MCQs on Microprocessor


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01․ How can we make any bit of a register β€œ1”?
AND that bit with β€œ0” and remaining bits with β€œ1”.
AND that bit with β€œ1” and remaining bits with β€œ0”.
OR that bit with β€œ0” and remaining bits with β€œ1”.
OR that bit with β€œ1” and remaining bits with β€œ0”.

If we want to make any bit β€œ1”, then we have to OR that bit with β€œ1” so that the bit becomes β€œ1”. We also have to OR the remaining bits of the register with β€œ0” so that they remain unaltered.

02․ When RET instruction is executed by any subroutine then
the top of the stack will be popped out and assigned to the PC.
without any operation, the calling program would resume from instruction immediately following the call instruction.
the PC will be incremented after the execution of the instruction.
without any operation, the calling program would resume from instruction immediately following the call instruction and also the PC will be incremented after the execution of the instruction.

When RET instruction is executed by any subroutine then two bytes from the top of the stack will be popped out and assigned to the Program counter and the program execution begins at the new address.

03․ Which of the following instruction is not possible in 8085?
POP PSW
POP B
POP D
POP 30 H

POP 30 H instruction is not possible in 8085 because POP instruction is used with register pair or PSW. By using this instruction the content of the memory location pointed out by the stack pointer register are copied to the low order register. 30 H is not a valid register pair or memory address so this instruction is invalid

04․ How many T-states are required for execution of OUT 80H instruction?
10
13
16
7

OUT operation means Output data from Accumulator to a port with 8 bit address.The contents of the accumulator are copied into the output port.It is a two byte operation with 3 machine cycles and 10 T states.10T states 4 for Opcode fetch, 3 for Memory read and 3 for I/O write operation.

05․ How many machine cycles are required for execution of IN 30H instruction
3
4
5
6

IN instruction means Input data to Accumulator from a port with 8-bit address.IN 30H is a 2 byte instruction which requires 3 machine cycles i.e. Opcode fetch, read, read(operand read from the 8 bit port address).

06․ Length of the instruction POP D is
1 byte
2 byte
3 byte
4 byte

By POP instruction the contents of the memory location pointed out by the stack pointer register are copied to the low order register of the operand.POP D is an 1 byte instruction.

07․ While INX B instruction execute,
only carry flag will be affected
all flags will be affected
only carry and zero flags will be affected
no flags will be affected

The flags (flip flop) are affected by the arithmetical and logical operations in the ALU. Flags generally reflects the data conditions in the accumulator with some exception. INX B is a instruction which increment the content of the register pair BC by 1 and it does not affect any of the flags.

08․ While STC instruction executes,
only carry flag will be affected.
all flags will be affected.
only carry and zero flags will be affected.
no flags will be affected.

While STC instruction executes, microprocessor sets the carry flag to 1. So this instruction affects the carry flag only.

09․ While CMP B instruction executes,
only carry flag will be affected.
all flags will be affected.
only carry and zero flags will be affected.
no flags will be affected.

While CMP B instruction executes, microprocessor compares the contents of register B with the contents of the accumulator. The comparison is shown by setting all the flags. The flags S, P, AC are modified and flag Z and CY reflects the result of the operation. So, all flags will be affected.

10․ Which instruction is required to rotate the content of accumulator one bit right along with carry?
RLC
RAL
RRC
RAR

RAR instruction means rotate accumulator right through carry. By this instruction each bit of the accumulator is rotated right by one position through the carry flag. The carry flag is set by the least significant digit and content of the carry flag is placed in the most significant position. Example : accumulator contents before instruction is 10100111 and the flag is set by 0. After the instruction executes the accumulator content is 01010011 and the flag is set by 1.

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