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I2C troubles - 2 PICs

 
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erik006



Joined: 05 Jan 2008
Posts: 10

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I2C troubles - 2 PICs
PostPosted: Sat Mar 01, 2008 11:02 pm     Reply with quote
I'm trying to get two PICs the communicate over i2c. For now, I'm using 2 18F2431 PICs to test out the i2c routines.

The trouble is: it's just not working properly. Although at first, using the EX_SLAVE example from CCS, it would work semi-decently. (it would sometimes send back what I sent it).

I'm using master code suggested by PCM programmer, and slave code from the EX_SLAVE example.

Master code:
Code:

   int8 data;
i2c_start();
i2c_write(0xA0);
i2c_write(0x00);
i2c_write('B');
i2c_stop();

// Read from the slave board and display the data.
i2c_start();
i2c_write(0xA0);
i2c_write(0x00);
i2c_start();
i2c_write(0xA1);
data = i2c_read(0);
i2c_stop();
printf("read %c \n\r", data);


One PIC is running on an internal oscillator (8MHz) and since it's on a PCB it's sort of tough to change that right now. For the other PIC i've tried using the internal osc, and crystal with the following values: 8Mhz, 10Mhz, 12Mhz,25Mhz. All with the proper delay values.

I've tried using 2.2K & 370 Ohms pull up resistors. I've tried using force_hw, & SLOW options.

I tried turning leds on in the interrupt routine of the slave & master, which seemed to work. Somehow though, I don't receive the proper character.

Compiler version: 4.057.

Any ideas?

Thanks,

Erik
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sat Mar 01, 2008 11:34 pm     Reply with quote
1. Post the full master program. I mean show the #include, #fuses, and
#use statements. Show the main(), and the braces, etc.

2. Post the #include, #fuses, and #use statements of the Ex_Slave.c
program. In other words, post only the part of Ex_Slave.c that you
modified, which will be those first few lines.

3. Do you have a ground connection between the two boards ?

4. Are both boards running at 5v ?

5. When you use 2.2K pull-ups, and send the letter 'B', what do
you get back ? If it's some strange character, then change the %c
into a %x in the printf statement. Then post the value that you get back.
(Don't test it with 370 ohm pullups. That's way too low).
erik006



Joined: 05 Jan 2008
Posts: 10

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PostPosted: Sun Mar 02, 2008 8:09 am     Reply with quote
Here's the master code:
Code:
#include <18f2431.h>
#fuses HS, NOWDT,NOPROTECT,NOLVP
#use delay(clock=8000000)
#use i2c(MASTER, SDA=PIN_C4, SCL=PIN_C5)
#use RS232(BAUD =57600, XMIT=pin_c6, RCV=pin_c7,)


void main()
{
   // Write the letter 'B' to the slave board.
   int8 data;
   i2c_start();
   i2c_write(0xA0);
   i2c_write(0x00);
   i2c_write('B');
   i2c_stop();

   // Read from the slave board and display the data.
   i2c_start();
   i2c_write(0xA0); 
   i2c_write(0x00);
   i2c_start();
   i2c_write(0xA1);
   data = i2c_read(0);
   i2c_stop();
   printf("read %c \n\r", data);
   
   while(TRUE){}
}


Slave fuses:
Code:
#elif defined(__PCH__)
#include <18F2431.h>
#fuses RC_IO,NOWDT,NOPROTECT,NOLVP
#use delay(clock=8000000)
//#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#endif

#use i2c(SLAVE, SDA=PIN_C4, SCL=PIN_C5, address=0xa0)


The master board distributes 5V power to the slave board, so the grounds are connected. At first I got a strange character back, when I changed it, I started getting an 'ff' back. When I changed it back, I still got an 'ff' back.
Hope that helps,

Erik
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun Mar 02, 2008 11:24 am     Reply with quote
Quote:
I started getting an 'ff' back

FF is what you get when the slave is dead. When you just have pull-ups
on the bus and there's no slave, you will get FF back.

Quote:

#include <18F2431.h>
#fuses RC_IO,NOWDT,NOPROTECT,NOLVP
#use delay(clock=8000000)
//#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#use i2c(SLAVE, SDA=PIN_C4, SCL=PIN_C5, address=0xa0)

The RC_IO fuse is for an external oscillator circuit that consists of
a resistor and a capacitor. I don't think you have those, so your
PIC is probably not even running. To use the internal oscillator,
you should use the INTRC_IO fuse.
erik006



Joined: 05 Jan 2008
Posts: 10

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yeah...
PostPosted: Sun Mar 02, 2008 2:49 pm     Reply with quote
Thanks PCM programmer, that fixed it. Thanks for letting me know about the "ff" deal also, that'll definitely help me spot problems in the future.

Erik
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