Maskable Interrupt: An Interrupt that can be disabled or ignored by the instructions of CPU are called as Maskable Interrupt. 

  1. Interrupt signals which can be ignored by processor, while processor doing crucial job it will ignore these kind of interrupts and continue in its state.
  2. Typically your processor might allow multiple interrupt sources, but your design only requires some of them.
  3. Maskable interrupts are interrupts that can be blocked. Masking can be done by software or hardware means.

Eg: RST6.5,RST7.5,RST5.5 OF 8085 are maskable Interrupts.

Non-Maskable Interrupt: An interrupt that cannot be disabled or ignored by the instructions of CPU are called as Non-Maskable Interrupt.

  1. These Interrupt signals will be not ignored and given attention all the time.
  2. Typically these are used for CRITICIAL or FATAL conditions, or for system reset functions.
  3. Non-maskable interrupts are interrupts that are always recognized; the corresponding ISRs are executed.

Eg: TRAP of 8085

Polled Interrupt: Polled interrupt are handled using software and are therefore slower compared to vectored(hardware) interrupts. In this method there is one common branch address for all interrupts. The program that takes care of interrupts begins at the branch address and polls the interrupts sources in sequence. The order in which they are tested determines the priority of each interrupt. The highest priority source is  tested first, and if its interrupt signal is on, control branches to a service routine for this source; otherwise the next lower priority sources is tested. & so on. Polled interrupt are very simple But or large no. of devices, the time required to poll each device may exceed the service to the device. In such case, the faster mechanism called chained interrupt is used. 

Fig:



Vectored and Non-Vectored Interrupts : Vectored interrupts require the IVA to be supplied by the external device that gives the interrupt signal. This technique is vectoring, is implemented in number of ways.  Non-vectored interrupts have fixed IVA for ISRs of different interrupt signals. 

Software and Hardware Interrupts: Software interrupts are special instructions, after execution transfer the control to predefined ISR.  Hardware interrupts are signals given to the processor, for recognition as an interrupt and execution of the corresponding ISR.