Temperature Monitor: PB3/PB4 Conflict with JTAG
Finds unresponsive STM32F103 key inputs by checking debug-port pin multiplexing.
Project: STM32F103 Dual-Channel Temperature Monitoring and Alarm System
Symptom: Key inputs on PB3/PB4 did not behave as GPIO.
Hypothesis: Check wiring and debounce first, then determine whether alternate debug functions still own the pins.
Investigation: Brought up MCU, sensors, OLED, alarm, keys, SD and UART in order and checked debug-port multiplexing.
Root cause: PB3/PB4 were still assigned to the full JTAG interface.
Fix: Disabled full JTAG while retaining SWD, then re-tested keys and retained SD state plus error counters for later diagnosis.
Lesson: Check pin multiplexing before rewriting application logic. The project and flashable HEX exist; sensor voltage, SD and alarm behavior still require board verification.