Latest Technical Interview Answers - 5

Latest Technical Interview Answers - 5

Write about the following instruction :
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Offset of the first instruction of procedure is in two memory addresses in DS. It replaces the contents of IP with contents of word memory locations in DS pointed to by BX.
Write about EVEN directive in 8086 ALP.
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It forces the address of the next byte to be even. 8086 words can be accessed in less time if they begin at even address.
While handling the interrupt instructions in 8086, What are the internal operations may be carried out by the stack?
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(i)SP =SP-2 , stack ß Push flag reg. Contents, IF =0 , TF =0 (ii) SP=SP-2, Stackß CS Reg. Contents, Address of Interrupt pointer = Interrupt type * 4 , CS Register Contents ß Second word of Interrupt pointer (iii) SP=SP-2, Stackß IP, IPß First word of Interrupt pointer
Define LAHF and SAHF instructions in 8086.
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LAHF : Load the 8085 equivalent flags into the AH register. SAHF: Store the AH register into the low order byte of the flag register.
What is the use of TEST instruction in 8086?
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Test instruction is the same as the AND instruction except that ite does not put the result anywhere. Like the CMP instruction , it is used only to set the flags.
What is Emulator?
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Emulator is a mixture of hardware and software .It is used to test and debug the hardware and software of an external system such as the prototype of a microprocessor based instrument.
Define EXTRN directive in in 8086 assembly language?
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The EXTRN directive is used to inform the assembler that the names or labels following the directive are in some other assembly module.
Write the use of Assume directive in 8086 assembly language using one example?
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Assume CS: code_here, DS:data_here It tells the assembler that the logical segment code_here contains the instruction statements for the program and should be treated as a code segment. It also tells the assembler that it should treat the logical segment data_here as the data segment for this program.
Define EQU directive in 8086 assembly language?
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It is used to assign a name to constants used in the programs. Consider the statement ‘corr EQU 07H’ , this would tell the assembler to insert the value 07H everytime that it finds the name corr in the program statement.
How the execution time of an instruction is calculated?
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Execution time of an instruction can be determined by multiplying the number of clock pulses needed to execute the instruction by the clock period.
Write the use of Z bit in opcode?
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It is used by REP instruction. Z bit helps to control the loop. It will be repeated the number of items indicated by the CX register or until Z bit dose not match the Zero flag whichever occurs first.
What is the use of V bit in opcode ?
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It is used by shift and rotate instructions to determine the number of shifts. V bit is set to 0 if the shift count is to be 1. V bit is set to 1 if the CL register contains the shift count.
What is the use of D bit in opcode?
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D bit: It is used in double operand instruction. It is used to indicate whether the register specified by REG is the source operand (D=0) or the destination operand (D=1).
Write about the following instruction : LES CX, [3483H]
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Copy the contents of memory at the displacement of 3483H in DS to CL, contents of 3484H in DS to CH, and copy the contents of memory at displacement of 3485H and 3486H in DS to ES Register.
Write the difference between CBW and CWD instruction in 8086.
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CBW : Convert a byte to a word, sign extend AL Register into a AH Register. CWD : Convert a word to a double word ,sign extend the AX Register into the DX Register
Define Segment Override Prefix.
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Segment Override Prefix : To permit exceptions to the Segment Register usage, a special one byte instruction called a segment override prefix is available . It is of the form :
What is Unpacked BCD Format ?
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Unpacked BCD Format : In Unpacked BCD, there is only one digit per byte and because of this,unpacked multiplication and division can be done. Binary operations act on signle bytes and the results are adjusted. For Division , the adjustment is done before the binary division.
What is AAS instruction in 8086 ?
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Adjust Result of ASCII Subtraction This instruction adjust the binary result of SUB or SBB instruction.
What is the use of Directives in 8086 ?
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Directives in 8086 give directions to the assembler during the assembly process but are not translated into machine instruction.
What is Programmed I/O ?
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Programmed I/O : It consists of continually examining the status of an Interface and performing an I/O operation with the Interface when its status indicates that it has data to be input or its data- out buffer register is ready to receive data from the CPU. .