HELP on 16f877 ADC, MSB not changing

[elijah]

Hello, I'm using the ADC of 16F877 and I set it to 10 bits.
I want to see what value pops out everytime I read the analog port, the problem is I cant somehow get the MPLAB ICD2 debugger to work on this chip so I decided to just convert the value into its binary equivalent and output it to another port..

The problem is the the MSB (the 10th bit) seems to be not changing whether the value is in the upper half of the analog input or the lower half of the analog input. For example: I'm inputting 0-5Volts in the analog pin.
so for ranges 5 to about 2.5 the MSB should be high, and for about 2.499 to 0 the MSB should be low..The problem is it isnt changing, its always high which means the value just repeats (5V = 2.4999V).

pls help me!!!!! THANKS

here is my code..sorry if it's too long


#include "D:\my files\shigoto\new upconverter\feedback test kiban\program\test.h"


void send(int16 index,unsigned int16 reg,unsigned int16 comp)
{
int counter,n;

output_low(PIN_D4); //CS low
delay_ms(1);
//output_low(PIN_A1); //FS low
//delay_ms(1);


for(n=0;n<index;n++)
{

output_high(PIN_D5); //clk high
delay_ms(2);

if((reg&comp)!=0) //bit 15
{
output_high(PIN_D7); //data high
}
else
{
output_low(PIN_D7); //data low
}

delay_ms(2);
output_low(PIN_D5); //clk low
delay_ms(4);
reg<<=1;
}

//output_high(PIN_A1); //FS high
delay_ms(1);
output_high(PIN_D4); //CS
output_low(PIN_D7); //data low


}



void main()
{
unsigned int16 value;


output_high(PIN_A1); //FS high
output_high(PIN_D4); //CS low
output_low(PIN_D5); //CLK low
output_low(PIN_D7); //data low

setup_adc_ports(A0);
setup_adc(ADC_CLOCK_DIV_8);
set_adc_channel(0);

value=0;
delay_ms(100);


while(1){


value = read_adc();
send(10,value,512); //10 bits
delay_ms(400);

}



}

[Ttelmah]

Couple of comments, without looking deeply:
1), what is 'A0' equal to. The value for 'setup_adc_ports' for AN0 as an input, is 'AN0' not 'A0' (or RA0, on a much older compiler version). If A0, does not equal the right value, the ADC, might be getting it's reference voltage from somewhere else, or be misconfigured in some other similar way.
2) What is the clock rate?. Using clock/8 to feed the ADC, implies your crystal should not be above 5Mhz.
3) What is the compiler version?. This is something that should always be included in this sort of question, because of known problems, and changes in the compiler.

Best Wishes

[JohnKennedy]

I'm sure you have to add this line in your beginning of your program as the A/D defaults to 8 bit mode Can't do any harm to try it