Question 1 |

The content of the registers are R_{1} = 25H, R_{2} = 30H and R_{3} = 40H. The following machine instructions are executed.

\text{PUSH } \{R_{1}\}

\text{PUSH } \{R_{2}\}

\text{PUSH } \{R_{3}\}

\text{POP } \{R_{1}\}

\text{POP } \{R_{2}\}

\text{POP } \{R_{3}\}

After execution, the content of registers R_{1},\:R_{2},\:R_{3} are

\text{PUSH } \{R_{1}\}

\text{PUSH } \{R_{2}\}

\text{PUSH } \{R_{3}\}

\text{POP } \{R_{1}\}

\text{POP } \{R_{2}\}

\text{POP } \{R_{3}\}

After execution, the content of registers R_{1},\:R_{2},\:R_{3} are

R_{1}=40H,\:R_{2}=30H,\:R_{3}=25H | |

R_{1}=25H,\:R_{2}=30H,\:R_{3}=40H | |

R_{1}=30H,\:R_{2}=40H,\:R_{3}=25H | |

R_{1}=40H,\:R_{2}=25H,\:R_{3}=30H |

Question 1 Explanation:

For PUSH SP is decremented and for POP SP is incremented.

\begin{aligned} \therefore \qquad [\mathrm{R} 1]&=40 \\ [\mathrm{R} 2]&=30 \\ [\mathrm{R} 3]&=25 \end{aligned}

\begin{aligned} \therefore \qquad [\mathrm{R} 1]&=40 \\ [\mathrm{R} 2]&=30 \\ [\mathrm{R} 3]&=25 \end{aligned}

Question 2 |

The clock frequency of an 8085 microprocessor is 5 MHz. If the time required to execute an instruction is 1.4 \mu s, then the number of T-states needed for executing the instruction is

1 | |

6 | |

7 | |

8 |

Question 2 Explanation:

Given than,

f_{\mathrm{CLK}}=5 \mathrm{MHz}

Execution time =1.4 \mu \mathrm{s}

Execution time =n(T-\text { state })

n= number of T-states required to execute the instruction

T- state (or) T_{\mathrm{CLK}}=\frac{1}{f_{\mathrm{CLK}}}=0.2 \mu \mathrm{s}

So, \quad n=\frac{1.4 \mu \mathrm{s}}{T_{\mathrm{CLK}}}=\frac{1.4}{0.2}=7

f_{\mathrm{CLK}}=5 \mathrm{MHz}

Execution time =1.4 \mu \mathrm{s}

Execution time =n(T-\text { state })

n= number of T-states required to execute the instruction

T- state (or) T_{\mathrm{CLK}}=\frac{1}{f_{\mathrm{CLK}}}=0.2 \mu \mathrm{s}

So, \quad n=\frac{1.4 \mu \mathrm{s}}{T_{\mathrm{CLK}}}=\frac{1.4}{0.2}=7

Question 3 |

In an 8085 microprocessor, the contents of the accumulator and the carry flag are A7 (in hex) and 0, respectively. If the instruction RLC is executed, then the contents of the accumulator (in hex) and the carry flag, respectively, will be

4E and 0 | |

4E and 1 | |

4F and 0 | |

4F and 1 |

Question 3 Explanation:

RLC: Rotate accumulator left by 1 bit without carry

Before RLC operation:

\begin{aligned} A &=A 7 H=(10100111)_{2} \\ C Y &=0 \end{aligned}

After RLC operation:

\begin{aligned} A &=(01001111)_{2}=4 \mathrm{FH} \\ \mathrm{CY} &=1 \end{aligned}

Before RLC operation:

\begin{aligned} A &=A 7 H=(10100111)_{2} \\ C Y &=0 \end{aligned}

After RLC operation:

\begin{aligned} A &=(01001111)_{2}=4 \mathrm{FH} \\ \mathrm{CY} &=1 \end{aligned}

Question 4 |

In an 8085 system, a PUSH operation requires more clock cycles than a POP operation. Which one of the following options is the correct reason for this?

For POP, the data transceivers remain in the same direction as for instruction fetch (memory to processor), whereas for PUSH their direction B174has to be reversed. | |

Memory write operations are slower than memory read operations in an 8085 based system. | |

The stack pointer needs to be pre-decremented before writing registers in a PUSH, whereas a POP operation uses the address already in the stack pointer. | |

Order of registers has to be interchanged for a PUSH operation, whereas POP uses their natural order. |

Question 4 Explanation:

The stack pointer needs to be pre-decremented
before wiriting data into stack. For reading data
from stack, such pre-decrement or pre-increment
operations are not needed, as already stack
pointer indicates the address of stack top from
where the read operation takes place.
Hence, PUSH operation requires more clock
cycles than POP operation.

Question 5 |

In an 8085 microprocessor, which one of the following instructions changes the content of the accumulator?

MOV B,M | |

PCHL | |

RNZ | |

SBI BEH |

Question 5 Explanation:

The only instruction that changes the contents of
accumulator is SBI BEH.

There are 5 questions to complete.