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After having a sneak-a-peek of the MSP430’s clock system, we have to know some basic rules of using
the BCS+ module of MSP430G2xx devices:
• XT2CLK and LFXT1CLK high frequency mode are both unavailable. We can’t use them.
• DCOCLK is the most reliable clock source and should be used for both MCLK and SMCLK.
• DCOCLK is dependent on VDD and so set VDD in GRACE before trying to setup BCS+.
• Pre-calibrated DCOCLK values should be used as they offer good tolerance figures.
• It is not wise to use custom DCOCLK values as accuracy issues surface.
• If LFXT1CLK is used and needs precise timings, use a good clock crystal/TCXO/clock source.
• Use proper capacitance value for LFXT1CLK when an external crystal is used.
• Unused clock sources should be disabled to reduce power consumption.
• Pins that connect with external clock sources should be set as inputs if they are not used.
• Add a system start up delay of about 10 – 100ms to allow stabilization of clock sources.
• Clock outputs are available only in certain pins. If used, they are needed to be set accordingly.
• Use oscillator fault interrupt if needed. This becomes extremely necessary to ensure fail-safe
clock operation when external clock sources are used alongside internal clock sources.
• For time sensitive hardware like timers, try to use a reliable clock source.
• Check for warnings in GRACE.
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