1. Interrupt-Driven I/O There are different types of interrupts –Hardware Generated by the 8259 PIC – signals the CPU to suspend execution of the current program and process the interrupt (keyboard, serial port) Occasionally, programs must disable hardware interrupts when performing sensitive operations on segment registers and the stack. Use CLI (Clear Interrupt flag) to disable interrupts and STI (Set interrupt flag) to enable interrupts. –Software Not really an interrupt (INT) –Internal Interrupts Divide by zero Traps

2. Responding to Interrupts

3. Hardware Interrupt Pins NMI – non-maskable interrupt – it cannot be blocked (the CPU must respond) – reserved for critical system functions. INTR – maskable via the IF flag.