Microprocessors Interview Questions part --7

List the functions of Bus Interface Unit in 8086.
Sends out addressesFetches instructions from memoryReads data from ports and memoryWrites data to port and memory

List the branch related addressing mode:
Intra segment DirectIntra segment IndirectInter segment DirectInter Segment Indirect
Define Relative based indexed addressing mode:

Relative Based Indexed Addressing Mode : Effective Address is calculated by the sum of 8- or 16 bit displacement and a based indexed address.
E.A.= (BX or BP) + (SI or DI) +( 8 bit displacement (sign extended ) or 16 bit displacement)
Physical Address= E.A + (DS)*1610

Define Direct Addressing

A 16 bit offset address of the data memory location is specified with reference to the DS segment starting address.For.E.g MOV [1020H],5020H instruction transfers a word 5020H to the data memory location at 11020H if DS=1000H.

Define Immediate Addressing.
An 8 bit or 16 bit immediate data follows the instruction. For e.g MOV AX,5020H instruction transfers a word 5020H to the AX register .

Define Register Relative Addressing Mode.
Register Relative Addressing Mode : The Effective Address is Calculated by the sum of 8- or 16 bit displacement and the contents of a base Register or an index Register.
E.A. = content of(BX or BP or SI or DI) + (8 bit displacement (sign extended ) or 16 bit displacement
Physical Address = E.A +(DS)*1610

Compare the 8 bit microprocessors 8080A and 8085.
8080A is the predecessor of 8085. 8085 has the instruction set of 8080A plus some additional ones. Program written for 8080A will be executed by 8085. 8085 and 8080A are not pin compatible. Both require a +5V power supply

What are the limitations of 8085 MPU?
(i) The lower order address bus of the 8085 microprocessor is multiplexed (time shared) with the data bus. The buses need to be demultiplexed.
(ii) Appropriate control signals need to be generated to interface memory and I/O with the 8085.
Write about RST pins in 8085?
In 8085 ,three RST pins are available, such as RST 7.5 ,RST 6.5 , RST 5.5
RST represents Restart Interrupts. These are vectored interrupts that transfer the program control to specific memory locations. They have higher priorities than the INTR interrupt. Among these three, the priority order is 7.5,6.5,5.5.

List the four operations commonly performed by MPU( Micro processing Unit)?
Memory Read : Reads data (or instructions) from memory.Memory Write: Writes Data (or instructions) into memory.I/O Read: Accepts data from input devices
.I/O Write: Sends data to output devices

What is compiler?
Compiler is a program that translates English like words of a high level language into the machine language of a computer. A compiler read a given program ,called a source code, in its entirely and then translates the program into the machine language, which is called an Object Code.

What do you mean ‘ Data Width’?
Data Width is the width of the ALU. An 8 bit ALU can add / subtract/ multiply etc.. two 8 bit numbers . In many cases, the external data bus is the same width as the ALU, but not always. The 8088 had a 16 bit ALU and 8 bit bus , while the modern
List the limitations of 8 bit microprocessor:
Lower Execution Speed
It can address less memory size
Few instructions are available
Define Real Time
Real Time Systems are those in which timeliness is as important as the correctness of the outputs, although this does not mean that they have to be “fast systems”.