The MSP430x3xx devices are designed specifically to use a 32kHz
watch crystal, and then generate an internal high speed master clock
(MCLK) sourced from an independent, internal digitally controlled
oscillator (DCO). The MCLK is automatically stabilized in MSP430x3xx
devices to a user programmable value using internal frequency locked
loop (FLL) circuitry.
The MSP430x1xx and MSP430x4xx devices have one crystal oscillator that
accepts either a 32kHz or a high speed crystal. Some MSP430x1xx and
MSP430x4xx have a second crystal oscillator that accepts a high speed
crystal only. This allows one or two crystals to be connectedat the
same time and each one only used as necessary.
The MSP430x1xx and MSP430x4xx devices also have programmable internal
DCO which can enerate high speed clocks independent of any crystal.
In MSP430x4xx devices the FLL is also availble to stabilize the DCO to
a multiple of an external 32kHz crystal similar to MSP430x3xx devices.
Please refer to the datasheets and User`s Guides for the specific features
and capabilities of the different clock circuits and devices.