hello all;

now I am using MSP430F4270, and i'd like to measure the voltage of the battery, if the battery low the microcontroller will give warning.

so i just connect power supply with voltage divider resistor(1.5M and 100K) to A4+ channel analog, but when I debug my program with FET, whenever it takes the ADC result the SD16MEM0 values is always 0xFFFF

when i measure the A4+ pin is only 0.15V, can someone tell me why,

really appreciate for the help,

here is my code..

#include <stdio.h>
#include <math.h>
#include <msp430x42x0.h>
#include "in430.h"

#define LOW_BAT 0xAEEF

void main( void )
{
// Stop watchdog timer to prevent time out reset
WDTCTL = WDTPW + WDTHOLD;
Init_LCD(); // initialize LCD
Init_Port(); // initialize port
// FLL_CTL0 |= XCAP14PF;
// Delay(4);

Display_all(); // display all character in LCD
Init_ADC();
_EINT(); // enable interrupts

while(1)
{
Display_sign(M,On);
Measure_Bat(); //measure ADC value
}

}

void Init_ADC(void)
{
unsigned int i;
SD16AE |= SD16AE3; // SD16 External Input Enable 4 (A4+ and A4-)

SD16CCTL0 |= SD16SNGL ; // , single conversion mode
SD16INCTL0 |= SD16INCH_4; // SD16 Input Channel select A4
SD16CTL = SD16REFON + SD16SSEL_1; // SD16 Switch internal Reference(1.2V) on, clock source SMCLK
//Delay(6); //delay 5 ms for Vref start up
for (i = 0; i < 0x3600; i++);

unsigned int ADCresult;

void Measure_Bat(void)
{
SD16CCTL0 |= SD16SC; //start conversion

while ((SD16CCTL0 & SD16IFG)==0);
ADCresult = SD16MEM0;

if( ADCresult < LOW_BAT )
{
Display_sign(Bat,On);

}
else
{
Display_sign(Bat,Off);

}

 

If that is 5 volts, the most you can get out of the divider is 315 millivolts if the big resistor is on top. The input impedance of the A to D pin is probably small enough that it causes the other drop. Try 100K & 100K.

 

Please post your schematic.

Also have you tried looking at TI's appnote for using this adc?

Please use the CODE tags and post your complete code... what you have there is hard to read and looks like it is missing curly braces and such. If you have nicely formatted and commented code people are more likely to take time to help. Help us help you