MSP430F5529 - ADC read from multiple pins

The ADC12 can only sample one input channel at a time. However, it can work on a 'list' of input channels, one after another.

To do so, you program one ADC12MCTLx (x = 0..15) for each input channel. 'x' is just an index number and not related to the input pin, so you can start with ADC12MCTL0, even if the first channel to sample is A6. The number of this first ADC12MCTLx register for such a 'sequence' is the one to write at ADC12CTL1. The last ADC12MCTLx gets the EOS bit set to indicate the end of the sequence. You can configer the individual ADC12MCTLx register for any input channel.

Next is that you need to tell the ADC12 that it shall sample a sequence. THis is done by setting ADC12CONSEQ_1

You may also chose to either trigger each conversion of teh sequence individually, or do them all at once as fast as possible. In the latter (recommended) case, set ADC12MSC bit.

Now you start the ocnversion by setting the ADC12SC bit and when it clears again (or when the ADC12IFG.x bit of the last index of the sequence is set), you'll have the result for the channel configured in ADC12MCTLx in ADC12MEMx.

It is a bad choice that in your demo code, the ADC12MCTL7 register was used to sample A/ input, as this implies a connection between ADC12MCTLx and Ax that doesn't exist. Your sequence may as well be "A5,A3,A6,A3" (note the duplicate, so A3 is sample dtwice as often as the others) or anything else.

Jens-Michael Gross said:

It is a bad choice that in your demo code...

I often find that the example/demo code does not necessarily demonstrate the best way to accomplish a task, especially when thinking in terms of incorporating the functionality into a larger program.

Brian Boorman said:

I often find that the example/demo code does not necessarily demonstrate the best way to accomplish a task, especially when thinking in terms of incorporating the functionality into a larger program.

Hi Jens-Michael,

Thank you for your response.  I have not had the chance to try out your suggestion.  I would like to discuss what I have worked out for learning purposes and then try your suggestions.

I have implemented code similar to what i posted above (less the highlighted portions) as follows:

{1}    AcquireSignal()

    Reads 90 samples from P6.6, stores to signal_vector[ ]

{2}    AcquireSignal2()

    Reads 90 samples from P6.7, stores to signal_vector2[ ]

{3}   AcquireSignal3()

    Reads 90 samples from P7.0, stores to signal vector3[ ]

What my program currently doing is calling all three of these and then printing the results to the LCD.  However, different ordering of this process results in  unexpected/undesired behavior (ie {1} - {2} - {3} has unexpected results, {3} - {2} - {1} functions correctly).  Where in the code is the mux actually switching the input pin?  I understand my implementation is not the best way to approach this, but I suspect that the undesirable behavior is a result of improper mux switching.

Vincent Din said:

Where in the code is the mux actually switching the input pin?

You can imagine the ADC12MCTLx registers as lines of a script. Each ADC12MCTLx register defines several actions: Input pin to use, reference to use, and whether this is the last 'line' of the 'script'.

ADC12STARTADD_x in ADC12CTL1 defines, on which 'line' of the 'script' to start. Depending on the conversion mode, it staretrs with this ADC12MCTLx register and converts depending on the settings found there, then either stops (single conversion), repeats (repeated single conversion) or continues with the next ADC12MCTLx register, doing what is defined there (sequence) until it reaches oen with the EOS (end of sequence) bit set.

Thsi way, you can program sequence of up to 16 independent conversions, and for each one you can freely define which input puin to use, which reference (internal, external or VCC, but you cannot switch between internal 1.5 and 2.5V) to use and whether it is the last one of a sequence.

You can even pre-define multiple independent sequences and then start one or the other (with ADC12STARTADD_x) when you need them. Or you have a sequence but sometimes run the second half only and sometimes the complete number of conversions, depending on where you set ADC12STARTADD_x.

In your code, when you run one input n times, then the next one for n times, you can either change the input channel in the ADC12MCTLx register or program different ADC12MCTLx registers and change the ADC12STARTADD_x setting.

Note that before changing the ADC12STARTADD_x value, or any of the ADC12MCTLx registers, you need to clear the ADC12ENC bit first. All bits that are grey on the users guide register description can only be modified safely when a certain other bit is set or cleared (e.g. SWRST for the USCI). Else the outcome is undefined.