QUESTION-BANK
Q1. Differentiate between microprocessor and
microcontroller?
Ans. 1. Microprocessor is a general purpose
devise
2. Microcontroller is indented for a specific
purpose
3. Memory ,I/O devices etc need to be
interfaced with microprocessor
4. Microcontroller is having its own memory ,
I/O etc integrated with it
5. We can say that microprocessor is a cpu on
a chip
6.
Microcontroller is a system on a chip
Q2. What is an instruction queue? Explain?
Ans. This is introduced in 8086 processor.This
queue is in the BIU and is used for storing the predecoded instructions.This
will overlap the fetching and execution cycle.
The E U will take the instructions from the queue for
decoding and execution.
Q3. What is REP prefix? How it functions for
string instructions?
Ans. This REP prefix is used for repeating.
The instruction with REP prefix will execute repeatedly till the count in the
cx register will be zero. This can be used in with some of the string handling
instructions.
Q4. Explain the instructions (i) LDS (ii) PUSHF
(iii) TEST (iv) CLD
Ans.
i)
LDS : load pointer to DS
Move a 32 bit content
from the memory given as source to 16
bit destination
register specified and to DS register.
ii)
PUSHF
: push the flag
After the
execution the content of the flag register will be
pushed to the
stack.The higher byte to sp-1 and lower to
sp-2
iii)
TEST : logical comparison
This will compare
the source and the destination specified.
The result will be
reflected only in the flag registers.
iv)
CLD : this will clear the
direction flag.
Q5. What is stack? Explain the use and operation
of stack and stack pointer?
Ans. A stack is a portion of the memory used for the
temporary storage. A stack is a last
In first Out
memory. A stack grows in the decreasing order. A stack will hold the
temporary
information’s push and pop are the instructions used for storing and
accessing
data from the stack. Contents can be moved as 16 bit only using push and
pop
instructions.
Q6. What are the flags in 8086?
Ans. In 8086 Carry flag, Parity flag, Auxiliary carry flag, Zero
flag, Overflow flag,
Trap flag, Interrupt flag, Direction flag, and Sign
flag.
Q7. What are the
various interrupts in 8086? Explain.
Ans. Maskable interrupts, Non-Maskable interrupts.
i) An interrupt that can be turned off by the
programmer is known as Maskable
interrupt.
ii) An interrupt which can be never be turned off
(ie.disabled) by the programmer
is known as Non-Maskable interrupt.
Q8. Which
interrupts are generally used for critical events?
Ans. Non-Maskable interrupts are used in critical events. Such
as Power failure, Emergency, Shut off etc.
Q9. What is the effect of executing
the instruction?
MOV CX, [SOURCE_MEM]
Where SOURCE_MEM equal to 2016 is a memory location offset relative to the current data segment
starting at address 1A00016
Ans. Execution of this instruction
results in the following:
((DS) 0 + 2016) à (CL)
((DS)
0 + 2016 + 116) à (CH)
In other
words, CL is loaded with the contents held at memory address
1A00016 +2016 +116 =1A02116
Q10. The original contents
of AX, BL, word-sized memory location SUM, and carry flag
CF are 1234H, ABH, 00CDH, and 0H,
respectively. Describe the results of
executing the following sequence of
instructions:
ADD
AX, [SUM]
ADC
BL, 05H
INC
WORD PTR [SUM]
Ans. Executing
the first instruction adds the word in the accumulator and the word in the
memory
location pointed to by address SUM. The result is placed in the
accumulator.
That is,
(AX)
← (AX) + (SUM) = 1234H + 00CDH = 1301H
The carry
flag remains reset.
The second instruction adds to
the lower byte of the base register (BL) the immediate operand 5H and the carry
flag, which is 0H. This gives
(BL)
← (BL) + imm8 + (CF) = ABH + 5H+ 0H = B0H
Since no carry is generated CF
remains reset.
The last instruction increments
the contents of memory location SUM by one. That is,
(SUM)
← (SUM) + 1H = 00CDH + 1H =00CEH
Q11. The 2’s
complement signed data contents of AL
equal -1 and the contents of CL are
-2. What result is produced in AX by
executing the following instructions:
i) MUL CL ii) IMUL CL
Ans. As binary
data, the contents of AL and CL are
(AL) = -1 (as 2’s
complement) = 111111112 = FFH
(CL)
= -2 (as 2’s complement) = 111111102 = FEH
Executing the
MUL instruction gives
(AX)
= 111111112 * 111111102 = 11111101000000102
= FD02H
The second
instruction multiplies the two numbers as signed numbers to generate
the signed
result. That is,
(AX)
= -1H * -2H
= 2H = 0002H
Q12. Explain different types of
registers in 8086 microprocessor arch.
Ans. Most of the registers
contain data/instruction offsets within 64 KB memory segment. There are four
different 64 KB segments for instructions, stack, data and extra data. To
specify where in 1 MB of processor memory these 4 segments are located the
processor uses four segment registers:
Code segment (CS) is a 16-bit register containing address of 64 KB
segment with processor instructions. The processor uses CS segment for all
accesses to instructions referenced by instruction pointer (IP) register. CS
register cannot be changed directly. The CS register is automatically updated
during far jump, far call and far return instructions.
Stack segment (SS) is a 16-bit register containing address of 64KB
segment with program stack. By default, the processor assumes that all data
referenced by the stack pointer (SP) and base pointer (BP) registers is located
in the stack segment. SS register can be changed directly using POP
instruction.
Data segment (DS) is a 16-bit register containing address of 64KB
segment with program data. By default, the processor assumes that all data
referenced by general registers (AX, BX, CX, DX) and index register (SI, DI) is
located in the data segment. DS register can be changed directly using POP and
LDS instructions.
Extra segment (ES) is a 16-bit register containing address of 64KB
segment, usually with program data. By default, the processor assumes that the
DI register references the ES segment in string manipulation instructions. ES
register can be changed directly using POP and LES instructions.
It is possible to change default segments used by general and index
registers by prefixing instructions with a CS, SS, DS or ES prefix.
All general registers of the 8086 microprocessor can be used for
arithmetic and logic operations. The general registers are:
Accumulator register consists of 2 8-bit registers AL and AH, which can be
combined together and used as a 16-bit register AX. AL in this case contains the low-order byte
of the word, and AH contains the high-order byte. Accumulator can be used for
I/O operations and string manipulation.
Base register consists of 2 8-bit registers BL and BH, which can
be combined together and used as a 16-bit register BX. BL in this case contains
the low-order byte of the word, and BH contains the high-order byte. BX
register usually contains a data pointer used for based, based indexed or
register indirect addressing.
Count register consists of 2 8-bit registers CL and CH, which can
be combined together and used as a 16-bit register CX. When combined, CL
register contains the low-order byte of the word, and CH contains the
high-order byte. Count register can be used as a counter in string manipulation
and shift/rotate instructions.
Data register consists of 2 8-bit registers DL and DH, which can
be combined together and used as a 16-bit register DX. When combined, DL
register contains the low-order byte of the word, and DH contains the
high-order byte. Data register can be used as a port number in I/O operations.
In integer 32-bit multiply and divide instruction the DX register contains
high-order word of the initial or resulting number.
The following registers are both general and index registers:
Stack Pointer (SP) is a 16-bit register pointing to program stack.
Base Pointer (BP) is a 16-bit register pointing to data in stack
segment. BP register is usually used for based, based indexed or register indirect
addressing.
Source Index (SI) is a 16-bit register. SI is used for indexed,
based indexed and register indirect addressing, as well as a source data
address in string manipulation instructions.
Destination Index (DI) is a 16-bit register. DI is used for
indexed, based indexed and register indirect addressing, as well as a
destination data address in string manipulation instructions.
