PSOC4200L: External Crystal for USB Application required?

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Anonymous
Not applicable

Hi everyone,

   

I've been scanning through the Cypress PSOC4200L Datasheet and USBFS Documents,

   

but I am not sure if an external cyrstal is required for USB Full Speed Application with the PSOC4200L?

   

Does anybody know?

   

Regards

   

Julian

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3 Replies
Bob_Marlowe
Level 10
Level 10
First like given 50 questions asked 10 questions asked

Welcome in the forum, Julian.

   

To maintain 0.25% accuracy required for USBFS you will need to trim the IMO using the optoin "to USB"

   

or

   

use an external crystal, either a 24MHz or a 32kHz watch crystal.

   

 

   

Bob

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i try trim usb get clock stop for period of max divisor, 64k, into 48000000.

so how does trim work?

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NoriTan
Employee
Employee
25 sign-ins 5 questions asked 10 sign-ins

Just select "USB" for the "Trim with:"  list box of the "IMO" in the "Configure System Clocks" dialogue.

GS004125.png

Please don't forget to enable the ILO too.

GS004126.png

The PSoC 4L periodically compares the IMO period difference and the SOF packet timing and trims IMO.  The ILO makes the timing to compare and trim.

Regards,

Noriaki

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