[time-nuts] Why these Crystal Frequencies?

Peter Bell bell.peter at gmail.com
Wed Dec 14 23:17:03 EST 2011


11.0592MHz is another crystal used for accurate baud rates -
especially on MCUs that had a 12MHz maximum clock (like the Intel
8051)
So is 9.8304MHz - used on a number of Mototola (now Freescale) MCUs
17.734475 is 4 times the PAL color burst frequency of 4.433619MHz

I'll see if I can think of anything else.

Regards,

Pete



On Thu, Dec 15, 2011 at 11:54 AM, Brooke Clarke <brooke at pacific.net> wrote:
> Hi Rex:
>
> Thanks, I had 14.7456 mis listed (off one row) as the 4X CB freq.  I've
> updated the table.
>
>
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com
> http://www.end2partygovernment.com/Brooke4Congress.html
>
>
> Rex wrote:
>>
>> Brooke,
>>
>> 14.31818  is 4x the analog color burst (~3.58)
>>
>> 18.432   divides cleanly for baud rates. I've used it as a PIC clock for
>> that. I think some of the others may be too, but I didn't recognize or do
>> the math to see.
>>
>>
>> On 12/14/2011 7:13 PM, Brooke Clarke wrote:
>>>
>>> Hi Pete:
>>>
>>> Maybe you can shed some light on the common xtal frequencies table where
>>> there's no explanation given?
>>> http://www.prc68.com/I/pdf/Crystal_Freq.pdf
>>> An answer is not it's an "even" frequency or "it's an even binary
>>> frequency. That's true for most of these and the factors are part of the
>>> table above.
>>> The question is why do they exist?
>>> such as:
>>> 32.0 kHz
>>
>> ...
>>
>>
>>
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