How many fluctuations in the crystal oscillator will trigger the S9S12G128 reset?

jingfang · ‎09-14-2023

We have a crest in the crystal oscillator, and the mcu reset pin pulls down.

Is there a specification and timing ?

lama · ‎09-18-2023

Hi,
I'm not quite sure I understand your question.
If you read the document then you saw that the reset is clocked fro internal RC oscillator with the fvcorst frequency which can be within interval 8MHz~25MHz (for S12G device). It gives for worst case scenario (highest frequency) really tough conditions for capacitor setup. A lot of customers put 100nF at the reset pin to filter glitches but in this case they were never able to recognize COP. Usually 10nF capacitor is maximum.
The external crystal does not play any role during reset. The MCU always starts with internal oscillator to PEI mode. You are responsible to switch to the external oscillator after reset and enter the MCU into PBE or PEE mode.
The examples of different modes can be found here:
https://community.nxp.com/t5/S12-MagniV-Microcontrollers/S12G-Examples-Pack/ta-p/1103919

Best regards,
Ladislav

lama · ‎09-14-2023

Hi,

There is a picture Figure 10-34. RESET Timing in the reference manual which shows how the MCU recognizes reset source by number of fvcorst cycles till the reset source is released. (the figures can be also found at bellow mentioned site)

Probably some info about reset recognition which can help you is here to be able to correctly calculate R-C at reset pin to be COP correctly recognized… (note; in this family there are different reset vectors for some of reset sources)

https://community.nxp.com/t5/S12-MagniV-Microcontrollers/S12-FAMILY-DEVICES-COP-RECOGNITION-CONSIDER...

Best regards,

Ladislav

jingfang · ‎09-17-2023

Thank's a lot~

It seems to be how long it takes for the MCU reset pin to be pulled down to trigger the watchdog.

I also want to know: influence of crystal vibration on reset pin.

For example, how much the cyrstal vibration ampiltude is , the reset pin will be low or the crystale does not work, how long the reset pin will be low?