pic 18F4550: local variable problem, - c

Question

I'm using the pic18F4550 with microchip v8.63 and with the C 18 compiler. I'm using a LDR that retrieve the value of the led (not on my picdem board) (red, green and blue) these values are stored in a variable after each conversion. Afther that when I press the button S2, I come into the method ISR: this part works.
But now: I try to compare the variable red, green and blue in the if's: but I think that it not happen, he just go to my 'else' (led RB3 on my picdem board burns).
#include <p18f4550.h>
/** V E C T O R R E M A P P I N G *******************************************/
extern void _startup (void); // See c018i.c in your C18 compiler dir
#pragma code _RESET_INTERRUPT_VECTOR = 0x001000
void _reset (void)
{
_asm goto _startup _endasm
}
#pragma code
void ISR (void);
#pragma code _HIGH_INTERRUPT_VECTOR = 0x001008
void _high_ISR (void)
{
_asm goto ISR _endasm
}
#pragma code _LOW_INTERRUPT_VECTOR = 0x001018
void _low_ISR (void)
{
;
}
#pragma code
/******************************************************************************/
// global variable, value off LDR.
unsigned int var1ADRESH = 0x00;
unsigned int color_red = 0;
unsigned int color_green = 0;
unsigned int color_blue = 0;
void main (void)
{
TRISD = 0x00; // PORTD als uitgang
RCONbits.IPEN = 0; // prioriteit uit
INTCONbits.GIE = 1; // enable interrupt
INTCONbits.RBIE = 1; // interrupt portB aan
//= set up port =
TRISAbits.TRISA0 = 1; // Set RA0/AN0 to input
//leds
TRISAbits.TRISA3 = 0;
TRISAbits.TRISA4 = 0;
TRISAbits.TRISA5 = 0;
LATAbits.LATA3 = 1;
LATAbits.LATA4 = 1;
LATAbits.LATA5 = 1;
ADCON0 = 0b00000000; // Set channel select to AN0
ADCON1 = 0b00001110; // Configure RA0/AN0 as analogue
ADCON2 = 0b10101010; // Right justified result
// TAD 12 and FOSC 32 - may need to adjust this
// depending on your clock frequency (see datasheet)
while(1)
{
_asm sleep _endasm
}
}
#pragma interrupt ISR
void ISR (void)
{
if (INTCONbits.RBIF==1) {
//conversie blauw
LATAbits.LATA3 = 0;
ADCON0bits.ADON = 1; // Enable ADC
// read LDR value.
ADCON0bits.GO = 1; // Set the GO bit of the ADCON0 register to start the conversion.
while (ADCON0bits.GO); // Wait until the conversion is complete.
ADCON2bits.ADFM = 0; // read result as 8-bit. (dus data in ADRESH) !
//= read data in ADRESH =
var1ADRESH = ADRESH; // reading value from LDR
color_blue = ADRESH; //waarde in blauw
//conversie rood
LATAbits.LATA3 = 1;
LATAbits.LATA4 = 0;
ADCON0bits.ADON = 1; // Enable ADC
// read LDR value.
ADCON0bits.GO = 1; // Set the GO bit of the ADCON0 register to start the conversion.
while (ADCON0bits.GO); // Wait until the conversion is complete.
ADCON2bits.ADFM = 0; // read result as 8-bit. (dus data in ADRESH) !
//= read data in ADRESH =
var1ADRESH = ADRESH; // reading value from LDR
color_red = ADRESH; //waarde in blauwe steken
//conversie groen
LATAbits.LATA4 = 1;
LATAbits.LATA5 = 0;
ADCON0bits.ADON = 1; // Enable ADC
// read LDR value.
ADCON0bits.GO = 1; // Set the GO bit of the ADCON0 register to start the conversion.
while (ADCON0bits.GO); // Wait until the conversion is complete.
ADCON2bits.ADFM = 0; // read result as 8-bit. (dus data in ADRESH) !
//= read data in ADRESH =
var1ADRESH = ADRESH; // reading value from LDR
color_green = ADRESH; //waarde in blauwe steken
// alles uitzetten
//PORTB = 0b1111111;
LATAbits.LATA5 = 1;
if(color_blue > color_red && color_blue > color_green){
//blauw
LATDbits.LATD0 = 1;
}
if(color_red > color_blue && color_red > color_green){
//rood
LATDbits.LATD1 = 1;
}
if(color_green > color_red && color_green > color_blue){
//groen
LATDbits.LATD2 = 1;
}
else {
LATDbits.LATD3 = 1;
}
}
INTCONbits.RBIF = 0;
}

Answer 1

Try to set all three of LATA3,4,5 before every readout?
Set TRIS for D0..2

Answer 2

I detect a few weird things (but I confess none might be the source).
Once you set the LATA bits, does the LDR immediately changes val? Of course not, but is it a matter of ns, us or ms?... I don't see any delays for LDR settling times.
You are always sleeping so it's probably required to set the ADON=1 (check DS). However, check the device DS for how long does the AD needs to get it's internals up and ready after setting ADON=1. On that subject, once ADON=1 you shouldn't and don't need to set it over again the the next two acquisitions.
The same thing about the format of the result. Set it once, and do it before the GO=1. Don't re-set every conversion.
If you're using only 8bit results, why the unsigned int? (btw, int is pretty dangerous in microcontrollers. Use short and chars and always explicit signdness).
Why the var1ADRESH assignment then color_xxx? when do the LATD bits eventually get =0?
Your If else only works on the last branch. I believe you intended a if{} else if{} else if... structure.