Short Question And Answer Microprocessor Set-2

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1. List the control and status signals available in 8085 ?.
ALE , RD, WR, IO/M, S1, S2
ALE-Address Latch Enable
RD – Read Control Signal
WR – Write Control Signal
IO/M – To specify I/O or memory operation
S1 , S2 – Status signals

2. 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.

3. 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.

4. 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

5. 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 .

6. Define Direct Addressing mode 😕
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.

7.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

8. List the branch related addressing mode:?

  • Intra segment Direct
  • Intra segment Indirect
  • Inter segment Direct
  • Inter Segment Indirect

9. List the functions of Bus Interface Unit in 8086.?

  • Sends out addresses
  • Fetches instructions from memory
  • Reads data from ports and memory
  • Writes data to port and memory

10. Write any two advantages of segment registers in 8086?
a. It allows the memory capacity to be 1MB even though the address associated with individual instructions are 16 bits wide.
b.It allows the instruction,data, or stack portion of a program to be more than 64KB long by using more than one code, data, or stack segment

11. 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.

12. 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.

13.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.

14.Define Register addressing mode:?

Datum is in the register that is specified by the instruction
E.g : MOV CX,AX (16bitoperand)
MOVCL,AL(8bitoperand)

15. 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.

16. 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.

17. 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.

18. 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.

19. 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.

20. 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.