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Problem with serial output on 12F675

 
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John Morley



Joined: 09 Aug 2004
Posts: 97

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Problem with serial output on 12F675
PostPosted: Fri Jun 24, 2011 1:38 pm     Reply with quote
Hi All,

I'm having a problem sending serial data from a 12F675. This design uses two A/D inputs to measure the output of a couple of sensors, and then controls a warning lamp connected to an output pin. There is also a pin assigned to send diagnostic messages for troubleshooting/development purposes.

Everything is basically working OK, but my diagnostic messages are not printing correctly. I have a stripped down version of the code that shows the problem:

Code:


#include <12F675.h>
#device ADC=10
#fuses INTRC_IO, NOWDT, NOBROWNOUT, NOPROTECT, NOPUT, MCLR

// Here we configure the internal 4 MHz oscillator....
#use delay(clock=4000000)

#define Range_Input PIN_A3
#define Current_Input PIN_A2
#define Lamp_Output PIN_A5
#define Data_Output PIN_A0

// Here we configure the diagnostic serial LCD module....
#use rs232(baud=9600, xmit=Data_Output, stream = LCD)

void Blink_LED(int8 NumBlinks)
{
   int8 iIndex;

   for (iIndex = 1 ; iIndex <= NumBlinks ; iIndex++)
   {
      output_high(Lamp_Output);
      delay_ms(350);
      output_low(Lamp_Output);
      delay_ms(350);
   }
}

void main()
{
   int16 Value;
   int1 bIs28V;

   // Here we turn off unused peripherals....
   setup_timer_1(T1_Disabled);
   setup_comparator(NC_NC_NC_NC);
      setup_vref( FALSE );

   //Here we set the initial state of the lamp output
   output_low(Lamp_Output);

   // Here we configure the A/D converter module....
   // Range Sensing will be on pin 'AN3' and Current Sensing will be on pin 'AN2'....
   setup_adc_ports(sAN2 | sAN3 | VSS_VDD);
   setup_adc(ADC_CLOCK_INTERNAL );

   set_adc_channel(Range_Input);
   delay_us(10);                     // Delay to allow the channel to be acquired
   Value=read_adc();

   if (Value > 600)
   {
      Blink_LED(6);
      bIs28V = True;
   }
   else
   {
      Blink_LED(3);
      bIs28V = False;
   }
   
   // Here we have some basic diagnostic printing....
   fprintf(LCD, "Range: %lu\n\r", Value);
   fprintf(LCD, "Is28V: %u", bIs28V);
   fprintf(LCD, "\n\r");

   while(1);   //end here

}



When I run this code, I see the following printed to a Hyperterminal window:

V: 0

As you can see, most of the diagnostic message is cut off, except for the last few characters of the 2nd line.

Interestingly, if I comment out the call to the 'Blink_LED' subroutine above, it prints correctly. The problem is NOT this subroutine, however, because the issue returns if I insert any small delay directly ahead of the fprintf statements.

I assume that my serial output pin is not being configured properly, but I don't know what that issue might be. I tried to turn off all other pin functions that I'm not using.

127675 is being powered by a well filtered 7805 voltage regulator.

My compiler is v4.050

Thanks,

John
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John Morley
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri Jun 24, 2011 2:01 pm     Reply with quote
What's the manufacturer and part number of the LCD ?
Has it ever worked ?

What happens if you strip the program down, cutting out 90% of the
code and merely have a main() with a delay at the start (say, 1000 ms)
and then do a printf with a while(1) at the end ? Does it then work ?



Aside from that, here are a few other comments:
Quote:

#define Range_Input PIN_A3

set_adc_channel(Range_Input);

ADC channel numbers must be 0, 1, 2, 3, etc., not CCS pin numbers.


Quote:

#fuses INTRC_IO, NOWDT, NOBROWNOUT, NOPROTECT, NOPUT, MCLR

#define Range_Input PIN_A3

12F675 Data sheet pinout for pin 4: GP3/MCLR/VPP

If GP3 is configured as the MCLR pin, it can't be used for i/o and must
have a 10K pull-up on it. It's dedicated to being an MCLR (reset) pin only.
In fact, is it possible that you're resetting the PIC with an analog signal
coming into the MCLR pin ? Remove everything from that pin except the
10K pullup.


Quote:
setup_adc(ADC_CLOCK_INTERNAL );

The 12F675 data sheets says (in the ADC section), to use this divisor
for 4 MHz operation:
Code:
ADC_CLOCK_DIV_8
John Morley



Joined: 09 Aug 2004
Posts: 97

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PostPosted: Fri Jun 24, 2011 2:59 pm     Reply with quote
Hi,

When things did not go as expected, I added a MAX232 to my circuit, and I'm now viewing the diagnostic messages on Hyperterminal. I also tried RealTerm, so it's not the terminal client that is causing the problem.

I have a 10K pull-up on MCLR, and I changed the ADC clock to "ADC_Clock_DIV_8"

I think a problem is my confusion with physical pin numbers, pin references, and analog input references? I think I've corrected that, but the problem persists.

My hardware is connected as follows:

The digital output to the lamp is on physical Pin #2
One analog input is physical pin #3
One analog input is physical pin #5 (not used in my test example)
Diagnostic data is sent to physical pin #7

The datasheet lists pins GP0 thru GP5, and the pin references in the 12F675 header file are Pin_A0 thru Pin_A5. I assume they correspond? The A/D references are 'sAN0', 'sAN1', 'sAN2', and 'sAN3'.

Here is an updated version of the code:

Code:


#include <12F675.h>
#device ADC=10
#fuses INTRC_IO, NOWDT, NOBROWNOUT, NOPROTECT, NOPUT, MCLR

// Here we configure the internal 4 MHz oscillator....
#use delay(clock=4000000)

#define Range_Input PIN_A4
#define Current_Input PIN_A2
#define Lamp_Output PIN_A5
#define Data_Output PIN_A0

// Here we configure the diagnostic serial LCD module....
#use rs232(baud=9600, xmit=Data_Output, stream = LCD)

void Blink_LED(int8 NumBlinks)
{
   int8 iIndex;

   for (iIndex = 1 ; iIndex <= NumBlinks ; iIndex++)
   {
      output_high(Lamp_Output);
      delay_ms(350);
      output_low(Lamp_Output);
      delay_ms(350);
   }
}

void main()
{
   int16 Value;
   int1 bIs28V;

   // Here we turn off unused peripherals....
   setup_timer_1(T1_Disabled);
   setup_comparator(NC_NC_NC_NC);
      setup_vref( FALSE );

   //Here we set the initial state of the lamp output
   output_low(Lamp_Output);

   // Here we configure the A/D converter module....
   // Range Sensing will be on pin 'AN3' and Current Sensing will be on pin 'AN2'....
   setup_adc_ports(sAN2 | sAN3 | VSS_VDD);
   setup_adc(ADC_CLOCK_DIV_8);

   set_adc_channel(3);
   delay_us(10);                     // Delay to allow the channel to be acquired
   Value=read_adc();

   if (Value > 600)
   {
      Blink_LED(6);
      bIs28V = True;
   }
   else
   {
      Blink_LED(3);
      bIs28V = False;
   }
   
   // Here we have some basic diagnostic printing....
   fprintf(LCD, "Range: %lu\n\r", Value);
   fprintf(LCD, "Is28V: %u", bIs28V);
   fprintf(LCD, "\n\r");

   while(1);   //end here

}


If the 'Blink_LED' routine is executed, the diagnostic message is not printed correctly. If I comment this part out, I see the message as expected with a valid A/D reading being displayed.

Thanks,

John
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John Morley
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri Jun 24, 2011 4:25 pm     Reply with quote
It works for me. I get this output on TeraTerm:
Quote:

Range: 56
Is28V: 0
Range: 127
Is28V: 0

I ran the program twice. That's why there are two sets of output.

I didn't use a MAX232. I used a direct rs232 connection, just to save time.
I took your latest program and added the INVERT parameter to the
#use rs232() statement. Then I connected pin A0 directly to the Rx pin
on the COM port connector on my PC (with a cable). Also, I connected
ground from the board to the ground pin on the COM port. The board
is a Microchip "low pin count" board. I programmed the 12F675, and
then removed the Pickit 2, and supplied power to the board from a
+5v bench power supply. The program was compiled with vs. 4.050.
I'm sure it would work just fine if I used a Max232 and didn't use the
INVERT option.

My guess is, maybe look for a solder short on your board ? Or check the
power supply voltage and stability ?
John Morley



Joined: 09 Aug 2004
Posts: 97

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PostPosted: Sun Jun 26, 2011 7:51 pm     Reply with quote
Hi pcm!

Thanks for making those tests for me!

I'm not sure whats going on, but I can reliably cause the serial output to become corrupted simply by including the Blink_LED routine. It's a handwired prototype, so it's possible that there is a short, or some crosstalk going on that is specific to this prototype. I'm going to have a PCB built now for this project, and I'll report back when I have it to let you know whether the problem is solved or not!

Thanks,

John
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John Morley
Ttelmah



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Posts: 19506

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PostPosted: Mon Jun 27, 2011 2:41 am     Reply with quote
You have got a resistor between the PIC output, and the LED?. If not you will be overloading the PIC when you 'blink' the LED, and anything could happen....

Best Wishes
John Morley



Joined: 09 Aug 2004
Posts: 97

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PostPosted: Mon Jun 27, 2011 9:21 am     Reply with quote
Hi,

The 'LED' will actually be an incandescent warning lamp in the final application, so it's being drive by a small N-channel MOSFET connected to the PIC output pin.

Thanks for the suggestion!

John
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