[time-nuts] teensy as time capture device

cfo xnews5 at luna.dyndns.dk
Thu Sep 24 10:13:41 EDT 2015


On Thu, 24 Sep 2015 05:30:35 -0700, Jim Lux wrote:


> 
> What would be interesting is if there's a pin on the Arduino/Teensy that
> you could feed a high quality oscillator to, and then do counting with
> that.  The K20 microcontroller has a mindbendingly large number of
> features and alternate pin functions.

As i see it, from the DS. , it seems like there are 2 options.

External Oscillator (the system clock clock) , 
or External Timer clock (limited to system clock/4)

Electr. specs
https://www.pjrc.com/teensy/K20P64M72SF1.pdf

Family Ref
https://www.pjrc.com/teensy/K20P64M72SF1RM.pdf


Seems like the EXTAL pin (main oscillator) accepts an Oscillator signal 
(max VDD + 0.3v) (Electr specs pg.10)

Ext Osc Connection (Family ref. pg. 526)

Also see PLL jitter (Electr specs pg.27 table 14)


There is a possibility to clock the FlexTimerModule by an external clock  
(FTM_CLKIN/EXCLK - Max freq is Mainclock/4) , 
see (Family Ref. pg. 113, 214 & 774)


If using EXTAL and USB , you want to make sure that the USB part still 
gets it's 48Mhz (via the PLL mul/div).
Maybe divide 10Mhz (XTAL) by 2 , and mul by 48, in the PLL.


Rgds
CFO - Denmark




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