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i2c strange output...any ideas

 
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keplerforever



Joined: 23 Dec 2005
Posts: 8

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i2c strange output...any ideas
PostPosted: Sun May 07, 2006 9:25 am     Reply with quote
Hi,

I'm using a pic 16F877A clocked at 19660800 Hz, and I'm trying to connect it to a CMPS03 compass (http://www.robot-electronics.co.uk/htm/cmps3doc.shtml) using I2C protocol.
I've been using 1k8 pullup resitors on SDA and SCL lines, as the documentation indiquates.
And I've been inspiring myself with the code from this thread:
http://www.ccsinfo.com/forum/viewtopic.php?t=25869&highlight=cmps03+i2c

My problem is that I cannot recieve correct values of the compass. Instead I recieve a continuous flow of zero in my RS232 terminal.
I cannot figure out what is the issue: should I modify the code , but I'm really not an expert in I2C and I cannot make it clear when I should put delays or not (I tried many different possibilities). Is my cable too long: around 15cm
I don't see what I could test more

Thanks in advance for your inputs or code to test

Olivier
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun May 07, 2006 4:12 pm     Reply with quote
The problem is that the original poster in that thread never posted
the final working driver. Also, in his driver, he doesn't do a NACK on
the last i2c read. But all sample drivers do this. So I don't think
you can trust his driver.

If I take the sample code for the CMPS03 which Devantech has posted
at this link, http://www.robot-electronics.co.uk/files/example18f452.c
and translate it to CCS, I get the following code:

Code:

#include <16F877.H>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
#use i2c(Master, SDA=PIN_C4, SCL=PIN_C3, FORCE_HW)

void read_compass(int8 *buffer)
{
i2c_start();
i2c_write(0xC0);
i2c_write(0x00);
i2c_start();
i2c_write(0xC1);
buffer[0] = i2c_read();      
buffer[1] = i2c_read();      
buffer[2] = i2c_read();      
buffer[3] = i2c_read(0);
i2c_stop();
}

//============================
void main()
{
int8 compass[4];
int8 version;
int8 bearingB;
int16 bearingW;

while(1)
  {
   read_compass(compass);
   version  = compass[0];
   bearingB = compass[1];
   bearingW = ((int16)compass[2] << 8) + (int16)compass[3];
       
   printf("Version = %u\n\r", version);
   printf("bearingB = %u\n\r", bearingB);
   printf("bearingW = %lu\n\r", bearingW);
   printf("\n\r");
   delay_ms(1000);
  }

}
keplerforever



Joined: 23 Dec 2005
Posts: 8

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PostPosted: Mon May 08, 2006 6:41 am     Reply with quote
great!!!
The code is working perfectly.
Thank you very much, this is a relief for me, since I have always been a bit traumatized with i2c protocol
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