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Setting up the DCO properly


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Thanks everyone for all the great information. I now know much more about the MSP430 DCO clock that I ever would have otherwise!

 

I solved my problem today. It turns out that my Tektronix TDS 224 scope has a problem. I took the Launchpad to work and used a high end 500MHz Tektronix scope and the clock was very stable. Except, if I used HF REJECT trigger coupling. This makes sense because with this coupling the scope has a low-pass filter that would prevent it from properly seeing the fast edges on my 10MHz clock and would cause the trigger point to vary. This gave me a clue concerning the TDS 224 which is only a 100MHz scope. My theory was that the low bandwidth of the TDS 224 scope was preventing me from properly triggering on the fast clock edges. But now I don't believe this is true because the TDS 224 has the exact same problem triggering on the clock when I set it to 1MHz. I now believe that something in the trigger function of the scope is bad.

 

Anyway, my clock problem is solved and I've successfully generated a PWM using the timer. Now I can move on the the next part of the project. Figuring out how to setup the ADC to continuously measure and generate an interrupt everytime it completes a measurement.

 

Thanks everyone.

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  • 2 weeks later...

I thought posting my numbers might be interesting for comparison. I'm off a little bit from

the results you obtained. I'm using an msp430g2553.

 

    DCOCTL = 0;
   BCSCTL1 &= ~(RSEL3 + RSEL2 + RSEL1 + RSEL0);
   BCSCTL1 |= (RSEL3 | RSEL2 | RSEL0);
   //DCOCTL  = 0;                     // 6.086MHz
   //DCOCTL  |= (DCO0);               // 6.415MHz
   //DCOCTL  |= (DCO1);               // 6.765MHz
   //DCOCTL  |= (DCO1 | DCO0);        // 7.17MHz
   //DCOCTL  |= (DCO2);               // 7.67MHz
   //DCOCTL  |= (DCO2 | DCO0);        // 8.31MHz
   //DCOCTL  |= (DCO2 | DCO1);        // 9.145MHz
   DCOCTL  |= (DCO2 | DCO1 | DCO0); // 10.125MHz

 

You ranged from 6.28MHz - 10.52MHz for the same settings.

 

-rick

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