250+ TOP MCQs on I/O Port Programming and Addressing Modes

8051 Micro-controller Multiple Choice Questions on “I/O Port Programming and Addressing Modes”.

1. To initialize any port as an output port what value is to be given to it?
a) 0xFF
b) 0x00
c) 0x01
d) A port is by default an output port

Answer: d
Clarification: In 8051, a port is initialized by default in its output mode no need to pass any value to it.

2. Which out of the four ports of 8051 needs a pull-up resistor for using it is as an input or an output port?
a) PORT 0
b) PORT 1
c) PORT 2
d) PORT 3

Answer: a
Clarification: These pins are the open drain pins of the controller which means it needs a pull-up resistor for using it as an input or an output ports.

3. Which of the ports act as the 16 bit address lines for transferring data through it?
a) PORT 0 and PORT 1
b) PORT 1 and PORT 2
c) PORT 0 and PORT 2
d) PORT 1 and PORT 3

Answer: c
Clarification: PORT 0 and PORT 2 are used as the 16 bit address lines where PORT0 act as lower bit address lines and PORT 2 as higher bit address lines.

4. Which of the following registers are not bit addressable?
a) SCON
b) PCON
c) A
d) PSW

Answer: b
Clarification: PCON register is not a bit addressable register.

5. Which instruction is used to check the status of a single bit?
a) MOV A,P0
b) ADD A,#05H
c) JNB PO.0, label
d) CLR P0.05H

Answer: c
Clarification: JNB which stands for Jump if no bit checks the status of the bit P0.0 and jumps if the bit is 0.

6. Which addressing mode is used in pushing or popping any element on or from the stack?
a) immediate
b) direct
c) indirect
d) register

Answer: b
Clarification: If we want to push or pop any element on or from the stack then direct addressing mode has to be used in it, as the other way is not accepted.

7. Which operator is the most important while assigning any instruction as register indirect instruction?
a) $
b) #
c) @
d) &

Answer: c
Clarification: In register, indirect mode data is copied at that location where R0 or R1 are present, so @ operator is used ex. MOV @R0,A

8. What is the advantage of register indirect addressing mode?
a) it makes use of registers R0 and R1
b) it uses the data dynamically
c) it makes use of operator @
d) it is easy

Answer: b
Clarification: Register indirect addressing mode is useful if a series of data is to be assigned to that address, with the help of this quality the number of instructions decreases as a result of which performance increases.

9. Which of the following comes under the indexed addressing mode?
a) MOVX A, @DPTR
b) MOVC @A+DPTR,A
c) MOV A,R0
d) MOV @R0,A

Answer: b
Clarification: Indexed addressing mode stands for that instruction where the bits of the accumulator is also indexed with the 16 bit registers.

10. Is this a valid statement?
SETB A
a) yes
b) no
c) cant be determined
d) none of the mentioned

Answer: b
Clarification: SETB is used to set a bit of a register. A stands for accumulator which is an 8 bit register, so it is an invalid instruction.