Can not detect specific LF carrier pattern wake up FXTH87xx?

[tedwu1]

Hi, 

The TPMS project used FXTH87xx. It was waked up by LF and its pattern is 1200mS on (has LF) and 50mS off (hasn’t LF). Now, I setup LF Receiver to detect 1024mS, it can detect the LF (about 1 second by LFCTRLA). Then I need to detect 50mS off (LF). But I cannot detect 50mS (carrier off) correctly. Do you know what’s wrong I am? Please do me a favor? Please see the attach file for detail. Why the LFDO is low at carrier? Code snippet at code.c.

Thank you very much.

[TomasVaverka]

Hi Ted,

I believe that you have already received a direct answer and access to a demo project from Camille.

The LF block was not designed so the LFDO bit can follow durations of several hundreds milliseconds, so a workaround is necessary to make it work. A possibility is to briefly turn off the LF block during the reception of the long ON pattern, in order to “reset” it and allow the LFDO bit to continue monitoring the signal.

Best regards,

Tomas