STM32L151 clock issue

[chaitanya jasti]

Posted on May 01, 2017 at 09:11

Hi,

i am using STM32L151 in our borad and for main clock source i have used pericom 8mHZ crstal and when i am trying to observe clock on scope ,i am unable see the clock.But SW team programmed the controller and with LED blinking and it is working fine on one of the GPIO.

Can any one confirm is my external crystal is fine or the programmer used internal crystal to program.

Regards

chaitanya

[S.Ma]

Posted on May 01, 2017 at 12:13

If on a scope there is no oscillation, it means the HSI is most likely used, maybe since the reset release event. Also make sure the crystal is on the hse related pads and not mistakenly connected to a 32khz lse pads which could explain this situation. Otherwise, in debug mode look at the sys and rcc hw registers. Manipulate them until hse is working... 

[Tesla DeLorean]

Posted on May 01, 2017 at 16:33

You should use the MCO (PA8) pin to expose the clock as seen internally, probing the external crystal directly tends to alter its characteristics and is not reflective of normal operation. There is an App Note on crystal selection and component values for the STM32, please review.