# 8051 Microcontroller Questions and Answers – Architecture

This set of 8051 Micro-controller Multiple Choice Questions & Answers (MCQs) focuses on “Architecture”.

1. How are the status of the carry, auxiliary carry and parity flag affected if the write instruction
MOV A,#9C
a) CY=0,AC=0,P=0
b) CY=1,AC=1,P=0
c) CY=0,AC=1,P=0
d) CY=1,AC=1,P=1

Explanation: On adding 9C and 64, a carry is generated from D3 and from the D7 bit so CY and AC are set to 1. In the result, the number of 1’s present are even so parity flag is set to zero.

2. How are the bits of the register PSW affected if we select Bank2 of 8051?
a) PSW.5=0 and PSW.4=1
b) PSW.2=0 and PSW.3=1
c) PSW.3=1 and PSW.4=1
d) PSW.3=0 and PSW.4=1

Explanation: Bits of PSW register are CY, AC, F0, RS1, RS0, OV, -, P so for selecting bank2 RS1=1 and RS0=0 which are fourth and third bit of the register respectively.

3. If we push data onto the stack then the stack pointer
a) increases with every push
b) decreases with every push
c) increases & decreases with every push
d) none of the mentioned

Explanation: If we push elements onto the stack then the stack pointer increases with every push of element.

4. On power up, the 8051 uses which RAM locations for register R0- R7
a) 00-2F
b) 00-07
c) 00-7F
d) 00-0F

Explanation: On power up register bank 0 is selected which has memory address from 00H-07H.

5. How many bytes of bit addressable memory is present in 8051 based microcontrollers?
a) 8 bytes
b) 32 bytes
c) 16 bytes
d) 128 bytes

Explanation: 8051 microcontrollers have 16 bytes of bit addressable memory.

6. 8051 microcontrollers are manufactured by which of the following companies?
a) Atmel
b) Philips
c) Intel
d) All of the mentioned

Explanation: 8051 microcontrollers are manufactured by Intel, Atmel, Philips/Signetics, Infineon, Dallas Semi/Maxim.

7. AT89C2051 has RAM of:
a) 128 bytes
b) 256 bytes
c) 64 bytes
d) 512 bytes

Explanation: It has 128 bytes of RAM in it.

8. 8051 series has how many 16 bit registers?
a) 2
b) 3
c) 1
d) 0

Explanation: It has two 16 bit registers DPTR and PC.

9. When 8051 wakes up then 0x00 is loaded to which register?
a) PSW
b) SP
c) PC
d) None of the mentioned

Explanation: When 8051 wakes up, Program Counter (PC) loaded with 0000H. Because of this in 8051 first opcode is stored in ROM address at 0000H.

10. When the microcontroller executes some arithmetic operations, then the flag bits of which register are affected?
a) PSW
b) SP
c) DPTR
d) PC

Explanation: It stands for program status word. It consists of carry, auxiliary carry, overflow, parity, register bank select bits etc which are affected during such operations.

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