Hi,

I'm relatively new to the world of embedded programming but have been
making progress lately up until I tried to read 2 different A/D
channels.  My circuit is going to be a temperature control set to
display on a Hitachi 44780 LCD along with a 10k pot for reading the
temperature set-point.  I'm using a pic16f684 configured to use the
internal oscillator running at 8Mhz.  I have the LCD connected to
portc using a 4-bit operation for display.  A 10K thermistor is
connected to RA0 (pin 13) and a 10K pot connected to RA2 (pin 11).

I've taken the approach of getting the individual pieces to work by
themselves and am now trying to get them to work together.  The LCD
works fine, reading a temperature works as well as reading the pot
(using the 8 most significant bits).  My problem comes when I try to
read both the thermistor and the pot in subsequent loops.  If I turn
off the switch (sw) and only read either the pot or the thermistor, it
works.  If I oscillate between the two, neither reads an analog value
properly.

I tried to add a delay after I set the ADCON0 bits for each read but
that doesn't seem to have helped.  At this point I am at a bit of a
loss as to what needs to be done.  I'm hoping its something simple
that I have overlooked.  I have attached the code below, any insight
you can provide as to what I am doing wrong would be very much
appreciated.

Thanks,
Jason

/**
Thermo2.c
Jason Wambach

PICC program for the pic16f684 to read temperature and display on an LCD.

**/
#include <pic.h>
#include <math.h>
__CONFIG(FCMDIS & IESODIS & BORDIS & UNPROTECT & MCLRDIS & PWRTEN &
WDTDIS & INTIO);


int i,j,k,n,Count,b,sw;
unsigned int a;
double Temp;
//                          1234567890123456
const char TopMessage[]  = "Curr Temp: ";
const char BotMessage[]  = "Set  Temp: ";

#define E RC4
#define RS RC5

const int Twentyms = 1250;

const int Fivems = 300;
const int TwoHundredus = 10;

//4bit LCD Write Operation
LCDWrite(int LCDData, int RSValue)
{
	PORTC = (LCDData >> 4) & 0x0F;
	RS = RSValue;
	E = 1; E = 0;

	PORTC = LCDData & 0x0F;

	RS = RSValue;
	E = 1;
	E = 0;

	if ((0 == (LCDData & 0xFC)) && (0 == RSValue))
	{
		n =  Fivems;
	}
	else
	{
		n = TwoHundredus;
	}
	for (k = 0; k < n; k++);
	
}

//Write formatted decimal to LCD
TempDec(int i)
{
	int t;
	
	if (i >= 100)
	{
		t = i / 100;
		LCDWrite('0' + t, 1);
		i = i % 100;	
	}
	else
	{
		LCDWrite(' ', 1);
	}
	if (i >= 10)
	{
		t = i / 10;
		LCDWrite('0' + t, 1);
		i = i % 10;
	}
	else
	{
		LCDWrite('0', 1);
	}
	LCDWrite('0' + i, 1);
}

main()
{
	PORTC = 0;
	CMCON0 = 7;
	TRISC = 0;
	TRISA0 = 1;
	TRISA2 = 1;

	ANSEL  = 0b00000101;	
	ADCON1 = 0b00010000; //Clock Fosc/8 or 2uS

	//LCD Initialization
	j = Twentyms;
	for (i = 0; i < j; i++);
	PORTC = 3;
	E = 1; E = 0;  //Reset
	j = Fivems;
	for (i = 0; i < j; i++);

	E = 1; E = 0;  //Reset 2
	j = TwoHundredus;
	for (i = 0; i < j; i++);
	
	E = 1; E = 0;  //Reset 3
	j = TwoHundredus;
	for (i = 0; i < j; i++);

	PORTC = 2;
	E = 1; E = 0;
	j = TwoHundredus;
	for (i = 0; i < j; i++);
	
	LCDWrite(0b00101000,0);
	LCDWrite(0b00000001,0);  //clear lcd
	LCDWrite(0b00000110,0);
	LCDWrite(0b00001110,0);
	
	a = 0;
	Count = 0;
	sw = 0;
	while (1 == 1)
	{
		if (sw)
		{
			ADCON0 = 0b10000001; //Selected RA0, Right justified
			j = Twentyms;  //Delay for setup of A/D converter
			for (i = 0; i < j; i++);
			GODONE = 1;
			while (!GODONE);
			a = (ADRESH << 8) + ADRESL;
			//Temperature Calculation
			Temp = (1023.0 / (double)a) - 1.0;
			Temp = log(Temp);
	                Temp = 32.5 - (Temp / 0.019129);
			Temp = (9f/5f)*Temp+32;
			a = (int)Temp;
		}
		else
		{
			ADCON0 = 0b00001001;  //select RA2, Left justified result
			j = Twentyms;   //Delay for setup of A/D converter
			for (i = 0; i < j; i++);
			GODONE = 1;
			while (!GODONE);
			b = ADRESH;  //only care about 8 most significant bits
		}
		sw = sw ^ 1;  //switch between channels every loop
		
		//Only update the LCD every 10 iterations
		if (Count == 0)
		{
			LCDWrite(0b00000001,0);  //clear lcd
			for (i = 0; i< TopMessage[i] != 0; i++)
			{
				LCDWrite(TopMessage[i],1);
				//LCDWrite('0' + i, 1);
			}
			
			TempDec(a);  //Format and display
			LCDWrite(0xDF, 1);  //Degree symbol
			LCDWrite('F', 1);
	
			LCDWrite(0b11000000,0); //Move to 2nd line
			//2nd Line
			for (i = 0; BotMessage[i] != 0; i++)
			{
				LCDWrite(BotMessage[i],1);
			}
			
			TempDec(b);
			LCDWrite(0xDF, 1);
			LCDWrite('F', 1);
			Count++;
		}
		else
		{
			Count++;
			if (Count == 10)
			{
				Count = 0;
			}
		}	
		//delay
		for (i = 0; i < 255; i++)
		{
			for (j = 0; j < 129; j++);
		}
	}
	
}

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