Question

A) What happens when a software Interrupt occurs? Write steps briefly?                                                   

B)  Differentiate between maskable and non-maskable interrupts?

C) How are the multiplexed bus of 8086 demultiplexed?

D) Find the address range when a 2K x 8 memory is interfaced with 8086/8088?

Answer 1

A) When an interrupt occurs, it causes the CPU to stop executing the current program. The control then passes to a special piece of code called an Interrupt Handler or Interrupt Service Routine. The interrupt handler will process the interrupt and resume the interrupted program

The initial program is resumed by the CPU by means of a context switch.

A context switch is the process of storing and restoring state (the context) of a CPU, so that execution can be resumed from the same point at a later time. When an interrupt is generated, the processor saves its execution state via a context switch, and begins executing the interrupt handler at the interrupt vector.

B)1. Maskable Interrupt :
An Interrupt that can be disabled or ignored by the instructions of CPU are called as Maskable Interrupt.The interrupts are either edge-triggered or level-triggered or level-triggered.

eg:-

RST6.5,RST7.5,RST5.5 of 8085 

2. Non-Maskable Interrupt :
An interrupt that cannot be disabled or ignored by the instructions of CPU are called as Non-Maskable Interrupt.A Non-maskable interrupt is often used when response time is critical or when an interrupt should never be disable during normal system operation. Such uses include reporting non-recoverable hardware errors, system debugging and profiling and handling of species cases like system resets.

eg:
Trap of 8085 

C)Step by step answer :-

• Demultiplexing is to separate 2 or more channels that have been multiplexed. Signals are typically multiplexed or combined onto one higher speed channel to efficiently use the bandwidth.

• The 8086 can address 1,114,080 bytes. That does not count I/O space, it only counts memory space.

• there are five addressing modes in 8086 they are : 1->direct addressing 2->Indirect addressing 3->index addressing 4->immediate addressing 5->register addressing.

• The 8086 takes two cycles to fetch words from an odd address because the Bus Interface Unit (BIU) actually only deals with words, which are two bytes at an even address.. If you perform an operation on a byte, the BIU will do a word operation, but it will leave the other byte alone.

D)

Memory Address Decoding

• To determine the address range that a device is mapped into:

This 2KB memory segment maps into the reset location of the 8086/8088 (FFFF0H).