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12f675 ADC

 
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info@ckmintech.com



Joined: 16 May 2006
Posts: 39

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12f675 ADC
PostPosted: Sun Mar 15, 2009 9:17 am     Reply with quote

I need to have a program to read a ADC value from AN1. The following is part of my program and it works.
Code:

#include <12f675.h>
#device adc=8

....

main()
{
   int advValue;
   setup_adc_ports(sAN1|VSS_VDD);
   setup_adc(ADC_CLOCK_INTERNAL);
   set_adc_channel(1);

    .....

   delay_us(10);
   adcValue=read_adc();

}

The adcValue read is around 100 (this is correct)

I need to implement a software RS232 without MAX232 chip and added
Code:
#use rs232(baud=9600,parity=N,xmit=PIN_A4,rcv=PIN_A2,bits=8, INVERT, stream=RS232IN)

after #device adc = 8
When I hook up the RS232 connection, the adcValue changed to 18
It seems that it is reporting the value is not in the range VSS_VDD.
I added
Code:

   setup_comparator(NC_NC_NC_NC);
   setup_vref( FALSE );

but the result is the same.
Any idea how to correct the problem?

Rgds.
PCM programmer



Joined: 06 Sep 2003
Posts: 18125

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PostPosted: Sun Mar 15, 2009 1:00 pm     Reply with quote

Post a complete test program. Take the code that you posted, and
add the #fuses, #use delay(), and #use rs232() statements to it.
Add a printf statement that displays the ADC value.
Add a while(1); statement at the end of the program.

Add a few lines of code to make it into a complete test program
that is compilable.

Post your compiler version.
info@ckmintech.com



Joined: 16 May 2006
Posts: 39

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PostPosted: Sun Mar 15, 2009 6:21 pm     Reply with quote

Code:
#include <12f675.h>
#device adc=8

#FUSES NOWDT     
#FUSES INTRC_IO, PROTECT
#use delay(clock=4000000)

#use rs232(baud=9600,parity=N,xmit=PIN_A4,rcv=PIN_A2,bits=8, INVERT, stream=RS232IN)
#use rs2232(baud=9600,parity=N,xmit=PIN_A0,rcv=PIN_A5,bits=8,stream=outdata)

main()
{
   int   adcValue;

   setup_comparator(NC_NC_NC_NC);
   setup_vref( FALSE );
   setup_adc_ports(sAN1|VSS_VDD);
   setup_adc(ADC_CLOCK_INTERNAL);
   set_adc_channel(1);


   while (true) {
        delay_ms(1);
        adcValue=read_adc();
        fprintf(outdata,"(%d)", adcValue );
   }
}

The reading is around 20 (not correct). After I cut the connection DB9 pin 3, the value came back to normal - 100

Complier is OCH 3.249

Rgds.
PCM programmer



Joined: 06 Sep 2003
Posts: 18125

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PostPosted: Sun Mar 15, 2009 10:12 pm     Reply with quote

Quote:
I need to implement a software RS232 without MAX232 chip and added
Code:
#use rs232(baud=9600,parity=N,xmit=PIN_A4,rcv=PIN_A2,bits=8, INVERT, stream=RS232IN)

After I cut the connection DB9 pin 3, the value came back to normal - 100.

Do you have a series resistor between pin 3 of the Com1 connector
on your PC, and pin A2 on the PIC ? You need one. Normally, a 22K
ohm resistor is used with this type of direct connection. You only need
a resistor between the Tx pin of Com1 on the PC (pin 3) and the Rx pin
on the PIC. Without that resistor, you are putting -10v at 20ma
(or more) on pin A2 of the PIC. That could be the cause of your problems.
Guest








PostPosted: Mon Mar 16, 2009 2:04 am     Reply with quote

Yes. I have a 47K resistor.

Rgds.
PCM programmer



Joined: 06 Sep 2003
Posts: 18125

View user's profile Send private message

PostPosted: Mon Mar 16, 2009 2:14 am     Reply with quote

1. What is the Vdd voltage for your PIC ?

2. What are you using for a power supply for the 12F675 ? Is it a voltage
regulator ?

3. Do you have a pull-up resistor on the MCLR pin ? What value is it ?

4. Why do you have the PROTECT fuse enabled for this project ?
Guest








PostPosted: Mon Mar 16, 2009 7:15 am     Reply with quote

1. Vdd is +5V
2. The power is stealed from Pin 4 and Pin 7 of the RS232 by using 1N4148 diode as an input for 78L05 regulator. The output of the 78L05 regulator will power up the circuit
3. a 10K pullup for MCLR
4. PROTECT is our my standard fuse

Rgds.
PCM programmer



Joined: 06 Sep 2003
Posts: 18125

View user's profile Send private message

PostPosted: Mon Mar 16, 2009 12:22 pm     Reply with quote

I can't find my 12F675 right now. If I find it later, I'll test your code.
When I test it, I will use a bench power supply, and not serial port power.
I also will use a Max232A chip instead of INVERT mode. And I will not
use the PROTECT fuse. If it doesn't work, I will install a 4 MHz crystal,
instead of the internal oscillator.

In other words, I will do whatever it takes to make it work, by using
standard methods, rather than trying to "push" every aspect of the
design.
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