Shawn,
Looks OK to me.  You do need a common ground on the Pics.  You also need 2
pullup resistors on the data and clock lines.  I would say about 10k up to
+5v would do you here.

Brian.

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Shawn Van Every
Sent: 08 November 2003 17:30
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC] I2C Troubles


Hey All,

I have been trying to implement a basic I2C demonstration between 2 PIC
16F877s using CCS PIC C.  One PIC is the master and the other the
slave.  Unfortunately I am a bit unclear about the wiring and the code.
  So, if anyone out there has the inclination, I have a couple of
questions:

First, do I need to have a common ground between the PICs?

I have tried the following master and slave code with several different
wiring configurations but none seems to work, any ideas?

MASTER:
#include <16F877.h>
#fuses XT,NOWDT,NOPROTECT,NOLVP,PUT

/* Delay for 4 mhz crystal */
#use delay (clock=4000000)

/* Setup RS232 */
#use rs232(baud=9600, xmit=PIN_D4,rcv=PIN_D5, INVERT)

/* Setup I2C */
#use I2C(MASTER, sda=PIN_C4, scl=PIN_C3, SLOW)

main()
{
    char send_char = 65;
    int8 i2c_command = 66;

    while (true)
    {
       delay_ms(100);
       putc(send_char);
       delay_ms(100);
       putc(send_char+1);
       delay_ms(100);

       /* Master */
       i2c_start();             // Start condition
       i2c_write(0xa0); // Device address
       i2c_write(i2c_command);  // Write Command
       i2c_stop();              // Stop condition

    }
}


SLAVE:
#include <16F877.h>
#fuses XT,NOWDT,NOPROTECT,NOLVP,PUT

/* Delay for 4 mhz crystal */
#use delay (clock=4000000)

/* Setup RS232 */
#use rs232(baud=9600, xmit=PIN_D4,rcv=PIN_D5, INVERT)

/* Setup I2C */
#use i2c(SLAVE, SDA=PIN_C4, SCL=PIN_C3, address=0xa0, SLOW, FORCE_HW)

#INT_SSP
void ssp_interupt ()
{
    byte incoming;
    incoming = i2c_read();
    putc(incoming);
}


main()
{
    char send_char = 65;
    int received_char = 0;
    int i2c_received;

    while (true)
    {
       delay_ms(100);
       putc(send_char);


       enable_interrupts(GLOBAL);
       enable_interrupts(INT_SSP);

       /* Slave */
       ////i2c_start();
       ////i2c_write(0xa1);
       //i2c_received = i2c_read(1);
       ////i2c_stop();

       //putc(i2c_received);
    }
}

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