topic Re: crystal selection in Digital Signal Controllers

crystal selection

MikeC1 — Wed, 14 Sep 2022 23:05:20 GMT

what is the absolute negative resistance value (Rs) for DSP56F803?

Need the value to select 8Mhz crystal oscillator, without load caps

Re: crystal selection

xiangjun_rong — Thu, 15 Sep 2022 07:51:51 GMT

Hi,

Pls refer to the fig for the external crystal connection without capacitor load.

I attach the user manual of DSP56F803-EVK, I copy the fig from the user manual of DSP56F803-EVK at page A-3.

Hope it can help you

XiangJun Rong

Re: crystal selection

MikeC1 — Thu, 15 Sep 2022 15:03:52 GMT

Thanks for responding

The info you provided me shows connectors in series with crystal and DSP on a development board, does not show driver circuit inside the DSP56F803. I need to know what the absolute negative resistance value (Rn) for DSP56F803? Need this value to select an alternative 8Mhz crystal oscillator with ESR=100, without load caps. Need to verify Rn is at least 500 ohms because the ESR need to be 1/5 of Rn. Attached below shows a method to find Rn. Do you have any test data values for Max ESR or Max Rn you can recommend for the DSP56F803?

Rx needs to be an RF SMD type pot. and soldered in series very close to the processor

The NXT/Freescale/Motorola Semi datasheets and manuals for this DSP56F803 do not mention or recommend an ESR or Rn value.

We are using the crystal in application shown below

Re: crystal selection

xiangjun_rong — Fri, 16 Sep 2022 02:50:19 GMT

Hi, Mike,

Unfortunately, I have checked all the data sheet and the other file, I did not find the negative resistor spec for the crystal circuit.

I am sorry.

XiangJun Rong