8051 loop behavior with port polling Program fragment: STAT: MOV A, P0 MOV P2, A JNB P2.3, STAT This code reads Port 0 to A, writes A to Port 2, and will stop looping when bit 3 of Port 2 becomes set. Choose the correct statement.

Introduction / Context:
Polling a port bit with conditional jumps is a common technique on the 8051. Understanding the meaning of JNB, which stands for Jump if Not Bit, is essential for predicting control flow. This fragment mirrors a simple data transfer from Port 0 to Port 2 followed by a loop controlled by a single bit on Port 2.

Given Data / Assumptions:

• MOV A, P0 copies the current Port 0 value into A.
• MOV P2, A outputs the accumulator value to Port 2 latch.
• JNB P2.3, STAT jumps back to STAT only if bit 3 of Port 2 is 0.

Concept / Approach:

JNB tests the specified bit, and if that bit equals 0, program control branches to the label. If the bit equals 1, the branch is not taken and execution falls through, thereby exiting the loop. The code therefore continues looping while P2.3 remains 0 and stops looping when P2.3 becomes 1.

Step-by-Step Solution:

Verification / Alternative check:

Simulate with different input patterns or manually set P2.3 through hardware. Observe that the loop persists while P2.3 is 0 and stops when P2.3 goes to 1.

Why Other Options Are Wrong:

False: contradicts JNB behavior.

Loops until P2.3 becomes 0: it already loops when 0; termination occurs when it becomes 1.

Never terminates: false if hardware or program logic can set P2.3 to 1.

Common Pitfalls:

Confusing JNB with JB, and assuming port pins always reflect latch writes even when configured as inputs with external pullups. Real hardware behavior depends on wiring and port mode.

Final Answer:

True