MSP430F2274 DCO Start-up time

Hello,

in the family user guide it states something about code startup execution after power up clear ( PUC), in less than 2 µs therefore the DCO has to be way quicker i think.

It is in the FamilyUserGuideBasi Clock Module+ page 279.

I'd expect the DCO wakeup time to be the same for LPM and power-on. For the default frequency setting in the 1MHz range this would be 2µs.

However, the datasheet also lists the Td(BOR), the tiem between reaching the minimum voltage and releasing BOR condition, which can be as large as 2000(!)µs.

The 2µs in the datasheet are the time from PUC to code execution.
PUC means the moment where most hardware registers (but not all) are re-initialized and the reset vector is read. Assuming the default 1MHz DCO frequency of 1MHz (= 1µs clock cycle), this doesn't mean anything more than the time needed to read the reset vector and the first instruction of the startup code (in case of a C program, else the assembly program main)

It does not include the time for BOR and BOR delay (which also applied to a manual reset on RST pin), the CPU init code (that initializes some registers which aren't touched by PUC), checking the BSL entry.

So from power-on to first executed instruction, it takes much, much, much longer. And the DCO is there from the very beginning.

Also, DCO settlign is only required when changing the RSEL value. Switching between different DCO taps using DCOx and MODx bits does not require any settling time - the different taps are synchronized. If RSELx is changed, there might be one crippled DCO pulse, so it is advised to set an MCLK divider of at least /2 to avoid a CPU crash due to overfrequency.