Question

Consider the following instruction sequence where registers \( R1 \), \( R2 \), and \( R3 \) are general purpose and MEMORY[X] denotes the content at the memory location \( X \): 
\[\begin{array}{|l|l|c|} \hline \textbf{Instruction} & \textbf{Semantics} & \textbf{Instruction Size (bytes)} \\ \hline \text{MOV R1, (5000)} & \text{\( R1 \leftarrow \text{MEMORY}[5000] \)} & \text{4} \\ \hline \text{MOV R2, (R3)} & \text{\( R2 \leftarrow \text{MEMORY}[R3] \)} & \text{4} \\ \hline \text{ADD R2, R1} & \text{\( R2 \leftarrow R1 + R2 \)} & \text{2} \\ \hline \text{MOV (R3), R2} & \text{\( \text{MEMORY}[R3] \leftarrow R2 \)} & \text{4} \\ \hline \text{INC R3} & \text{\( R3 \leftarrow R3 + 1 \)} & \text{2} \\ \hline \text{DEC R1} & \text{\( R1 \leftarrow R1 - 1 \)} & \text{2} \\ \hline \text{BNZ 1004} & \text{Branch if not zero to the given absolute address} & \text{2} \\ \hline \text{HALT} & \text{Stop} & \text{1} \\ \hline \end{array}\]Assume that the content of memory location 5000 is 10, and the content of register \( R3 \) is 3000. The content of each of the memory locations from 3000 to 3010 is 50. The instruction sequence starts from memory location 1000. All numbers are in decimal format and the memory is byte addressable. 
After the execution of the program, the content of memory location 3010 is \(\underline{\hspace{2cm}}\).

Hint:

Always track loop bounds carefully to determine exactly which memory locations are updated.

Answer 1

Correct Answer: 50

Step 1: Initialization.
From the first instruction: \[ R1 = \text{MEMORY}[5000] = 10 \] Also given: \[ R3 = 3000 \] Memory locations from 3000 to 3010 are initially set to 50.

Step 2: Loop control. 
The instruction BNZ 1004 causes control to branch back as long as \( R1 \neq 0 \). Since \( R1 \) starts at 10 and is decremented by 1 in each iteration, the loop executes exactly 10 times.

Step 3: Effect of one loop iteration.
In each iteration, the following actions occur:

• The value at MEMORY[R3] is loaded into R2
• R1 is added to R2
• The result is written back to MEMORY[R3]
• R3 is incremented by 1
• R1 is decremented by 1

Thus, during the 10 iterations, the memory locations updated are: \[ 3000, 3001, \ldots, 3009 \]

 

Step 4: Observation about MEMORY[3010].
The loop modifies only the first 10 consecutive locations starting from address 3000. The address 3010 lies outside this range and is therefore never accessed or modified by the loop.

Step 5: Final value.
Since MEMORY[3010] was initially 50 and remains unchanged: \[ \text{MEMORY}[3010] = 50 \]

Final Answer:
\[ \boxed{50} \]