “funnel” the interrupt signals into a single interrupt input on the processor.

3. 8259A Overview and system connection Multiply the interrupt type it receives from the 8259A by 4 to produce an address in the interrupt vector table. Push the flags on the stack. Clear IF and TF. Push the return address on the stack. Get the starting address for the interrupt procedure from the interrupt-vector table and load that address in CS and IP. Execute the ISP.

4. 8259A PIC

7. Master and slave Master  The 8259A connected directly into the 8086 INTR pin is called as master Slave  The INT pin from the other 8259A connects into an IR input on the master. This secondary or cascaded device is called as a slave

8. Programming the 8259A The 8259A is programmed by properly initializing: - 4 ICWs - Initialization command words; - 3 OCWs – Operation command words; The initialization procedure may not need to initialize all of them.

9. Initializing an 8259A 1. Find the system base address 2. Find the internal address 3. System address=internal address + base address