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moistsam
Joined: 09 Jun 2007
Posts: 7
Location: Thessaloniki, Greece
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| A/D Problem with PIC18F2431 |
 Posted: Fri Jun 22, 2007 12:04 pm |
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I write the simple code below using CCS 3.249. I am trying to vary the duration of a pulse with the Potentiometer (PWM) but this code doesn't work with PIC18F2431. I tested this code with 16F877 and 16F876 and works fine.
The problem is in the analog channel because the variable value doesn't change when i display it in an LCD. I try but i couldn't find the reason why it happens.
| Code: |
#include <18f2431.h>
#device adc=10
#fuses HS,NOWDT,NOPROTECT,NOPUT,NOCPD,NOBROWNOUT,NOLVP
#use delay(clock=20000000)
void main()
{
int16 value;
setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_4, 63, 1);
setup_adc_ports(sAN1|VSS_VDD);
setup_adc(ADC_CLOCK_INTERNAL);
set_adc_channel(1);
delay_us(20);
while(1)
{
value=read_adc();
set_pwm1_duty(value);
}
} |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jun 22, 2007 12:15 pm |
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| Change the #device adc line to specify 8-bit mode. |
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moistsam
Joined: 09 Jun 2007
Posts: 7
Location: Thessaloniki, Greece
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| Posted: Fri Jun 22, 2007 12:23 pm |
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| I made the change but the problem still exist. I see in the oscilloscope the pulse with its maximum duty cycle but i can not change it. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jun 22, 2007 12:46 pm |
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I don't have a 18F2431, but I do have a 18F4431 (a similar chip) and I
was able to make it work. I installed PCH vs. 3.249. I changed only
one line in your program -- I changed it to provide an 8-bit ADC result:
I tested it on a PicDem2-Plus board. It has a 10K trimpot on pin A0,
so I jumpered it over to pin A1, to fit your program.
When I run the program, I get a 19.5 KHz PWM waveform on pin C2.
The duty cycle varies from 0% to 100% as I turn the trimpot from one
side to the other. |
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moistsam
Joined: 09 Jun 2007
Posts: 7
Location: Thessaloniki, Greece
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| Posted: Fri Jun 22, 2007 2:00 pm |
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| I have three PIC18F2431 and i tested all of them but they don't work. They are samples from microchip. Is there any possibility for these samples to have a problem at the analog channels? I write another code which is a simple 4-bit counter and works fine. The only problem is the analog channels! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jun 22, 2007 2:17 pm |
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1. What device is supplying the analog voltage to your PIC ?
Try using a 10K trimpot.
2. What is the range of the analog voltage ?
Is it from 0v to 5v ? Measure it with a voltmeter or a scope.
3. Are you certain that you have connected the analog voltage to the
correct pin on your PIC ? On the DIP package, AN1 is on Pin 3. |
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moistsam
Joined: 09 Jun 2007
Posts: 7
Location: Thessaloniki, Greece
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| Posted: Fri Jun 22, 2007 2:29 pm |
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| Just now i checked the things that you have mentioned but the problem exist. I also have the PICDEM2 PLUS and ICD2 Programmer. I use a 10k potentiometer and i use the PICDEMs power supply. I also tested my code with the 18F4550 to see if something is going on with the 18F series but all is ok. I thing that something happens with this specific microcontrollers. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jun 22, 2007 2:54 pm |
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| Quote: | | I also have the PICDEM2 PLUS and ICD2 Programmer. I use a 10k potentiometer and i use the PICDEMs power supply. |
I made a mistake in the trimpot value. The PicDem2-Plus board
(both versions) has a 5K trimpot.
But on that board, the built-in 5K trimpot is connected to pin RA0.
Are you using that trimpot for your tests ?
You should use it. Change your code to use A/D channel 0,
as shown in bold below.
| Quote: | setup_adc_ports(sAN0 | VSS_VDD);
setup_adc(ADC_CLOCK_INTERNAL);
set_adc_channel(0); |
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moistsam
Joined: 09 Jun 2007
Posts: 7
Location: Thessaloniki, Greece
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| Posted: Fri Jun 22, 2007 3:06 pm |
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| Yes it is a 5k pot. I use an external 10k pot with A1. I don't think that this is the problem. I checked all the connections. As i said in the first post in the 28pin package i checked the 16F876 microcontroller and worked fine. |
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moistsam
Joined: 09 Jun 2007
Posts: 7
Location: Thessaloniki, Greece
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| Posted: Fri Jun 22, 2007 3:48 pm |
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| PCM programmer thank you for your help and your time. Your help was very valuable. I will find another 18F2431 and test it again. Thanks a lot. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jun 22, 2007 3:50 pm |
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I found the problem. The PicDem2-Plus board's 28-pin socket is not
intended to work with the pinout of the 18F2431. It's only intended
to be used with a PIC such as the 16F876.
The 18F2431 needs pin 7 (DIP package) to be connected to the AVdd
voltage (+5v). On the PicDem2-Plus board, this pin is "RA5" and is
not connected to anything except the PIC sockets and the header pins.
You could jumper it to +5v. But remember to remove that jumper
when you are done testing the 18F2431. |
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moistsam
Joined: 09 Jun 2007
Posts: 7
Location: Thessaloniki, Greece
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| Posted: Fri Jun 22, 2007 4:07 pm |
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Now it works!!!! Thank you again for your help. In this package i used to work only with 16F876 and my mind didn't go to this problem.
Thanks for your time!!! |
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