Hi Celso,
The highest frequency you can get using the internal resistors is about
4MHz. However, the devices are specified for operation up to 8MHz, and
you can achieve this by attaching an external resistor to P2.5. You need
to program this pin to be an oscillator control pin using the P2SEL
register. The documentation doesn't specify suitable resistor values
properly, so you need to experiment a little.
Regards,
Steve
Celso Providelo wrote:
Is possible obtain 8 MHz in SMCLK using an 32.768 KHz at X1 ?
I had success until 4,050 MHz, not more than this ...
I'm using the following rotine adapted from Scatterweb :
void dco_init(unsigned long int freq)
{
/*DCO initialisation
SMCLK = DCOCLK
MCLK = DCOCLK
ACLK = 32768 / 8
*/
unsigned int Compare, Oldcapture = 0;
int delta = freq / 4096;
/* ACLK is divided by 8, RSEL = 7, XT2 is off.*/
BCSCTL1 = XT2OFF | DIVA1 | DIVA0 | RSEL2 | RSEL1 | RSEL0;
/* Init FLL to desired frequency using the 32762Hz
crystal DCO frquenzy */
BCSCTL2 = 0x00;
/* Stop WDT */
WDTCTL = WDTPW + WDTHOLD;
/* Delay for XTAL to settle */
do
IFG1 &= ~OFIFG;
while (IFG1 & OFIFG);
/* clear osc. fault int. flag */
IFG1 &= ~OFIFG;
/*init TA for capture */
CCTL2 = CCIS0 + CM0 + CAP; // Define CCR2, CAP, ACLK
TACTL = TASSEL1 + TACLR + MC1; // SMCLK, continous mode
while (1)
{
while ((CCTL2 & CCIFG) != CCIFG); // Wait until capture occured!
CCTL2 &= ~CCIFG; // Capture occured, clear flag
Compare = CCR2; // Get current captured SMCLK
Compare = Compare - Oldcapture; // SMCLK difference
Oldcapture = CCR2; // Save current captured SMCLK
/* if equal, leave "while(1)" */
if (delta == Compare)
{
break;
}
/* DCO is too fast, slow it down */
else if (delta < Compare)
{
DCOCTL--;
/* Did DCO role under? */
if (DCOCTL == 0xFF)
{
/* Select next lower RSEL */
BCSCTL1--;
}
}
else
{
DCOCTL++;
/* Did DCO role over? */
if (DCOCTL == 0x00)
{
/* Select next higher RSEL*/
BCSCTL1++;
}
}
}
/* Stop CCR2 function */
CCTL2 = 0;
/* Stop Timer_A */
TACTL = 0;
}
Any help will be nice
best regards.
