Should LSERDY assert with LSEBYP?

Uwe Bonnes · ‎2019-04-23

Hello,

should LSERDY assert with LSEBYP?

I have a SIT1533 (32.768 khz Mems ocsillator) connected to PC14/OSC32IN on a L412. I first reset the backup domain, than I enable LSEBYP and with next command I enable LSEON. On a cold start, where the SIT1533 may need 500 ms, LSERDY never asserts, also OSCIN is toggling when I check with a scope.

Otherwise why does the sequence

reset BCDR
wait that LSERDY is de-asserted
set LSEBYP
wait untill LSEBY is asserted
set LSEON
wait until LSEON is asserted
apply clk to OSC32 in

not set LSERDY?

Vangelis Fortounas · ‎2019-04-23

Hello.

LSERDY indicates crystal's oscillation stability.

I didn't found any mentioned relationship between these two bits, but also is not mentioned the state of LSERDY in case of using external osc. (probably undefined)