On 9/24/15 7:13 AM, cfo wrote:
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.
I would think that the FTM_CLKIN would be the way to go.. keep the core
running at 48 and run 10 MHz in as EXCLK (since it's less than Mainclock/4)
Not sure I'd want to fool with the PLL programming: that's something
where there might be other stuff that makes assumptions about how it's
configured.
Now I have to look if the right pins come out to something I can see.
This is the MK20DX256VLH7 configuration.
Only FTM1 (0,1) and FTM2 (0,1) are configured I think.
"There are two external FTM_CLKINx pins that can be selected by any FTM
module via the SOPT4 register in the SIM module."
Looks like pin 32 and 33 on the chip
Tnx
Jim
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