ADC *** Locked. 2004 thread.

[Guest]

Hi,
the follow code doesn't work with emulator ice 2000 (MPLAB 6.40 & CCS 3.177) that isn't return the correct value. Why?

Thanks.


#include <18F452.h>
#DEVICE *=16 // Use 16 bit pointers to RAM
#DEVICE ADC=10
#include <STDLIBM.H>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=8000000)


void main()
{

int16 value;

setup_adc(ADC_CLOCK_DIV_8);
setup_port_a(RA0_ANALOG);
set_adc_channel( 0 );
while (TRUE)
{
delay_us(25);
value = read_adc();
}
}

[Ttelmah]

[Guest]

OK, but with setup_adc(ADC_CLOCK_DIV_16) or setup_adc(ADC_CLOCK_DIV_32) or setup_adc(ADC_CLOCK_DIV_64) doesn't work.

Thanks

[PCM programmer]

[xinyh]

read_adc() only return 8bits of the 10bits, so a new function is needed, anyone can help?

[Ttelmah]

[xinyh]

Hi Ttelmah,

Thanks for your reply!

My condition is like that, the analog voltage is 2.987V, for 10 bits, the hex value should be 2.987*(1024/5) = 263, but the value returned is 0063. The code is as below.

Best Regards!

#include <16f877.h>
#include <stdio.h>

#device ADC=10
#fuses HS,NOLVP,NOWDT,PUT, NOPROTECT
#use delay (clock=20000000)
#bit ADFM_BIT = 0x9F.7
#use rs232 (baud=9600, xmit=PIN_C6, rcv=PIN_C7)

void main() {
int value;
setup_adc_ports(RA0_ANALOG);
setup_adc(ADC_CLOCK_DIV_8);
ADFM_BIT = 1; // Right justify the A/D result

setup_spi(FALSE); //This function will initialize the SPI
setup_psp(PSP_DISABLED);
setup_counters(RTCC_INTERNAL,RTCC_DIV_2);//This function sets up the RTCC or WDT.
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_ccp1(CCP_OFF);
setup_ccp2(CCP_OFF);

SET_TRIS_A(0b0000001); //Set A0 as input
SET_TRIS_C(0b10000000); //Set C7 as input & C6 as output

// Read analog input voltages
set_adc_channel(0);
delay_ms(5);

do {
delay_ms(250);
value = Read_ADC();
printf("\n\r ADC-value: %4X \r\n", value);
} while (TRUE);
}

[Haplo]

I went through your code quickly and found two mistakes:

1. For a 20MHz crystal you need to set the ADC clock to 32TOSC, so you have to change that line in your code to:

setup_adc(ADC_CLOCK_DIV_32);


2. You've defined #device ADC=10, but you are using an 'int' variable to read the ADC (Mr.Hamlett had suspected right). Remember in CCS, 'int' is the same as 'int8' which is 8-bit variable. So change your code to:
int16 value;

And you'll also need to change your 'printf' statement as well to print out an int16 variable.

[xinyh]

Hi Ali,

You are right! In my CCS Vision, there are not int8 and int16, so I use long int, but the problem is same, maybe I will change the format in printf(), appreciate it for give some example of printf() for long int. I use "%LX", but still cannot.

[Haplo]

Did you try the setup_adc(ADC_CLOCK_DIV_32); ?
As others have pointed to you, according to the datasheet, the ADC clock should be set so it would guarantee a minimum of 19.2us for the conversion to complete. Your current setting is giving it less than 4us.

And also, what is the impedance on your analog pin? According to the datasheet, The maximum recommended impedance for analog sources is 10 kΩ.

[Ttelmah]

[Guest]

sorry, for my late.
So:

1. What voltage are you using for Vdd on your PIC ? (3.3v, 5v, etc. ?)

VDD = 3V


2. What is the voltage level at the A/D input pin ?
(Measure this with a voltmeter or oscilloscope).

VINA/D=0.783V

3. What value do you expect to get from the read_adc() function ?

With ICD2 i get 0d273 (correct) but with ice2000 i get 0d159 (wrong)

4. What is the actual value you get ?

see point 3.

Besides, another problem is the type float. The variables float don't return the value update but strange value.

Thanks

[hydrogene]

Hi,
I already saw this problem last month. I only forgot to put : setup_adc_ports(ALL_ANALOG).

Here my lines :
setup_port_a(ALL_ANALOG);
setup_adc_ports(ALL_ANALOG);
setup_adc(ADC_CLOCK_INTERNAL);


It's supose to work like this

David

[Guest]

Hi David,
thanks for your suggestion but it doesn't work.
About the type float can i help me?

Thanks in advance
Tony

[hydrogene]

I don't know what you mean by float type.

read_adc return a 10 bits integer. with this, you must do this :

Float = value * 5 / 1024;

It's only what I understand... if it's not that, you can explain more please

David