Can the PWM signals be run from the external crystal instead of the internal?
Your part should have FTM_CLKINx sources available onto a couple different pin options.
As you know that the MK22FN512VLL12 has EXTAL0/XTAL0 pins, of course, it can connect with external crystal. In default, the K22 use FEI mode, in other words, it use internal 32KHz IRC, but you can change the mode to FEE or PEE mode, which will use external crystal and use FLL or PLL to multiply the clock to 120mHz. The FTM module can use system clock or the clock source from FTM_CLKINx pins as EARL pointed out, the CLKs bits in FTMx_SC register specifies the clock source.
If you need accurate PWM cycle time, I suggest you use external crystal(connected to EXTAL0/XTAL0 pins), use PEE mode to multiply the clock to 120MHz, the FTM can use the 120mhz clock source as it's driving clock.
If you use KDS tools, you can create a project and select FRDM-K22 as project template, the FRDM-K22 use 8MHz external crystal, you can add the line #define CLOCK_SETUP 1 in system_MK22xx.h, the code will use PEE mode and set the system clock as 120MHz, the FTM can use the clock as driving clock.
Hope it can help you.
The FTM clock in said 120MHz examples being 60MHz of course == bus_clock.
Retrieving data ...