Fixed Frequency Clock for FTM S08PA60

[corso66]

Hi,

I have a big lost time during many days to understand how Fixed Frequency Clock is generated, because i need a lower frequency for my PWM application.

It's impossible to know what is exactly the frenquency clock in my FTM1 module.

Idealy, i need a FTM clock at 12.8µs.

My PA60 running fully with an external cristal oscillator at 20Mhz, so 0,05µs of period busclock (BDIV0).

If i take datasheet, i set RDIV to 128, so 0.05 * 128 = 6.4µs :

ICS_C1 = 0x90;        //div128
ICS_OSCSC_RANGE = 1;

Then, datasheet explains ICSFFCLK is divided by 2, so  6.4 * 2 = 12.8µs:

And i use a div1 in my FTM1 module with external clock selected.

If i generate a minimal PWM signal at 50% of duty, oscilloscope give me a signal arround 20µs. And it's not a multiple of busclock divided... i don't understand. !!

Anyone can explain me how can i determinate the FFCLK exactly please ?

Thank you,

Sylvain

[corso66]

Hi @Julián_AragónM , thank you repli me.

It's true, i never check ICSOUT really as output pin. I will do it. However, I'm using also RTC for real Clock system, MTIM, I2C, SPI FTM and One-wire bus, based on Fbus at 20MHz, so i can confirm there is no problem. But i will check.

Here is my ICS and FTM modules settings (sorry i write too quick, i selected "Fixed Frequency Clock in FTM, not "External Clock)

	/* Set the ICS Internal Clock System */
	/* Enable 20MHz crystal to find 20MHz bus clock */
	ICS_OSCSC = 0x96; 							/* high-range, high-gain, oscillator required */
	while (ICS_OSCSC_OSCINIT == 0); 			/* waiting until oscillator is ready */
	ICS_C1 = 0x80; 								/* external clock reference (20MHZ) to FLL output */
	ICS_C2 = 0x00; 								/* BDIV = 0, prescalar = 1 */
	
	/* Set the ICS Internal Clock System */
	/* Enable Fixed Frequency Clock for FTM module ICSFFCK */
	ICS_C1 = 0x90;								/* RDIV = 128 with RANGE = 1 */
	ICS_OSCSC_RANGE = 1;						/* Give 20MHz / 128 = 156.250KHz so FFCK period = 6.4µS*/

	FTM1_SC = 0x11;		// No IT, up counting mode, div2, div2 => div4, Fixed frequency clock => FTM ON (6.4µs * 2 * 2 = 25.6µs)
	FTM1_C0SC = 0xA8;	// No IT, Edge-Aligned PWM

Thank you

[Julián_AragónM]

Hi @corso66,

From your code snippet, the configuration seems to be correct. Just help me checking if the FTMx_MODE is configured as Write Protected Disabled, since both CLKS and PS from FTMx_SC are write protected, and these bits can be written only if MODE[WPDIS] = 1.

Best regards,
Julián.

[Julián_AragónM]

Hi @corso66,

Could you firstly confirm if your external oscillator is running at the desired frequency? Measuring it directly and the enabling bus clock output pin.

Also, please share the configuration of the FTMx_SC register, as on the Clock Source Selection field, selecting "External Clock" may select TCLK1 as the clock source for FTM1.

Best regards,
Julián.