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ADC10 and DTC (MSP430F2xx)

Roman T.
Prodigy 150 points
Other Parts Discussed in Thread: MSP430F2132

Hi there

I'm a bit confused on how the ADC10 and DTC works. In my current project with an MSP430F2132, I have to measure the signals on A0, A1 and A3. Note that I'm not using channel A2, so there is a gap in the sequence of the channels. I want to trigger the conversions by software ony by one and use the DTC for transfering the three values to an array. Each time a block of three values is transfered, an interrupt shall be generated. For this task, I set up the ADC10 and DTC as following:

ADC10CTL0  = ADC10ON + ADC10IE;
ADC10CTL1  = INCH_3 + ADC10SSEL_3 + ADC10DIV_1     // Start with ch. A3, use SMCLK @ 8 MHz / 2
             + CONSEQ_3;                           // Repeat-Sequence-of-Channels
ADC10AE0   = 0x0B;                                 // Use channels A0, A1 and A3
ADC10DTC1  = 3;                                    // Three conversions per block
ADC10SA    = (unsigned int) ConversionsArray;      // Array containing the conversion values
ADC10CTL0 |= ENC;

Apparently, the ADC10 nevertheless samples channel A2, but the conversion value of that channel is always 1023. It seems the ADC10 doesn't care of what channels are enabled as analog inputs in ADC10AE0 and just samples every channel starting from INCHx down to A0. Is this correct? Hence, do I have to use Single-Channel Single-Conversion Mode if I have to sample a sequence of channels with a gap in it, forcing me to change INCHx before starting a new conversion?

Thanks in advance, Regards

Roman

  • 0
    Guru 227245 points

    Yes, teh ADC10AE0 just enables or disables the physical analog lines. It does not tell which ones to use in the conversion process. Note that ADC10AE0 has no bits for the internal channels such as temp or VCC measuring. So if this register would define what channel to convert and what not, you couldn't measure these at all.

    The ADC10 just samples down from channel x to 0. If you don't need one in the middle, well, you'll get a superfluous conversion. And if you don't set ADC10AE0 for a channel you want, well, you'll get a bogus conversion on this one, as there is no connection with the outside.

    if the extra time needed for this superfluous conversion is an issue, you should consider connecting the A3 lien to A2 instead on the hardware side. :)

    The ADC12 on other devices goes a different way. There you have separate registers where you can define which channel to sample in which order. You can build a chain of up to 16 conversions and freely defines which one when. Even the same several times intermixed with different others. But then, the results on ADC12 cannot be automatically stored as the ADC10 can. You'll have to read teh results and store them away amnually or by programming the DMA controller if the device has one.

  • 0
    TI__Expert 6280 points

    In ADC10 module, since there is only one register to hold the conversion result, the DTC module should be used to do sequence of conversions.

    In your case, since you need to measure A0, A1 and A3 (one-after-another), enabling sequence of conversions will measure the A2 channel as well. What is connected externally to the P2.2/A2 pin of the device? Is this pin used as an input or output pin? As long as the P2.2/A2 pin is not used at all or used as an output pin, we should be able to use sequence of conversions and sample channel A2 as well but then just discard the A2 conversion results.

    Configuration code:

            ADC10CTL1 = INCH_3+ CONSEQ_1;            // A3-A0, single sequence  
            ADC10DTC1 = 0x04;                         // 4 conversions
            ADC10AE0 = 0x0B;                          // ADC10 inputs A0,A1,A3 option select    

    Regards,

    Bhargavi

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