PIC with external crystal alone is OK?

[cupoftea]

Hi,
If this 8MHz crystal (CSTNE8M00G55A000R0) is used as an external oscillator for the PIC24FJ1024GB610-I/PT microcontroller, then will it really not need any external resistors whatsoever to be used with it?

CSTNE8M00G55A000R0
https://www.murata.com/en-eu/products/productdetail?partno=CSTNE8M00G55A000R0

PIC24FJ1024GB610-I/PT

https://ww1.microchip.com/downloads/en/DeviceDoc/PIC24FJ1024GA610-GB610-Family-Data-Sheet-DS30010074G.pdf

 

[betwixt]

No external resistors or capacitors are needed as long as the ground connection is connected with low impedance to the VSS pin.

Brian.

 

[KlausST]

Hi,

The datasheet shows a typical application circuit ... with additional parts Rd and Rf..

Klaus

 

[cupoftea]

Thanks yes the page 6 does show 2 resistors, but im not sure if they pertain to the PIC24FJ1024GB610-I/PT crystal input.?
Also , crystal outputs are weak, so i am surprised they have a series 330R with it.

CSTNE8M00G55A000R0 crystal datasheet

https://www.murata.com/products/productdata/8801161674782/SPEC-CSTNE8M00G55A000R0.pdf?1559743212000

 

[KlausST]

^page 6 does show 2 resistors, but im not sure if they pertain to the PIC24FJ1024GB610-I/PT crystal input.?

The datasheet is no PIC datasheet, so the resistors are not related to PIC.
For sure, if the PIC already has built in circuitry to drive a resonator (similar to XTAL) then you need to adjust the external resistor values. In best case you may omit them.
To be sure you need to read the PIC datasheet.

Also , crystal outputs are weak, so i am surprised they have a series 330R with it.

The low ohmic resistor is at the inverter output (low impedance) and at the resonator input.
There is no crystal, and no crystal output either.

PIC datasheet says:

For additional information and design guidance on
oscillator circuits, please refer to these Microchip
Application Notes, available at the corporate website
(www.microchip.com):
• AN943, “Practical PICmicro® Oscillator Analysis
and Design”
• AN949, “Making Your Oscillator Work”
• AN1798, “Crystal Selection for Low-Power
Secondary Oscillator”

Klaus

 

[cupoftea]

Thanks Klaus,
Having looked at your kindly supplied AN949, I am convinced that using this crystal on its own across the micro XTAL pins is going to be a disaster. The crystal obviously needs capacitors to ground as shown in AN949, as well as the addition of two resistors, one of which needs to be tuned to be 3 x the crystal effective series resistance.

I believe that using this crystal on its own , connected to a microcontroller would be a disaster, would you agree.?

AN949

https://ww1.microchip.com/downloads/en/appnotes/00949a.pdf

 

[betwixt]

The capacitors are already inside the crystal, that's why it has a ground connection. The PIC oscillator is already internally biased for 'linear' operation and the feedback level is set by using the appropriate oscillator mode.

Brian.

 

[FvM]

Why do you name the ceramic resonator "crystal". That's where the confusion of this thread starts. The resonator is a three-terminal component, the crystal a two-terminal one.