Question

The output of the following 8051 Assembly code is: 

• A. A = 10
• B. [01] = 20
• C. [10] = 20
• D. [20] = 10

Hint:

In 8051 Assembly, indirect addressing with @R1 stores data in the memory location pointed by R1. If R1 = 01H, then MOV @R1, A stores A's value at memory[01H].

Answer 1

The Correct Option is B

Step 1: Analyzing each instruction: 1. MOV A, \#10 → Load immediate value 10H into Accumulator (A). \[ A = 10H \] 2. MOV 01H, A → Store the value of A (10H) into memory address 01H. \[ \text{Memory[01H]} = 10H \] 3. MOV A, \#20 → Load immediate value 20H into Accumulator (A). \[ A = 20H \] 4. MOV @R1, A → Store the value of A (20H) at the memory location pointed by Register R1. 
Step 2: The value of R1 is not explicitly initialized in the code, but if we assume R1 = 01H (default assumption in 8051), then: \[ \text{Memory[01H]} = 20H \] 
Step 3: Evaluating options: 
- (A) A = 10 (Incorrect): A is 20H at the end. 
- (B) [01] = 20 (Correct): Memory location 01H holds 20H.
- (C) [10] = 20 (Incorrect): Memory 10H was never modified. 
- (D) [20] = 10 (Incorrect): Memory 20H is not involved.