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ealdaz

Are MSP430 wake up times clock source dependent?

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Right on the money Doc. In addition to those external influences, crystals can be made of different materials (typically quartz,) material itself can be cut different ways, and in case of 32kHz crystal, material is also cut in to a tuning fork shape. All of those can affect wake-up time. 32kHz crystals are the ones that take longest.

 

And here's a quote from the book mentioned earlier (pg 34):

Crystal: Accurate (the frequency is close to what it says on the can, typically within 1 part in 105) and stable (does not change greatly with time or temperature). Crystals for microcontrollers typically run at either a high frequency of a few MHz to drive the main bus or a low frequency of 32,768 Hz for a real-time clock. The disadvantages are that crystals are expensive and delicate, the oscillator draws a relatively large current, particularly at high frequency, and the crystal is an extra component and may need two capacitors as well. Crystal oscillators also take a long time to start up and stabilize, often around 105 cycles, which is an unavoidable side effect of their high stability.

 

Resistor and capacitor (RC): Cheap and quick to start but used to have poor accuracy and stability. The components can be external but are now more likely to be integrated within the MCU. The quality of integrated RC oscillators has improved dramatically in recent years and the F20xx provides four frequencies calibrated at the factory to

within

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Thank you all for your replies, this is very helpful information and exactly what i was after... I will digest it all carefully.

 

It does seem on first light that the conclusion is (as per GeekDoc and RobG) that the MSP430 will wake up very quickly when using the internal DCO, and that when using an external Xtal, it has to wait for it to stabilise (order of ms) as it doesn't have a special "magic mode" that accelerates the process.

 

Again thank you all!

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... when using an external Xtal, it has to wait for it to stabilise (order of ms) as it doesn't have a special "magic mode" that accelerates the process.

No magic, but some MSP430 members do have programmable oscillator power levels for external crystal XT2. You could use a higher power level to start it, and then switch to a lower power level to keep it going. I do not remember which device or which document.

 

32kHz crystal is beyond help in this respect. The "solution" is to lower the power consumption so that you can keep it on all the time. I think a coin cell can run it for a few years.

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If you do happen to use a 32kHz crystal, check out TI's App Note slaa322b.

 

It goes into detail about how a crystal works, what will make it fail and how to design your circuit for optimal operation.

 

It's a good one to bookmark.

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