topic Re: MC56F8355 start-up in Digital Signal Controllers

MC56F8355 start-up

christophe_c — Fri, 19 Mar 2021 10:51:27 GMT

Hello, I have an issue about MC56F8355 start-up: - the internal voltage is equal to 2,5V and stable - the external Reset rises up after 173ms - the external clock is a cristal at 8Mhz and the amplitude signal is about 2V - the RSTO output rises up 20µs after Reset The DSC can start-up a few times but not at each time When the DSC doesn't start-up, the CLKO output is low Could you help me ? Thank you in advanced Regards Christophe

Re: MC56F8355 start-up

xiangjun_rong — Mon, 22 Mar 2021 01:30:00 GMT

Hi, Christophe,

It appears that the crystal works unreliably, pls refer to the configuration I copied from Data sheet:

From software, you have to set the OCCS_OSCTL[COHL]=1.

Pls add two caps on the EXTAL/XTAL pins and have a try. If you still have question, pls change another 8MHz crystal from different manufacturer.

Hope it can help you

XiangJun Rong

Re: MC56F8355 start-up

christophe_c — Wed, 14 Apr 2021 12:54:10 GMT

Hello,

I tried different crystal manufacturers, I tried a ceramic resonator and I applyed an external clock but the result is the same

I found a new information :

If I put a delay of 100ms between VddIO and Vdda_ADC, the DSC starts-up.

The VddIO has to apply after Vdda_ADC of the DSC.

Have you an explanation about that ?

Re: MC56F8355 start-up

xiangjun_rong — Thu, 15 Apr 2021 02:21:30 GMT

Hi,

Generally, you can use digital 3.3V(connected to VDDIO) to generate analog 3.3V(connected to VDDA) via a ferrite bead, while, you can connect a ferrite bead between VSS and VSSA.

I have checked the data sheet of MC56F8355, I have not seen the power-up sequence requirement for VDDIO and VDDA.

Xiangjun Rong