MSP430 ADC

Hello, I am workin with MSP430F5438A too. I hope my answer help you, if you watch something wrong, tell me please.

Can I used the ADC_10 to take multiple measurements of a circuit?

You also may consul the device datasheet (MSP430F5438) because the User's Guide corresponds to a device family, so there is some modules that appears in the guide, but they are not avaliable in your device. Reading the datasheet, ADC_10 is not avaliable in 5438A, only ADC_12. And yes, you can take multiple measurments of a circuit.

I need to measure the input voltage 28 (volts)

Page 62 of F5438A datasheet, "Analog input voltage range" between 0 and Vcc, Vcc is the powered voltage whose maximiun value is 3.6 V ( datasheet info again ). So, initially, you can not measure this input voltage value.

I know that the ADC_10 as multiple memory storage registers , but wouldn't that effect the ISR? I also was thinking about the analog input pins that I would used on the msp430F5438A.

Read carefully the ADC_12 section in Users' Guide. It is the better place where you find a clear explanation. If you come from other uC ( in my case 8051 ), it is some different the ADC functionality in this uC, but writing some testing code and debugging you will understand.

Good luck.

Travis Pace said:

Can I used the ADC_10 to take multiple measurements of a circuit?

Basically, the ADC (both, ADC10 and ADC12) converts voltages relative to GND. And of course the input voltage must not exceed VCC (or, if you use one of the internal references, the reference voltage). Exceeding the reference resulty ins 0x0fff readings, exceeding VCC results in possible destruction of the MSP.

Travis Pace said:

I know that the ADC_10 as multiple memory storage registers , but wouldn't that effect the ISR?

The ADC12 has 16 independent storage registers which can be used to sample any combination and sequence of one of its 16 analog inputs. Interrupt can be triggered on any register update There are 16 independent IFG and IE bits, so you can trigger an interrupt after first half of conversions (double-buffering algorithm) or after a sequence is through. Just as you like. Or you can use (general purpose) DMA to move the results.

On the 5438A, you can sample up to 12 external voltages (and 4 internal ones, including VCC and temperature), each by a different pin. However, sampling takes place one-after-another and not simultaneously.

For measuring  28V may be you can use voltage divider to bring it close to reference for ADC unit.

I did some more research on the ADC_12 in the user's guide. Since I will be measuring the 28 volts DC using a voltage divider, I assume that I need to select the appropriate  reference voltage.  Would 2.5 Volts be an appropriate reference voltage? I know if all elses fails I can just add a voltage from the AVcc pin.

Also, for the  ADC12CONSEQx, I was thinking of  just doing  a single channel single conversion for each of the three analog inputs by changing the channels after each conversion is stored in memory. All of the measurements should give me the same voltage measurement anyway. I guess my question would be about the sequence of channels. Does the sequence of channels allow me to do multiple ADC conversions at the same time? I figure this can make more efficient coding as well as save more time by just calling one interrupt.

Travis Pace said:

Also, for the  ADC12CONSEQx, I was thinking of  just doing  a single channel single conversion for each of the three analog inputs by changing the channels after each conversion is stored in memory. All of the measurements should give me the same voltage measurement anyway. I guess my question would be about the sequence of channels. Does the sequence of channels allow me to do multiple ADC conversions at the same time? I figure this can make more efficient coding as well as save more time by just calling one interrupt.

If you use a sequence of channel mode, in the ISR you obtain all data conversions (that you have enabled) in the ISR. I could give you a little explanation because this ADC module has some characteristics that are different compared to 8051 for example ( I do not know with what uC you have worked before), but I am sure that it is better explained in the Users' Guide than I can do it. After reading it and writing some code, if you have any doubt, post here again, and we will try to help you again.

Travis Pace said:

Would 2.5 Volts be an appropriate reference voltage?

Travis Pace said:

Does the sequence of channels allow me to do multiple ADC conversions at the same time?

You can wait for the sequence to be complete by watching the ADC12IFG register for the final IFG bit popping up, or configure the interrupt to be triggered at the last conversion (or even for each single one, if you like). The results of all conversions are then waiting in the proper ADCMEMx registers.

Please, next time you post, include the ADC configuration and ADCMEMX register at least, by this way is easier find a solution.

First, when you say "a code that sends 2 V into ...", I suppose you are meaning  connect  a 2 volts supply at a uC pin.

The value you obtain in the register depends on the voltage reference and and uC voltage supply, hence, if we do not know the ADC configuration and power supplied to uC, it is difficult to resolve your question. In users' guide, page 602, it appears the conversion formula : N = 4095 * ( ( Vinput - Vref- ) / ( Vref+ - Vref- ) ). Thereby, the importance of knowing reference voltage and ADC configuration. For example, without enter in details like internal references and similar:

With Vinput  = 3 and  Vref+ = 3 and Vref- = 0, ADCMEMXX = 4095. If we change the reference to 3.3 volts, ADCMEMXX = 3723. In this uC, if Vinput > Vref+ (between admisible values), the value showed in the register is 4096.

And finally, it happens sometimes, have you tried to modify the input voltage and check that the memory register changes its value? It is not the first time I mistake with the pins configuration.

I’m working with msp430F5438A experimenter board. I’m sending 2 volts DC through the analog pin (A7) P6.7 and trying to store that value in memory register 7. I’m not exactly sure on what the voltage is on Vcc sends I’m connected through USB. I’m assuming the reference voltages could be 1.5 or 2.5 volts depending on the one I enable. Is there a data sheet out there for the experimenter board so I can know the default values or is the default values the same has the msp430F5438A. Below is example code I got off the website. I'm just using one conversion though. P6.7 analog pin (A7) off of the msp430F5438A experimenter board. I'm just trying to find something that I can build off on.

//******************************************************************************

//  MSP430F543xA Demo - ADC12_A, Sequence of Conversions (non-repeated)

//

//  Description: This example shows how to perform A/D conversions on a sequence

//  of channels. A single sequence of conversions is performed - one conversion

//  each on channels A0, A1, A2, and A3. Each conversion uses AVcc and AVss for

//  the references. The conversion results are stored in ADC12MEM0, ADC12MEM1,

//  ADC12MEM2, and ADC12MEM3 respectively and are moved to 'results[]' upon

//  completion of the sequence. Test by applying voltages to pins A0, A1, A2,

//  and A3, then setting and running to a break point at the "_BIC..."

//  instruction in the ISR. To view the conversion results, open a watch window

//  in debugger and view 'results' or view ADC12MEM0, ADC12MEM1, ADC12MEM2, and

//  ADC12MEM3 in an ADC12 SFR window.

//  This can run even in LPM4 mode as ADC has its own clock

//  Note that a sequence has no restrictions on which channels are converted.

//  For example, a valid sequence could be A0, A3, A2, A4, A2, A1, A0, and A7.

//  See the 5xx User's Guide for instructions on using the ADC12.

//

//                MSP430F5438A

//             -----------------

//         /|\|                 |

//          | |                 |

//          --|RST              |

//            |                 |

//    Vin0 -->|P6.0/A0          |

//    Vin1 -->|P6.1/A1          |

//    Vin2 -->|P6.2/A2          |

//    Vin3 -->|P6.3/A3          |

//            |                 |

//

//   M Morales

//   Texas Instruments Inc.

//   June 2009

//   Built with CCE Version: 3.2.2 and IAR Embedded Workbench Version: 4.11B

//******************************************************************************

#include "msp430x54xA.h"

volatile unsigned int results;           // Needs to be global in this example

                                            // Otherwise, the compiler removes it

                                      // because it is not used for anything.

void main(void)

{

  WDTCTL = WDTPW+WDTHOLD;                   // Stop watchdog timer

  P6SEL = 0x80;                             // Enable A/D channel inputs P6.7

  /* Initialize ADC12_A */

  ADC12CTL0 = ADC12ON+ADC12MSC+ADC12SHT0_2; // Turn on ADC12, set sampling time

  ADC12CTL1 = ADC12SHP+ADC12CONSEQ_1;       // Use sampling timer, single sequence

  ADC12MCTL6 = ADC12INCH_7+ADC12EOS;                // ref+=AVcc, channel = A7, end of sequence

  ADC12IE = 0x80;                           // Enable ADC12IFG.7

  ADC12CTL0 |= ADC12ENC;                    // Enable conversions

  while(1)

  {

    ADC12CTL0 |= ADC12SC;                   // Start convn - software trigger

    __bis_SR_register(LPM4_bits + GIE);     // Enter LPM4, Enable interrupts

    __no_operation();                       // For debugger

  }

}

#pragma vector=ADC12_VECTOR

__interrupt void ADC12ISR (void)

{

  switch(__even_in_range(ADC12IV,34))

  {

  case  0: break;                           // Vector  0:  No interrupt

  case  2: break;                           // Vector  2:  ADC overflow

  case  4: break;                           // Vector  4:  ADC timing overflow

  case  6: break;                           // Vector  6:  ADC12IFG0

  case  8: break;                           // Vector  8:  ADC12IFG1

  case 10: break;                           // Vector 10:  ADC12IFG2

  case 12: break;                             // Vector 12:  ADC12IFG3

  case 14: break;                           // Vector 14:  ADC12IFG4

  case 16: break;                           // Vector 16:  ADC12IFG5

  case 18: break;                           // Vector 18:  ADC12IFG6

  case 20:                                      // Vector 20:  ADC12IFG7

                                                                               // Move results, IFG is cleared

     results = ADC12MEM7;                 // Move results, IFG is cleared

     __bic_SR_register_on_exit(LPM4_bits);

  case 22: break;                           // Vector 22:  ADC12IFG8

  case 24: break;                           // Vector 24:  ADC12IFG9

  case 26: break;                           // Vector 26:  ADC12IFG10

  case 28: break;                           // Vector 28:  ADC12IFG11

  case 30: break;                           // Vector 30:  ADC12IFG12

  case 32: break;                           // Vector 32:  ADC12IFG13

  case 34: break;                           // Vector 34:  ADC12IFG14

  default: break;

  }

}

I do not know how the uC works when you configure a sequence of channel, but you only read one of the ADC registers. So if you only want to read one value, I would recommend you to use single channel conversion, I suposse that the nmonic is "ADC12CONSEQ_0", check in the header file and you do not have to use the ADC12EOS bit.

Moreover, the ISR is related to the storage register ADCMEMXX, not to the pin you use as input. So, with this configuration, the ISR you have to use is :

" case 18: break;                           // Vector 18:  ADC12IFG6" .

Another example, related to the ISR, with :

ADC12MCTL0 = ADC12INCH_2;

you have to use   "case  6: break;                           // Vector  6:  ADC12IFG0", because the storage register is ADCMEM00 althought you are reading the pin 2.

I know its been a while but I finally got a single channel working. Now I'm trying to add a sequence of channels, I know that setting the  ADC12CONSEQx bit will allow for a sequence of channels but is it that simple? I'm starting the conversions at analog input 13 and i'm assumming that I will just add analog input 14 to the ISR as well as set the EOS (End of Sequence) to ADCMCTL14.

P.S

I appreciate all that gave feedback in this forum, my progression is just slower than others.

Travis Pace said:

is it that simple?

There is no fixed relation between teh ADC12MEMx register and the input channel. Your sequence can begin with ADC12MCTL0 in which you program the first input you want to convert, then continues with ADC12MCTL1 where tyou define the second input you want to read. Not necessarily the next one. YOu can make jumps and patterns or read the same channel twice if you want. The last ADC12MCTLx gets the EOS bit set and ends the sequence. The first ADC12MCTLx register where the sequence starts has to be programmed into the ADC12CTL registers. The interrupt bits are set according to the ADC12MCTLx register that was 'done', not the input channel that was coverted.

Travis Pace said:

Does the sampling period effect that ?

However, on a static input voltage, the same smapling time should result in the same reading (+- noise).

But there is another thing: the ground reference. When current flows through your PCB, this causes a voltage drop on the traces. This includes GND. If total board current consumption vaires, this measn that different parts of the GND trace have different currents at different times and therefore GND ins't the same everywhere and everytime. This can easily cause some 'noise' on the readings. For this reason, some MSPs have a separate analog GND input which only connects points where GND is required as reference and no current is routed through.

Another possible problem is the reference you use. If you use VCC as reference, voltage ripples on VCC will affect the reading as the voltage reading of the ADC is the relation between reference and signal. If the signal is static but the reference isn't, this is the same as if the reference is static and the signal isn't.
If you use the regulated references, ensure that you meet all requirements. Some MSPs require external buffering of the internal reference, on some MSPs, the internal reference requires the ADC clock being lower thabn a certain frequency. Check datasheet and errata sheet.