I'm intending to use PC13 as an output to drive the onboard LED, but at some point in my program the PC13 pin begins outputting a 4.4 khz signal with pulse width that varies from 0% to 100% back to 0% and keeps repeating that pattern at approx 4 Hz. Is this caused by the RTC calibration function? How can I turn it off. I didn't intentionally turn it on.
