Is OSC_IN actually the output and OSC_OUT the input on STM32F030?
Can someone tell me if I’m understanding this correctly?
In the documentation for the STM32F030R8T6 chip, specifically the "RM0360 Reference Manual", there’s a diagram showing how to connect an external crystal oscillator ("Figure 12. HSE/LSE clock sources"). In this diagram, the crystal is connected directly to the OSC_IN and OSC_OUT pins, with no series resistor on the OSC_OUT line to limit the drive level.
However, on the STM32F030 DISCOVERY board, there is such a resistor – R22 – even though the crystal is not installed by default. I added the crystal I wanted to use and measured the current through it (using a current clamp), and it became clear that it was being driven beyond its specified power limits. That’s when I realized the need for the series resistor (R22). I calculated the appropriate resistance value and installed it – but it didn’t reduce the current through the crystal at all.
After further investigation, I discovered that the OSC_OUT pin on the microcontroller is actually a high-impedance input, while OSC_IN is the output. So I tried placing the resistor in series with OSC_IN instead – and, as expected, this reduced the power dissipated in the crystal.
Is my understanding correct? And if so, does that mean the diagram in the official documentation is actually incorrect?
