8085 Microprocessor

1. The  Program counter in a 8085 microprocessor is a 16-bit register, because

Ans  : There are 16 address lines. 8085 has 16-bit address bus

2. In Intel 8085A microprocessor ALE signal is made high to

Ans : Enable the data bus to be used as low order address bus

ALE stands for Address Latch Enable. It is the 3oth pin of 8085 which is used to enable or disable the address bus. the address bus will be enabled during the 1st clock cycle as the ALE pin goes high i.,e logic '1' during the first half cycle

3. In 8085, which of the following modifies the program counter?

Ans : All instructions (PCHL, ADD, JMP & CALL)

4. If CS=A₁₅’A₁₄A₁₃ is used as the chip select of a 4K RAM in an 8085 system, then its memory  range will be 

Ans: 6000H - 6FFFH and 7000H - 7FFFH 

5. The contents of a register (B) and Accumulator (A) of 8085 microprocessor are 49H and 3AH respectively. The contents of A and the status of carry flag (CY) and sign flag (S) after executing SUB B instruction are 

Ans : A=F1,  CY=1,   S=1

6. Which block within a microprocessor performs the integer arithmetic and bit-wise logical operations?

Ans : Arithmetic Logic Unit

7. An 8 Kbyte ROM with an active low chip select input CS is to be used in an 8085 microprocessor based system . The ROM should occupy the address range 1000H to 2FFFH. The address lines are designated as A15 to A0, where as A15 is the most significant address bit. One of the following logic expression will generate the correct CS signal for this ROM ?

Ans  : A₁₅ + A₁₄ + A₁₃A₁₂ + A₁₃’A₁₂  

8. The clock frequency of an 8085 microprocessor is 5 MHZ. If the time required to execute an instruction is 1.4µs, then the number of T-states needed for executing the instruction is 

Ans :  7

As Clock Frequency = 5 MHZ , time period (1/f) = 0.2µs, therefore for 0.2µs X 7 = 1.4µs

9. The following five instructions were executed on an 8085 microprocessor.

MVI A, 25H

MVI B, 91H

ADD B

CMA

ANI 68H

The accumulator value immediately after the execution of the fifth instruction is 

Ans : 48H

10. An 8085 assembly language program is given below. Assume that the carry flag is initially unset. The content of the accumulator after the execution of the program is

MVI A,07H

RLC

MOV B,A

RAL

RLC

ADD B

RRC

Ans : 23H

11. After the execution of the instruction XRA A the contents of A , carry and zero flags are respectively

Ans : A=00, CY=0, Z=1

As XRA is Exclusive OR operation, it will result as zero. The XRA A instruction is used to clear the contents of the Accumulator and store the value 00H.

12.  An RRC instruction in 8085 microprocessor instruction set will affect 

Ans : Carry Flag 

In 8085 Instruction set, RRC stands for “Rotate Right Accumulator”.  In this right rotation, the least significant bit will come out from the Accumulator and will be copied to CY bit in the flag register and also will be copied to the most significant bit position of the Accumulator.

13. What is the difference between MOV and MVI instructions of an 8085 microprocessor?

Ans : MOV instruction copies data between two registers, where as MVI instruction transfers an immediate data into a register.

14. In 8085 addition which of the following flags are set  when the addition of MSBs is more than 10?

Ans : Carry flag

15. The following instruction indicates which types of addressing mode?

LDAX B

Ans : Indirect address mode

LDAX stands for LoaD Accumulator indirect from register pair (X), and again by the name, you can tell that it uses indirect addressing.