Texas Instruments MSP430x1xx - Manual (Page 113)

Digitally-Controlled Oscillator (DCO)
7-13
Basic Clock Module
The user should consider two factors when reviewing the timing accuracy gen-
erated from the DCOCLK signal:
- Short term accuracy: Each individual cycle is as inaccurate as the DCO
steps.
- Long term accuracy: The accumulated average of many individual
cycles reduces the relative error down to less
than 1/3 percent, assuming a step delta of 10% and
a modulation period of 32.
Proper use of the modulation feature on the DCOCLK period increases the
accuracy by averaging the periods. The selected frequency set using the
control bits in the DCO and the modulation fraction defined by the control bits
in MOD sets the DCOCLK periods.
Note: Control of DCOCLK Frequency
The frequency of the digitally-controlled oscillator varies with temperature
and voltage and is different for each individual sample. The frequency can
be controlled by software if an external reference (such as the ACLK signal)
is used to measure the difference and to readjust the DCO frequency.