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Clocks

Anonymous
Not applicable

 As the subject states, I am interested in changing the 24 MHz crystal on my PSoC5LP development board to and 18.5 MHz crystal.  Will this cause me any problems or can I just swap it and go?

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1 Solution
ETRO_SSN583
Esteemed Contributor

USB needs 48 Mhz on PSOC, why 24 Mhz is used X 2.

   

 

   

If you need another frequency consider PSOC 4 which has fractional

   

clock dividers, or using verilog to generate a fractional divider to gen

   

the 18.5 Mhz. Note the downside is clock jitter in these techniques.

   

As well as absolute accuracy due to finite resolution of the technique.

   

 

   

    

   

          

   

http://www.cypress.com/?id=2401     Discussion half way down the page

   

 

   

Google "verilog fractional clock dividers", you will get a lot of hits.

   

 

   

 

   

Regards, Dana.

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3 Replies
JoMe_264151
Expert II

Afaik the crystal is used to precisely generate the clock for the USB-component(s). When you do not need USB capabilities there's nothing against changing the quartz.

   

 

   

Bob

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ETRO_SSN583
Esteemed Contributor

USB needs 48 Mhz on PSOC, why 24 Mhz is used X 2.

   

 

   

If you need another frequency consider PSOC 4 which has fractional

   

clock dividers, or using verilog to generate a fractional divider to gen

   

the 18.5 Mhz. Note the downside is clock jitter in these techniques.

   

As well as absolute accuracy due to finite resolution of the technique.

   

 

   

    

   

          

   

http://www.cypress.com/?id=2401     Discussion half way down the page

   

 

   

Google "verilog fractional clock dividers", you will get a lot of hits.

   

 

   

 

   

Regards, Dana.

View solution in original post

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ETRO_SSN583
Esteemed Contributor

Another approach, use a PSOC implemted PLL multiplier,

   

attached some basic info.

   

 

   

Regards, Dana.

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