MSP430FG6426: CTSD16: internal temp sensor not working?, voltage ranges

Hi Peter,

I looked further into this example code and it is incorrect. The TLV data (this is found in the datasheet) contains the calibration values for the CTSD16 and also with regards to the internal temperature sensor. 

Looking at the MSPFR413x_adc10 temperature example, we can use the same process with this device and the calibration data stored in the TLV data. Here are the steps I took to convert the MSPFG6426 example.

1. Find the memory location for the temperature calibration data found in the TLV table
   1. 
2. Create #define for the memory addresses for ease of reading
   1. #define CALADC_30C *((unsigned int *) 0x1A1E)
   2. #define CALADC_85C *((unsigned int*) 0x1A20)
3. Since we are using the calibration data we need to change our formulas, these calibration values are based on Celsius.
4. Here are the equations based on the FR413x example
5. results[1] = (results[0] -  CALADC_30C) * (85-30) / (CALADC_85C - CALADC_30C) + 30
   results[2] = results[4] * 9/5 + 32;

Below I'll post the whole code section so you can copy and paste to test yourself.

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//******************************************************************************
//  MSP430FG662x Demo - CTSD16, Using the Integrated Temperature Sensor, Ext. Res.
//
//  Description: This program uses the CTSD16 module to perform a single
//  conversion on a single channel which is internally connected to the CTSD16's
//  temperature sensor and an external resistor feeding the CTSD16 clock. Once
//  the conversion is completed, the result is stored in a variable then converted
//  into Celsius and Fahrenheit values.
//
//  Test by setting a breakpoint at the indicated line. Upon reaching the breakpoint
//  the conversion result will be stored in the results array. The result will
//  then be taken and converted into degrees K, C, and F and be saved in the same
//  array.
//
//  ACLK = 32kHz, MCLK = SMCLK = Calibrated DCO = 16.384MHz, SD_CLK = 1.024MHz
//  * Ensure low_level_init.c is included when building/running this example *
//
//  Notes: For minimum Vcc required for CTSD16 module - see datasheet
//         1nF cap btw Vref and AVss is recommended when using 1.2V ref
//
//  Sensor's temperature coefficient is 2.158mV/K (from datasheet)
//  Sensor's offset voltage ranges from -100mv to 100mV (assume 0)
//  Vsensor = 1.32mV * DegK + Vsensor_offset (assuming 0mv for offset)
//  Vsensor = (CTSD16MEM0)/32767 * Vref(mV)
//  DegK = (CTSD16MEM0 * 1200)/32767/2.158 = (CTSD16MEM0 * 1200)/70711
//  DegC =  DegK - 273
//  DegF = (DegC * 9/5) + 32
//
//
//               MSP430FG662x
//             -----------------
//         /|\|                |
//          | |                |
//          --|RST             |
//            |                |        (A0.6+/- connected internally)
//            |A0.6+      VREF |---+    (to CTSD16's temperature sensor)
//            |A0.6-           |   |
//            |                |  -+- 1nF
//            |                |  -+-
//            |                |   |
//            |           AVss |---+
//
//  M. Swanson
//  Texas Instruments, Inc
//  April 2014
//  Built with Code Composer Studio v5.5
//******************************************************************************
#include <msp430.h>
#define CALADC_30C *((unsigned int *) 0x1A1E)
#define CALADC_85C *((unsigned int*) 0x1A20)
unsigned int  results[3];                   // CTSD16 Conversion and Temp Results
                                            // results[0] = raw CTSD16 results
                                            // results[1] = temp in C
                                            // results[2] = temp in F

void main(void) {
    WDTCTL = WDTPW | WDTHOLD;               // Stop watchdog

    CTSD16CTL = CTSD16CLKR | CTSD16REFS;   // Use internal ref, external resistor
    CTSD16CCTL0  |= CTSD16SNGL; //| CTSD16DF; // Enable interrupt
    CTSD16INCTL0 |= CTSD16INCH_6;           // Internal temp sensor
    CTSD16IFG &= ~CTSD16IFG0;               // Clear CH0 result interrupt
    CTSD16IE |= CTSD16IE0;                  // Enable CH0 result interrupt

    __delay_cycles(2000);                   // Delay ~120us for 1.2V ref to settle

    while(1) {
        CTSD16CCTL0 |= CTSD16SC;            // Set bit to start conversion
        __bis_SR_register(LPM0_bits | GIE); // Enter LPM0 w/ interrupts
        __no_operation();                   // For debugger

        // Calculate Temperatures in different scales
        results[1] = (results[0] -  CALADC_30C) * (85-30) / (CALADC_85C - CALADC_30C) + 30;
        results[2] = results[4] * 9/5 + 32; 
        __no_operation();                   // SET BREAKPOINT HERE
    }
}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=CTSD16_VECTOR
__interrupt void CTSD16_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(CTSD16_VECTOR))) CTSD16_ISR (void)
#else
#error Compiler not supported!
#endif
{
    switch (__even_in_range(CTSD16IV,CTSD16IV_CTSD16MEM0)) {
        case CTSD16IV_NONE: break;
        case CTSD16IV_CTSD16OVIFG: break;
        case CTSD16IV_CTSD16MEM0:
                   results[0] = CTSD16MEM0; // Save CH0 results (clears IFG)
                   break;
        default: break;
    }
    __bic_SR_register_on_exit(LPM0_bits);   // Wake up from LPM0
}

I was incorrect about the data format, 2's complement would be needed because the calibration data is formed on based on 2's complement. There is also an offset, which is not calibrated. If you do your own calibration I do recommend the offset version instead of 2's complement.

Regards,

Luke Ledbetter

Hi Peter,

I recommend reading section 1.13 in the User's Guide for information on using the TLV data. Below is a snippet for the ADC and CTSD16 Offset and Gain calibration. Slightly below this is a similar setup for the Temperature sensor.

Regards,

Luke