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MSP430 Ultra-Low Power 16-bit Microcontroller Forum
Ability to turn off internal clock sources for MSP430F643X family members
Hello, we are current MSP430F449 users and due to the sensitivity of the receiver that we are using it in have had to write our code in such a way that, while running the ADC peripheral using the low frequency 32768 watch crystal oscilllator, we had to use one of the low power modes and further turn off the DCO ring oscillator to get the ADC input to be quiet enough. We are considering a new product that is equally if not more sensitive, but requires the processor to be ran at speeds up to 20Mhz. That said, we are considering the MSP430F643X members as possible candidates. My question is this: Can we turn off all of the extra internal oscillators to reduce system noise (power isn't the issue in this case) and run exclusively from an externally supplied clock source perhaps after running some code to set the thing up correctly? Note that it is NOT good enough to have the processor running on a different clock source while letting the other sources idle, it turns out that the oscillations are still detectable unless we can actually shut them off when we are not using them.
The 5x/6x family MSPs have a vastly improved clock system.If not used by any hardware, you can switch off all internal clocks and oscillators except for the ~12kHz VLO.So if ACLK, SMCLK and MCLK are running from an externally supplied TTL-level clock, all other sources can be deactivated or will do so automatically. However, some will be automatically activated if considered 'required'. Such as MODOSC, if a flash write operation is started or the an A/D conversion is started with default clock source (MODOSC). Or the DCO, if a fault is detected on the external signal. Or LFXT1/REFO if the FLL is active.
But if you're careful, yes, you can have everything disabled while the CPU is running from an external clock signal.
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