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roivas
Joined: 28 Jan 2009
Posts: 5
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| ADC question --PIC16F877a, PICDEM 2+ |
 Posted: Fri Feb 20, 2009 7:43 pm |
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I am trying to integrate 2 RTD's onto a PICDEM 2+ (Rev. 2002 --Red board) with a 16f877a. I am using the flex_lcd.c LCD driver which uses pins A1:A3, and have a question about configuring the adc using "setup_adc_ports()". All but one of the defines from the header file use at least one of the pins used in the LCD driver. Is there a way to select individual pins and configure them for adc without selecting all the others? I would really like to configure E0:E1 only, but so far I have had no luck with this. I have tried changing the pins' status after using the "setup_adc_ports using set_tris_a, but it still makes the LCD inoperable. I would like to avoid having to multiplex the signals into A0 if possible. Has anyone else had any experience with this sort of thing?
Portions of my code:
| Code: | #include <16F877a.H>
#device adc=10//designates 10-bit a/d conversion
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#include "flex_lcd.c"//LCD driver
#include "keypad_init.c"//Keypad driver
#include "menu.c"//Menus
void main()
{
int16 adc_value_faucet,adc_value_tub;
lcd_init();
kbd_init();
setup_adc_ports(AN0);//Tells pin A0 that it will recieve analog input
//setup_adc_ports(AN0_AN1_AN2_AN3_AN4);
//set_tris_a(0x0e);
setup_adc(ADC_CLOCK_DIV_8);
set_adc_channel(0);//0=RA0/AN0;5=RE0/AN5;6=RE1/AN6
delay_us(20);
//input(PIN_A1);input(PIN_A2);input(PIN_A3);
set_adc_channel(0);//0=RA0/AN0;5=RE0/AN5;6=RE1/AN6**Currently Reads RA0**will be RE0
delay_us(20);
adc_value_faucet = read_adc();//gets a number from the adc
set_adc_channel(6);//READS RE1****this is the part I want to work
delay_us(20);
adc_value_tub=read_adc();
....other code
} |
All of my code works using only A0. I can post the complete code if required, but it is quite long. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Feb 20, 2009 11:10 pm |
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| Quote: | | Is there a way to select individual pins and configure them for adc without selecting all the others? |
Not with this PIC. The allowable combinations of Analog pins are listed in
the 16F877A.h file. You can't select them individually. Look in this
section:
| Quote: | | // Constants used in SETUP_ADC_PORTS() are: |
Here's the file location:
| Quote: | | c:\Program Files\picc\Devices\16f877a.h |
If you want to select individual pins for Analog input, you can do this if
buy a 16F887 chip. It's basically compatible with the 16F877A, but has
several improvements. They should put it in the PicDem2-Plus package
instead of the older PIC.
You can order free samples from Microchip:
http://www.microchip.com/samples/Default.aspx?testCookies=true
If you're in or near the U.S., you can buy it for $2.64 USD with no
minimum order charge (DIP-40 package):
http://www.mouser.com/Search/Refine.aspx?Keyword=579-PIC16F887-I%2fP
There are many other companies worldwide that sell the 16F887. |
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roivas
Joined: 28 Jan 2009
Posts: 5
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| Posted: Sat Feb 21, 2009 7:57 am |
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Thanks for the reply. 
I did notice the constants for the setups were groups and that this mirrored the info on the data sheet. I was hoping that there was a way to work around it. I also noticed that the 18F chip that comes with the board has the same adc port setup condition. This would not be a problem on the newer board, where the LCD control lines are on Port D.
The good thing is... the chips are pretty cheap  |
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