How to enable the external crystal oscillator in PSOC5.

[Anonymous]

Hello, All! I am new in PSoC world. Currently I am working on a project that require accurate frequency measurement. Since PSOC5 internal clock doesn’t accurate, using external crystal oscillator will provide  more accurate measurement.

   

I have an external crystal with part number ECS-240-20-33-CKM-TR, which is 24 Mhz crystal and 20 pF load capacitance. I already soldered this crystal on the PCB board next to PSOC chip at Pin 15[0] and Pin 15[1](I have attached schematic). I choose two 22 pF capacitors as load.

   

I followed procedure (AN54439_External crystal oscillators) and tried to enable this external crystal oscillator in PSOC creator, but it never work.  (See attached setup).

   

I don’t know why that it doesn’t work. Thank you for any help, I will really appreciate.  

[odissey1]

        jacob,, Please take a look on XTAL settings here http://www.cypress.com/comment/406171#comment-406171 Note that IMO is hoocked to XTAL and XTAL setting are different. The 22pf caps might be an issue, notice 12pf value on the picture. I used 14pf caps (20pf didn't work). Lastly, all XTAL wiring must be as short as possible.   

[Anonymous]

Thanks for the reply!
I know what you mean about using the lower caps. However, since my crystal has load caps spec as 20 pf, that's why I used 22 pf as load caps. (It is based on cypress website 
http://www.cypress.com/knowledge-base-article/mhz-external-crystal-oscillator-eco-cy8ckit-050-and-cy...) 
I will try it by using lower caps to see if is work. 

Thanks again.

[HeLi_263931]

When selecting the capacitors, you need to take into account the capacitance on the PCB and the MCU inputs. 12pF sound about right.

[Anonymous]

Thank you for the reply!

   

There is a formula for calculating the load capacitance. I assume Cstray is around= 7pF, if I pick up 12pF, 7+((12*12)/(12+12))= 13pF, which is lower than my crystal load capacitance. I used 22 as my C load, based of this formula. But it's not work....

   

update: I changed cap to 15pF, and it is still not work. I am considering does my layout did wrong? The distance between crystal to chip is around 0.14inch. 

I have attached layout pictures.

[rola_264706]

Have you scoped the Crystal and what kind of signal do you have on P15(0) and P15(1)?  Also did you mount the crystal correctly?

[rola_264706]

Also did you check halt on error in the Crystal setup screen.

[Anonymous]

Thanks for the reply!
I did check halt on error in the clock setup, but I didn't check the pin since I have to consider the capacitance in the probe, and it will load the crystal.

[HeLi_263931]

Look at the data sheet - the pin-out is shown from the bottom. Taking this into consideration your PCB looks wrong.

[Anonymous]

Thanks for the reply. You are right, we missed up top view /bottom view of crystal. Thank you! 

[odissey1]

hli is right, the PCB is no good. Only way to salvage the board is to glue XTAL upside down and hard-wire with 30AWG 😞

   

       

[Anonymous]

Thanks for the reply. Yes, you are right, the PCB is no good, it is upside down.  Thank you again.:)