Microprocessors Interview Questions of part --17
Can an RC circuit be used as clock source for 8085?
Yes, it can be used, if an accurate clock frequency is not required. Also, the component cost is low compared to LC or Crystal
What are Hardware interrupts?
TRAP, RST7.5, RST6.5, RST5.5, INTR
Which interrupt has the highest priority?
TRAP has the highest priority
What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
How many interrupts are there in 8085?
There are 12 interrupts in 8085.
What does Quality factor mean?
The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
What happens when HLT instruction is executed in processor?
The Micro Processor enters into Halt-State and the buses are tri-stated.
What is Stack Pointer?
Stack pointer is a special purpose 16-bit register in the Microprocessor, which holds the address of the top of the stack.
In 8085 name the 16 bit registers?
Stack pointer and Program counter all have 16 bits.
What are the various flags used in 8085?
Sign flag, Zero flag, Auxiliary flag, Parity flag, Carry flag.
What are Software interrupts?
RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.
Which interrupt is not level-sensitive in 8085?
RST 7.5 is a raising edge-triggering interrupt.
What are level-triggering interrupt?
RST 6.5 & RST 5.5 are level-triggering interrupts.
What is the RST for the TRAP?
RST 4.5 is called as TRAP.
What is Program counter?
Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched. Also Program register keeps the address of the next instruction
Thursday, March 26, 2009
Microprocessors Interview Questionsof part --16
Which Stack is used in 8085?
LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first.
What is the difference between primary & secondary storage device?
In primary storage device the storage capacity is limited. It has a volatile memory. In secondary storage device the storage capacity is larger. It is a nonvolatile memory. Primary devices are: RAM / ROM. Secondary devices are: Floppy disc / Hard disk.
In what way interrupts are classified in 8085?
In 8085 the interrupts are classified as Hardware and Software interrupts.
Name 5 different addressing modes?
Immediate, Direct, Register, Register indirect, Implied addressing modes
In 8085 which is called as High order / Low order Register?
Flag is called as Low order register & Accumulator is called as High order Register.
Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn’t drift with aging. Crystal is used as a clock source most of the times.
What are the various registers in 8085?
Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085
What is meant by a bus?
A bus is a group of conducting lines that carriers data, address, & control signals.
Give examples for 8 / 16 / 32 bit Microprocessor?
8-bit Processor - 8085 / Z80 / 6800; 16-bit Processor - 8086 / 68000 / Z8000; 32-bit Processor - 80386 / 80486
Give an example of one address microprocessor?
8085 is a one address microprocessor.
What is clock frequency for 8085?
3 MHz is the maximum clock frequency for 8085.
Give examples for Micro controller?
Z80, Intel MSC51 &96, Motorola are the best examples of Microcontroller.
Give example for Non-Maskable interrupts?
Trap is known as Non-Maskable interrupts, which is used in emergency condition.
What is the difference between 8086 and 8088?
Trap is known as Non-Maskable interrupts, which is used in emergency condition.
What are the flags in 8086?
In 8086 Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first.
What is the difference between primary & secondary storage device?
In primary storage device the storage capacity is limited. It has a volatile memory. In secondary storage device the storage capacity is larger. It is a nonvolatile memory. Primary devices are: RAM / ROM. Secondary devices are: Floppy disc / Hard disk.
In what way interrupts are classified in 8085?
In 8085 the interrupts are classified as Hardware and Software interrupts.
Name 5 different addressing modes?
Immediate, Direct, Register, Register indirect, Implied addressing modes
In 8085 which is called as High order / Low order Register?
Flag is called as Low order register & Accumulator is called as High order Register.
Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn’t drift with aging. Crystal is used as a clock source most of the times.
What are the various registers in 8085?
Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085
What is meant by a bus?
A bus is a group of conducting lines that carriers data, address, & control signals.
Give examples for 8 / 16 / 32 bit Microprocessor?
8-bit Processor - 8085 / Z80 / 6800; 16-bit Processor - 8086 / 68000 / Z8000; 32-bit Processor - 80386 / 80486
Give an example of one address microprocessor?
8085 is a one address microprocessor.
What is clock frequency for 8085?
3 MHz is the maximum clock frequency for 8085.
Give examples for Micro controller?
Z80, Intel MSC51 &96, Motorola are the best examples of Microcontroller.
Give example for Non-Maskable interrupts?
Trap is known as Non-Maskable interrupts, which is used in emergency condition.
What is the difference between 8086 and 8088?
Trap is known as Non-Maskable interrupts, which is used in emergency condition.
What are the flags in 8086?
In 8086 Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
Microprocessors Interview Questions of part --15
Microprocessors Interview Questions of part --15
Which Stack is used in 8086? k is used in 8086?
FIFO (First In First Out) stack is used in 8086.In this type of Stack the first stored information is retrieved first.
What does EU do?
Execution Unit receives program instruction codes and data from BIU, executes these instructions and store the result in general registers.
What are the various segment registers in 8086?
Code, Data, Stack, Extra Segment registers in 8086.
What are the different functional units in 8086?
Bus Interface Unit and Execution unit, are the two different functional units in 8086.
What is Non-Maskable interrupts?
An interrupt which can be never be turned off (ie. disabled) is known as Non-Maskable interrupt
What is meant by Maskable interrupts?
An interrupt that can be turned off by the programmer is known as Maskable interrupt.
What is the Maximum clock frequency in 8086?
5 Mhz is the Maximum clock frequency in 8086.
Have you studied buses? What types?
There are three types of buses.Address bus: This is used to carry the Address to the memory to fetch either Instruction or Data.Data bus : This is used to carry the Data from the memory.Control bus : This is used to carry the Control signals like RD/WR, Select etc.
How many bit combinations are there in a byte?
Byte contains 8 combinations of bits.
Where does CPU Enhanced mode originate from?
Intel’s 80386 was the first 32-bit processor, and since the company had to backward-support the 8086. All the modern Intel-based processors run in the Enhanced mode, capable of switching between Real mode (just like the real 8086) and Protected mode, which is the current mode of operation.
Name the processor lines of two major manufacturers?
High-end: Intel - Pentium (II, III, 4), AMD - Athlon. Low-end: Intel - Celeron, AMD - Duron. 64-bit: Intel - Itanium 2, AMD - Opteron
What is 1st / 2nd / 3rd / 4th generation processor?
The processor made of PMOS / NMOS / HMOS / HCMOS technology is called 1st / 2nd / 3rd / 4th generation processor, and it is made up of 4 / 8 / 16 / 32 bits.
What are the various registers in 8085?
Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085
What is Program counter?
Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched. Also Program register keeps the address of the next instruction.
Which Stack is used in 8085?
LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first
Which Stack is used in 8086? k is used in 8086?
FIFO (First In First Out) stack is used in 8086.In this type of Stack the first stored information is retrieved first.
What does EU do?
Execution Unit receives program instruction codes and data from BIU, executes these instructions and store the result in general registers.
What are the various segment registers in 8086?
Code, Data, Stack, Extra Segment registers in 8086.
What are the different functional units in 8086?
Bus Interface Unit and Execution unit, are the two different functional units in 8086.
What is Non-Maskable interrupts?
An interrupt which can be never be turned off (ie. disabled) is known as Non-Maskable interrupt
What is meant by Maskable interrupts?
An interrupt that can be turned off by the programmer is known as Maskable interrupt.
What is the Maximum clock frequency in 8086?
5 Mhz is the Maximum clock frequency in 8086.
Have you studied buses? What types?
There are three types of buses.Address bus: This is used to carry the Address to the memory to fetch either Instruction or Data.Data bus : This is used to carry the Data from the memory.Control bus : This is used to carry the Control signals like RD/WR, Select etc.
How many bit combinations are there in a byte?
Byte contains 8 combinations of bits.
Where does CPU Enhanced mode originate from?
Intel’s 80386 was the first 32-bit processor, and since the company had to backward-support the 8086. All the modern Intel-based processors run in the Enhanced mode, capable of switching between Real mode (just like the real 8086) and Protected mode, which is the current mode of operation.
Name the processor lines of two major manufacturers?
High-end: Intel - Pentium (II, III, 4), AMD - Athlon. Low-end: Intel - Celeron, AMD - Duron. 64-bit: Intel - Itanium 2, AMD - Opteron
What is 1st / 2nd / 3rd / 4th generation processor?
The processor made of PMOS / NMOS / HMOS / HCMOS technology is called 1st / 2nd / 3rd / 4th generation processor, and it is made up of 4 / 8 / 16 / 32 bits.
What are the various registers in 8085?
Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085
What is Program counter?
Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched. Also Program register keeps the address of the next instruction.
Which Stack is used in 8085?
LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first
Sunday, March 22, 2009
Microprocessors Interview Questions o part ---14
Microprocessors Interview Questions of part ---14
What happens when HLT instruction is executed in processor?
The Micro Processor
enters into Halt-State and the buses are tri-stated.
What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
In 8085 which is called as High order / Low order Register?
Flag is called as Low order register & Accumulator is called as High order Register.
Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn’t drift with aging. Crystal is used as a clock source most of the times.
What are the flags in 8086?
In 8086 Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
What is a Microprocessor?
Microprocessor is a program-controlled device, which fetches the instructions from memory, decodes and executes the instructions. Most Micro Processor
are single- chip devices.
How do you submit a form using JavaScript?
Use document.forms[0].submit()(0 refers to the index of the form – if we have more than one form in a page, then the first one has the index 0, second has index 1 and so on).
Write about the following instruction :
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.
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?
(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.
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?
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?
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?
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?
Assume CS: code_here, DS:data_hereIt 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.
What happens when HLT instruction is executed in processor?
The Micro Processor
enters into Halt-State and the buses are tri-stated.
What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
In 8085 which is called as High order / Low order Register?
Flag is called as Low order register & Accumulator is called as High order Register.
Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn’t drift with aging. Crystal is used as a clock source most of the times.
What are the flags in 8086?
In 8086 Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
What is a Microprocessor?
Microprocessor is a program-controlled device, which fetches the instructions from memory, decodes and executes the instructions. Most Micro Processor
are single- chip devices.
How do you submit a form using JavaScript?
Use document.forms[0].submit()(0 refers to the index of the form – if we have more than one form in a page, then the first one has the index 0, second has index 1 and so on).
Write about the following instruction :
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.
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?
(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.
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?
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?
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?
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?
Assume CS: code_here, DS:data_hereIt 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.
Microprocessors Interview Questions of part --13
Microprocessors Interview Questions of part --13
Define EQU directive in 8086 assembly language?
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?
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?
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 ?
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?
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]
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.
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.
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 ?
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 ?
Adjust Result of ASCII SubtractionThis instruction adjust the binary result of SUB or SBB instruction.
What is the use of Directives in 8086 ?
Directives in 8086 give directions to the assembler during the assembly process but are not translated into machine instruction.
What is Programmed I/O ?
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.
Write about the following instruction :
MOV CS:[BX], DLMOV CS:[BX],DL - It copies a byte from DL Register. Effective Address for the memory location is contained in the BX Register. Normally an effective address in BX will be added to the data segment base in DS to produce the physical memory address. In this instruction CS: indicates that we want the BIU to add the effective address to the code segment base in CS to produce the physical address.
What is difference between DIV and IDIV instruction in 8086 ?
DIV : It operates only on unsigned number.IDIV : It operates only on signed numbers.
What is Packed BCD Format ?
Packed BCD Format : Packed BCD Numbers are stored in two digits to a byte , in 4 bit groups referred to as nibbles. ALU is capable of performing only binary addition and subtraction , but by adjusting the sum or difference the correct result in packed BCD format.
Define EQU directive in 8086 assembly language?
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?
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?
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 ?
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?
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]
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.
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.
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 ?
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 ?
Adjust Result of ASCII SubtractionThis instruction adjust the binary result of SUB or SBB instruction.
What is the use of Directives in 8086 ?
Directives in 8086 give directions to the assembler during the assembly process but are not translated into machine instruction.
What is Programmed I/O ?
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.
Write about the following instruction :
MOV CS:[BX], DLMOV CS:[BX],DL - It copies a byte from DL Register. Effective Address for the memory location is contained in the BX Register. Normally an effective address in BX will be added to the data segment base in DS to produce the physical memory address. In this instruction CS: indicates that we want the BIU to add the effective address to the code segment base in CS to produce the physical address.
What is difference between DIV and IDIV instruction in 8086 ?
DIV : It operates only on unsigned number.IDIV : It operates only on signed numbers.
What is Packed BCD Format ?
Packed BCD Format : Packed BCD Numbers are stored in two digits to a byte , in 4 bit groups referred to as nibbles. ALU is capable of performing only binary addition and subtraction , but by adjusting the sum or difference the correct result in packed BCD format.
Microprocessors Interview Questions of part -------12
Microprocessors Interview Questions of part ----12
What is DAS instruction ?
DAS : Decimal Adjust After SubtractionThis instruction converts the binary result of a SUB or SBB instruction in AL to Packed BCD format. It operates only on AL Register.
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 word (W =1) is being accessed.
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. BX register contains the starting offset address of the Lookup table . After execution , corresponding data memory contents of the lookup table are loaded into the AL register.
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.
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 except immediate and register modes
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.
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 mode. The contents of IP are replaced by the effective branch address.
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.
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 addressing.
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.
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.
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)
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.
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.
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. It contains the distance from the base address to the next instruction byte to be fetched.
What is DAS instruction ?
DAS : Decimal Adjust After SubtractionThis instruction converts the binary result of a SUB or SBB instruction in AL to Packed BCD format. It operates only on AL Register.
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 word (W =1) is being accessed.
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. BX register contains the starting offset address of the Lookup table . After execution , corresponding data memory contents of the lookup table are loaded into the AL register.
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.
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 except immediate and register modes
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.
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 mode. The contents of IP are replaced by the effective branch address.
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.
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 addressing.
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.
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.
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)
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.
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.
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. It contains the distance from the base address to the next instruction byte to be fetched.
Tuesday, March 17, 2009
Microprocessors Interview Questions part ---------11
Microprocessors Interview Questions part ------11
Which interrupt is not level-sensitive in 8085?
RST 7.5 is a raising edge-triggering interrupt.
What are Software interrupts?
RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.
What are the various flags used in 8085?
Sign flag, Zero flag, Auxillary flag, Parity flag, Carry flag.
In 8085 name the 16 bit registers?
Stack pointer and Program counter all have 16 bits.
What is Stack Pointer?
Stack pointer is a special purpose 16-bit register in the Microprocessor, which holds the address of the top of the stack.
What happens when HLT instruction is executed in processor?
The Micro Processor enters into Halt-State and the buses are tri-stated.
What does Quality factor mean?
The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
How many interrupts are there in 8085?
There are 12 interrupts in 8085.
What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
Which interrupt has the highest priority?
TRAP has the highest priority
What are Hardware interrupts?
TRAP, RST7.5, RST6.5, RST5.5, INTR
Can an RC circuit be used as clock source for 8085?
Yes, it can be used, if an accurate clock frequency is not required. Also, the component cost is low compared to LC or Crystal
Which interrupt is not level-sensitive in 8085?
RST 7.5 is a raising edge-triggering interrupt.
What are Software interrupts?
RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.
What are the various flags used in 8085?
Sign flag, Zero flag, Auxillary flag, Parity flag, Carry flag.
In 8085 name the 16 bit registers?
Stack pointer and Program counter all have 16 bits.
What is Stack Pointer?
Stack pointer is a special purpose 16-bit register in the Microprocessor, which holds the address of the top of the stack.
What happens when HLT instruction is executed in processor?
The Micro Processor enters into Halt-State and the buses are tri-stated.
What does Quality factor mean?
The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
How many interrupts are there in 8085?
There are 12 interrupts in 8085.
What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
Which interrupt has the highest priority?
TRAP has the highest priority
What are Hardware interrupts?
TRAP, RST7.5, RST6.5, RST5.5, INTR
Can an RC circuit be used as clock source for 8085?
Yes, it can be used, if an accurate clock frequency is not required. Also, the component cost is low compared to LC or Crystal
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