2014-04-26 06:25 PM
The picture is the wave form of STM32F429 osc_out pin,The low level is not 0V, but is 1.24V, Why the sine wave's value of peak to peak is 1.04V. Is it correct?
2014-04-28 02:54 AM
Yes that is correct.
That voltage is needed to bias the osc_in pin so it operates as an amplifier rather than a digital inverter.Inside the stm32 there is a resistor that goes between osc_out and osc_in, perhaps 10 Megohms. So there is no DC voltage across the crystal.As well as this resistor to set the bias, there is also a mechanism to control the gain of this amplifier and thereby the amplitude of oscillations. This is so that you should be able to get reliable oscillations without consuming excessive power or damaging the crystal.Hope this helps,Danish2014-04-29 03:03 AM
Thank you for help.