I2C Between Two 18F4431

[Carl Eldredge]

Hi,
I'm a neophyte in programming. Could someone please look at this code and tell me if they see anything wrong. I can't get it to work properly. A few times I was able to write to the slave, but it would never respond.

Thanks a lot.

Code for the Master:

#include <18F4431>
#fuses HS,NOPROTECT,BROWNOUT,NOWDT,BORV42
#use delay(clock=10M)
#use i2c(Master, sda=PIN_C4, scl=PIN_C5, SLOW=100000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)

int ack;
//BYTE SSPADD = 24; // 100khz

////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////

void receive(int number)
{
if(!ack==0) // Acked?
{
printf(" # %x ERROR!!\n\r",number); // If not: ERROR
}
}


////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////

void read_write(void) // Write data and the read it.
{
BYTE data;

printf("Starting to write...\n\r");
delay_ms(1000);

i2c_start();
ack = i2c_write(0xa0); // Control byte (write)
receive(1);
ack = i2c_write(0x00); // Address
receive(2);
ack = i2c_write(0x42); // Write Data
receive(3);
i2c_stop(); // End


printf("If there were no errors, the write was successful.\n\r");
printf("Short delay...\n\r");

delay_ms(1000); // Allow 94 ms extra for safety

///////////////////////////READING//////////////////////////////////////////////

printf("Read is beginning...\n\r");
delay_ms(1000);
i2c_start();
ack=i2c_write(0xa0);
receive(1);
ack=i2c_write(0x00);
receive(2);
i2c_start();
ack=i2c_write(0xa1);
receive(3);
data = i2c_read(0);
i2c_stop();
printf("Read complete\n\r");

printf("Data: /%c/ \n\r",data);


}
///////////////////////////////////////////////////////////////////////////////
//===================================
void main()
{
while(true) // Loop forever
{
read_write();
printf("Wait for 10 seconds\n\r");
delay_ms(10000);
}

}



Code for Slave:

#include <18F4431.h>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, BORV42, PUT, NOLVP
#use delay(clock=4M)
#use i2c(SLAVE, SDA=PIN_C4, SCL=PIN_C5, address=0xa0, SLOW=100000, FORCE_HW)

BYTE address, buffer[0x10];
//BYTE SSPADD = 0x09; // Set baud rate to 100khz


///////////////////////////////////////////////////////////////////////////////

#INT_SSP
void ssp_interupt()
{
BYTE incoming, state;

output_high(PIN_B2); // Turn on LED 3

state = i2c_isr_state();

if(state <0x80> 0x80)
output_high(PIN_B3); // Turn on LED 4
}

////////////////////////////////////////////////////////////////////////////////


void main()
{
enable_interrupts(GLOBAL);
enable_interrupts(INT_SSP);

set_tris_c(0b11111111);

while(1) // Forever
{
if(buffer[address]==0x42) // If I2C worked
{
output_high(PIN_B1); // Flash LED 2
delay_ms(100);
output_low(PIN_B1);
delay_ms(100);


output_low(PIN_B0); // Turn off LED 1
}

else
{
output_high(PIN_B0); // Turn on LED 1

}

}
}

[PCM programmer]

1. The slave should be running at 8 MHz minimum.
2. You access the i2c receive buffer in main(), but you don't set
the index variable to a specific value.

[Carl Eldredge]

Thanks. I actually got it working by lowering the baud rate. To speed it up, I'll get another crystal.