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Electronics Engineering QUESTION #11700
Question 1
A microcontroller's GPIO pin configured as output is stuck LOW despite the firmware commanding it HIGH. After confirming the code is correct, the most likely hardware cause is:
  • The pin's pull-up resistor is too large
  • An external device is shorting the pin to GND (bus contention)✔️
  • The supply voltage $V_{CC}$ is too high
  • The crystal oscillator frequency is incorrect
Correct Answer Explanation
Bus contention occurs when an external device (or another GPIO configured as output-low) drives the pin LOW while the MCU drives it HIGH. The resulting short-circuit current clamps the pin LOW and can permanently damage both devices. The fix is to add a series resistor or reconfigure the conflicting driver.