I ported this library from GitHub to my STM32. I understand quite well what it does, and the default configuration seems to make sense. However, when I send the transceive command, the antenna output turns on DC instead of AC 13.7 MHz. There seems to be a problem with the modulation. Also, it stops replying to I2C messages from my STM32.
I checked the quarz, it runs with 27 MHz as it sould. So I guess it is a configuration problem. To me it sounds like the TxSel bits in the TxCon register control the modulation, but none of the values worked as expected.
Thanks for your suggestions.