- Ask a related questionWhat is a related question?A related question is a question created from another question. When the related question is created, it will be automatically linked to the original question.
I am using the MSP4305529's 12 bit ADC to acquire voltage readings. 8 samples are taken then averaged by a SCALE_FACTOR of 3. The result is then stored in sum_adc_data.
sum_adc_data >>= SCALE_FACTOR;
I wanted to output the value as a voltage, so we stored the value in vout. In order to get the correct voltage we multiplied by the appropriate ADC12_RATIO (2500/4095).
vout = sum_adc_data * ADC12_RATIO;
the problem is that when I check the registers in CCS vout does not give me the appropriate value. I decided to just copy the value from the sum_adc_data to vout.
vout = sum_adc_data ;
I still obtained the same result for vout. Below I have provided the code and a screenshot of the registers:
#include <msp430.h>
#include <stdint.h>
#include "TI_LMP91000.h"
#include "TI_LMP91000_register_settings.h"
#include "TI_MSP430.h"
#include "TI_MSP430_hardware_board.h"
#include "TI_MSP430_i2c.h"
/*----------------------------------------------------------------------------*/
void ADC12_Init(void); // To init MSP430F5528 ADC12 & Start Conversion
/*----------------------------------------------------------------------------*/
#define NUM_OF_RESULTS 8 // Number of temp sensor samples to take
#define SCALE_FACTOR 3 // For averaging converted samples
#define ADC12_RATIO 0.61035 // 2500/4096 (2.5V reference & 12bit converter)
//******************************************************************************
void main(void)
{
uint8_t status = TI_LMP91000_NOT_READY;
uint8_t read_val[2]; // buffer to store register values
WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer
TI_LMP91000_LED_PxOUT |= TI_LMP91000_LED_PIN; // Set LED ON
TI_LMP91000_LED_PxDIR |= TI_LMP91000_LED_PIN; // Set pin direction is output
I2CSetup(LMP91000_I2C_Address); // Initialize I2C module
TI_LMP91000_MENB_PxOUT &= ~TI_LMP91000_MENB_PIN; // Enable \MENB Pin
TI_LMP91000_MENB_PxDIR |= TI_LMP91000_MENB_PIN; // Set pin direction is output
while (status == TI_LMP91000_NOT_READY)
status = LMP91000_I2CReadReg(TI_LMP91000_STATUS_REG); // Read device ready status
LMP91000_I2CWriteReg(TI_LMP91000_LOCK_REG, TI_LMP91000_WRITE_UNLOCK); // unlock the registers for write
LMP91000_I2CWriteReg(TI_LMP91000_TIACN_REG, TI_LMP91000_TIACN_REG_VALUE); // Modify TIA control register
LMP91000_I2CWriteReg(TI_LMP91000_REFCN_REG, TI_LMP91000_REFCN_REG_VALUE); // Modify REF control register
read_val[0] = LMP91000_I2CReadReg(TI_LMP91000_TIACN_REG); // Read to confirm register is modified
read_val[1] = LMP91000_I2CReadReg(TI_LMP91000_REFCN_REG); // Read to confirm register is modified
if ((read_val[0] != TI_LMP91000_TIACN_REG_VALUE) ||
(read_val[1] != TI_LMP91000_REFCN_REG_VALUE)) // test values took effect
while (1); // otherwise error
LMP91000_I2CWriteReg(TI_LMP91000_LOCK_REG, TI_LMP91000_WRITE_LOCK); // lock the registers
LMP91000_I2CWriteReg(TI_LMP91000_MODECN_REG, TI_LMP91000_MODECN_REG_VALUE); // 3-lead amperometric cell
ADC12_Init(); // Initialize MSP430F5528 ADC12 & Start Conversion
__bis_SR_register(LPM0_bits + GIE); // Enter LPM0, Enable interrupts
__no_operation(); // For debugger
}
// Description: Initialization of the ADC12 Module & Start Conversion
/*----------------------------------------------------------------------------*/
void ADC12_Init(void)
{
TI_LMP91000_VOUT_ADC12_PxSEL |= TI_LMP91000_VOUT_ADC12_PIN; // Enable A/D channel A0
REFCTL0 &= ~REFMSTR; // Reset REFMSTR to hand over control to
// ADC12_A ref control registers
ADC12CTL0 = ADC12ON+ADC12SHT0_8+ADC12MSC; // Turn on ADC12, set sampling time
// set multiple sample conversion
ADC12CTL0 |= ADC12REFON+ADC12REF2_5V; // Turn on Ref Gen & set to 2.5V
ADC12MCTL0 = ADC12SREF_1; // Vr+ = Vref+ and Vr- = AVSS
ADC12CTL1 = ADC12SHP+ADC12CONSEQ_2; // Use sampling timer, set mode
ADC12IE = ADC12IE0; // Enable ADC12IFG.0
__delay_cycles(500); // delay to allow Ref to settle
ADC12CTL0 |= ADC12ENC; // Enable conversions
ADC12CTL0 |= ADC12SC; // Start conversion
}
/*----------------------------------------------------------------------------*/
// Description:
// ADC12 Interrupt Service Routine
/*----------------------------------------------------------------------------*/
#pragma vector=ADC12_VECTOR
__interrupt void ADC12ISR (void)
{
static uint8_t index = 0;
static volatile uint16_t results[NUM_OF_RESULTS]; // To store ADC output
static uint32_t sum_adc_data = 0; // accumulate and avg adc results
static volatile float vout; // lmp91000 vout
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: // Vector 6: ADC12IFG0
results[index] = ADC12MEM0; // Move results
sum_adc_data += ADC12MEM0;
index++; // Increment results index, modulo;
if (index == NUM_OF_RESULTS)
{
sum_adc_data >>= SCALE_FACTOR; // Divide by NUM_OF_RESULTS
vout = sum_adc_data * ADC12_RATIO; // LMP91000 vout
sum_adc_data = 0; // Set Breakpoint here & see measured vout
index = 0;
}
break;
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: break; // Vector 20: ADC12IFG7
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;
}
}
here are the results when we multiply with the ADC12_RATIO:
here are the results when the ratio is removed
shouldn't my vout have the same value as sum_adc_data since all i did was assign the value to vout? Is there a problem with float types in the msp430? How can I fix this issue?
Greetings Matt,
First of all thank you for the quick response! The data sheet reads:
vout = sum_adc_data * ADC12_RATIO // ADC12_RATIO is 0.6103
However, I still attempted the method you advised and I obtained the following results
this is still not accurate..I should obtain 1.67 Volts or 1670 mV in the vout register.
If you could assist me with the troubleshooting I would greatly appreciate it; thank you for the help!
Regards,
Jonathan
The attached project also shows the problem, with the static variables from the ISR function placed in main. 7635.msp430_statics_in_main.zip. It was generated in CCS 5.5 with MSP430 compiler v4.2.3 set to an output format of "eabi(ALF).
In the debugger the following screen shot shows the index and sum_adc_data variables have been correctly resolved to their address in RAM, but the results and vout variables have both been resolved to the incorrect address of 0x004604 in flash (which is the address in flash of main):
When the expression view was used to cast the RAM address where the vout variable really is (from the linker map file) the correct value was displayed. i.e. the floating point calculation has been performed correctly on the target and the problem is that the CCS debugger is not displayed the correct value of the vout (and results) variables.
First of all, thank you all for the time and help; I greatly appreciate it! Chester I referenced your post regarding the compiler error and by changing the compiler to V 4.2.1 and the output file to legacy COFF I was able to get the correct output value for vout.
Thanks!
Best regards,
Jonathan
**Attention** This is a public forum
