Interrupt

Interrupt
An interrupt is any service request that causes the CPU to stop its current execution stream and to execute an instruction stream and to execute an instruction stream that services the interrupt
When the CPU finishes servicing the interrupt, it returns to the original execution stream at the point where it left off.
Hardware interrupt
If an interrupt is initiated in a processor by an appropriate signal at the
interrupt pin, then the interrupt is called Hardware interrupt.
Software interrupts
the Software interrupts are program instructions. These instructions
are inserted at desired locations in a program. While running a program, if software interrupt instruction is encountered then the processor executes an interrupt service routine.
What is the difference between Hardware and Software interrupt?
The Software interrupt is initiated by the main program, but the
Hardware interrupt is initiated by an external device.
In 8085, the Software interrupt cannot be disabled or masked but the
Hardware interrupt except TRAP can be disabled or masked
Interrupts provide a mechanism of transferring control from a foreground process (the current executing program) to an
Service Routine. When such a transfer is initiated by the hardware in response to special internal or external conditions, a hardware interrupt is said to have occurred. External hardware interrupts are generated by peripheral devices and are the main mechanism used by these devices to get the attention of the processor. Certain external hardware interrupts are maskable in that they may be disabled by clearing the Interrupt enable flag (IF) in the flags register. External hardware interrupts that cannot be disabled by clearing IF are called non-maskable interrupts. Typically, non-maskable interrupts are hardware events that must be responded to immediately by the CPU. An example of such an event is the occurrence of a memory or I/O parity error.
Internal hardware interrupts are hardware interrupts that are generated internally to the processor, generally on the occurrence of an error condition. A software interrupt occurs when an INT instruction is executed. With a software interrupt, the type of the interrupt is specified in the INT instruction. With hardware interrupts, the type of the interrupt is supplied by the interrupting hardware. In both cases, when an interrupt occurs, the addresses specified in the related interrupt vector are used to set the CS and IP registers with the starting segment : offset address of the associated interrupt service routine. It is this routine which performs whatever functions necessary is servicing the interrupt. The same sequence of events as was explained for the mechanism of the INT instruction, happens in the case of hardware interrupts.There are 256 possible interrupt types available on the IBM PC with certain of these reserved for various system purposes, and certain available for user-defined interrupt service routines.
External Interrupts