INTOSC2 starts up in internal resistor mode. To enable the use of a precision
external resistor, use the following steps:
- Switch OSCCLKSRC source to
INTOSC1 by setting CLKSRCCTL1.OSCCLKSRCSEL, followed by necessary delay for
clock transition
- Use driverlib function
"ASysCtl_setExtRCounterDelay(ASYSCTL_EXTR_COUNTER_DELAY_2048);" to set required
clock transition time.
- Enable ExtR mode using driverlib
function "SysCtl_setIntOSC2_Mode(SYSCTL_INTOSC2_MODE_EXTR);", followed by a
delay of 10000 cycles (can use "SysCtl_delay(10000U);" function from driverlib
to achieve a total 50009 cycles and provide additional buffer time).
- Wait until "ASysCtl_getExtROscStatus()" equals
"ASYSCTL_EXTR_ENABLE_COMPLETE"
- Switch OSCCLKSRC source back to
INTOSC2 by setting CLKSRCCTL1.OSCCLKSRCSEL, followed by necessary delay for
clock transition
After the steps above are completed,
INTOSC2 uses the ExtR. Actions such as PLL locking must be initiated after all steps
and included settling delays are complete.