‘Microprocessors Interview Questions’ Part --6

‘Microprocessors Interview Questions’
What is DAS instruction ?
DAS : Decimal Adjust After Subtraction This instruction converts the binary result of a SUB or SBB instruction in AL to Packed BCD format. It operates only on AL... Read more »
What is the use of ‘W’ bit in opcode ?.
W bit in op-code : If an instruction in 8086 can operate on either a byte or a word , the op-code includes a W-bit which indicates whether a byte ( W =0 ) or a... Read more »
Define XLAT instruction used in 8086.
It translates a byte in AL using a table in memory. The offset address is calculated by adding the 8 bit contents of the AL register and the contents of BX register.... Read more »
What is the use of PUSHF instruction used in 8086 ?
It pushes the flag register contents to the top of the stack. No flags are affected. Read more »
Define Inter segment Indirect addressing mode:
It replaces the contents of IP and CS with the contents of two consecutive words in memory that are referenced by using any of the data related addressing modes... Read more »
Define Inter segment addressing mode:
It replaces the contents of IP with part of the instruction and the contents of CS with another part of the instruction. Read more »
Define Intra segment Indirect addressing mode:
The effective branch address is the contents of a register or memory location that is accessed using any of the data related addressing modes except the immediate... Read more »
Define Intra segment direct addressing mode:
The effective branch address is the sum of an 8- or 16 bit displacement and the current contents of IP. Read more »
Define Based Indexed addressing mode:
The effective address is the sum of a base register and an index register , both of which are specified by the instruction.It is also called as Base related Indexed... Read more »
Define Register relative addressing mode:
The effective address is the sum of an 8- or 16 bit displacement and the contents of a base register or an index register. Read more »
Define Register Indirect Addressing mode:
Effective address of the datum is in the base register BX or an index register that is specified by the instruction. Read more »
Define Register addressing mode:
Datum is in the register that is specified by the instruction E.g : MOV CX,AX (16 bit operand) MOV CL,AL ( 8 bit operand) Read more »
When the Overflow flag is set ?
For addition of 16 bits, this flag is set when there is a carry into the MSB and no carry out of the MSB. Read more »
Write about the auxiliary carry flag used in 8086 ?
It is set if there is a carry out of bit 3 during an addition or a borrow by bit 3 during a subtraction. This flag is used exclusively for BCD arithmetic. Read more »
What is the use of Instruction pointer in 8086 ?
Instruction pointer holds the 16 bit address of the next code byte within the code segment. The value contained in the IP is called effective address or offset.... Read more »