1. Why is the data bus bi-directional?
The data bus is bi-directional because the data flow in both directions Between the MPU and memory and peripheral devices.
2. How many memory locations can be addressed by a microprocessor with 14 address lines?
The 8085 MPU with its 14-bit address is capable of addressing 2 14 =16,384
(ie) 16K memory locations.
3. What is the function of the accumulator?
The accumulator is the register used to store the 8-bit data to perform the Arithmetic and logical operations.
4. Why are the program counter and the stack pointer 16-bit registers?
Memory locations for the program counter and stack pointer have 16-dit Address. So the PC and SP have
16-bit registers.
5. If the 8085 adds 87H and 79H, specify the contents of the accumulator and the
Status of the S, Z, and CY flag?
The sum of 87H and 79H=100H. Therefore, the accumulator will have 00H, and the flags will be S=0, Z=1,
CY=1.
6. Write down the control and status signals?
Two control signals and three status signals
Control signals: RD and WR
Status signals: IO/M, S1, S2
7. Define instruction cycle, machine cycle and T-state.
Instruction cycle is defined, as the time required completing the execution of the instruction
(combination of 1-5 machine cycles).
Machine cycle is defined, as the time required completing one operation of accessing memory and I/O.
(collection of 3-6 T-state).
1 clock pulse is called as 1 T-state.

8. Give the functional categories of 8085 micro instructions? o Data transfer operations o Arithmetic operations o Logical operations o Branching operations o Machine control operations
9. Define Opcode and operand?
The operation to be performed is called Ocode.
The data to be operated is Called operand.
10. Define two-byte instruction with one example?
In a 2-byte instruction, the first byte specifies the Opcode; the second byte specifies the operand.
Example: Opcode operand
MVI A, Data
7. What operation can be performed by using the instruction ADD A?
The instruction ADD a will add the content of the accumulator to itself;
This is equivalent to multiplying by 2.
8. What is data transfer instructions?
The data transfer instructions copy data from one source in to a destination without modifying the content of the source.
9. Define a program?
A program is a sequence of instructions written to tell the computer to perform a specific function.
10. Give the difference between JZ and JNZ?
JZ change the program sequence to the location specified by the 16-bit address if the zero flag is set

JNZ change the program sequence to the location specified by the 16-bit address if the zero flag is reset.
11. What is the machine control operations used in 8085 microprocessor?
HLT: Halt
NOP: No Operation
12. What are the types of rotate instructions?
RLC = Rotate Accumulator Left
RRC=Rotate Accumulator Right
RAL =Rotate Accumulator Left through Carry
RAR =Rotate Accumulator Right through Carry
14. Why address bus is unidirectional?
Address bus is unidirectional as address is generated by microprocessor and it is provided to i/o devices as well as memory when a read and write operation is done.
15. What is Microprocessor? Give the power
supply & clock frequency of 8085?
Ans: A microprocessor is a multipurpose, programmable, register based, clock driven electronic device that reads binary instructions from memory accepts binary data as input and processes data according to those instructions and provides result as output.
The power supply of 8085 is +5V and clock frequency in 3MHz.
16. List the 16 – bit registers of 8085 microprocessor
Ans: Stack pointer (SP) and
Program counter (PC).
List the allowed register pairs of 8085.
Ans:
 B-C register pair
 D-E register pair
 H-L register pair
17. What is the function of IO/M signal in the 8085?

Ans: It is a status signal. It is used to differentiate between memory locations and I/O operations. When this signal is low (IO/M = 0) it denotes the memory related operations. When this signal is high (IO/M = 1) it denotes an I/O operation.
18. List the four instructions which control the interrupt structure of the 8085
microprocessor.
Ans:
 DI ( Disable Interrupts )
 EI ( Enable Interrupts )
 RIM ( Read Interrupt Masks )
 SIM ( Set Interrupt Masks )
19. Chose the correct of the following
1. The 8085 can address a) 256-Bytes b) 16K-Bytes c) 32K –Bytes d) 64K-Bytes
2. The 1 St cycle of every machine cycle of 8085 is a a) Fetch cycle b) Execute cycle c) Fetch and execute both d) None
3. Which type of addressing mode is used in CMP R instruction? a) Direct b) Implied c) Register d) Indirect
4. Which register keeps track of program during execution a) Data register b) Program counter c) Instruction reg. d) None of these
5. During fetch cycle the microprocessor fetches the opcode and operand a) From I/O devices b) from memory c) from both d) None of these
6. The data width of 8085 is a) 4-bits b) 8-bits c) 16-bits d) 32-bits
7. Time required to execute an instruction is called a) T-state b) Machine cycle c) Instruction cycle d) none of these
20. How many address line does 4 Kbytes memory chip need?
4KB=4*1KB=2 2 * 2 10 B=2 12 B (Bcoz 2 10 B=1KB)

So, No of address lines are required is 12.
21.
Write instructions for these.
(i) (C)  (B)
(ii) (A)  (2000h)
(iii) (A)  (A) – 35h
(iv) (A)  (A)’
(v) (C)  (C) -1 vi) (E)  (E) + 1
(vii) (HL) <--(HL) +(DE)
Ans: (i).MOV C, B (ii). LDA 2000H (iii). SUI 35h (iv) CMA (v). DCR C (vi). INR E (vii). DAD D
22.
Assuming content of Registers A and B equal to 55h and 57h respectively,
Find their content on execution of following in each case separately.
(i)MOV B,A (ii) INR A (iii) SUB A (iv) CMP B (v) RAL (vi) ANI F0h (vii) SUB B
Ans: (i).A=55H, B=55H (ii).A=56H, B=57H (iii). A=00H, B=57H (iv).A=55H, B=57H
(v).A=AA H, B=57H (vi).A=50H, B=57H (vii). A=F6H, B=57H