something wrong with DigPot AD8402

[jruibarroso]

I'm using the driver code (AD8400.c) that comes with CCS and using this main code to test the digital Pot :

#include <16f870.h>
#device adc=8

#fuses HS,NOWDT,NOPROTECT,NOBROWNOUT,NOLVP
#use delay(clock=8388608)

#include <AD8400.c>
#include <flex_lcd_4x20_3.c>

int8 PotA=125;

int8 PotV=125;

#define VoltsMenos PIN_C7 // key V-
#define VoltsMais PIN_C0 // key V+




void main()
{

setup_adc_ports(AN0_AN1_AN3);
setup_adc(ADC_CLOCK_INTERNAL);
//setup_psp(PSP_DISABLED);
//setup_spi(FALSE);
setup_adc(ADC_CLOCK_INTERNAL);
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_256);
setup_timer_1(T1_INTERNAL|T1_DIV_BY_1);
setup_timer_2(T2_DISABLED,0,1);
int_count=INTS_PER_SECOND;
enable_interrupts(INT_RTCC);
enable_interrupts(GLOBAL);
init_pots ();
delay_ms(500);
lcd_init();
delay_ms(500);



WHILE (TRUE) {


printf(lcd_putc,"\f Volts %LU\n Amps %U",PotV,PotA);

if (input(VoltsMenos)) {PotV=PotV-10;}
if ((PotV)<1) {PotV=1;}
if (input(VoltsMais)) {PotV=PotV+10;}
if ((PotV)>256) {PotV=256;}

set_pot (1, PotV);

delay_ms(250);

}


}


With all this , the digital Pot. simply don't change at all is OHM, it's stucked at middle scale (5k)

Can anybody help me ?

[PCM programmer]

Read the AD8400 data sheet:
http://www.analog.com/UploadedFiles/Data_Sheets/248207866AD8400_2_3_c.pdf
It has a table on the right side of page 13, that shows the input value
for the Pot, and the corresponding resistance. The table shows values
from 0 to 255.

Look at your code. What value are you using as the maximum value ?
Compare it to the permissable value in the table.


Also, you have declared your Pot voltage variables as 8-bit (unsigned)
variables. What is the range of values that such as variable can hold ?
Look at your code. You are trying to put a value of 256 in those
variables. What is the actual value that the variable will be set to,
if you try to do this ? Answer these questions and you will solve your
problem.