10 years, 8 months ago.

PIC16 to I2C Communication Issues

Hi,

I'm having a few issues with communication between a PIC16F877A and an MBED.

I will post some code later, but in the meantime I have a few questions;

Pull-ups, will the value effect the operation? I currently have tried 10k and 4.7k. They are tied to a 4.5v line, so I wasn't sure if I should be using a 3.3v supply as the MBED generally uses 3.3v?

Also, addressing, I understand the 7bit/8bit addressing, my PIC starts an I2C and reports (via logic analyser) that it has sent the address and received an ACK from the MBED. However in the MBED code, the slave.recieve() returns 0, which is Not Addressed. I am currently using an address of 0x00 to keep it simple. I wasn't sure how the PIC was getting an ACK, unless the line is taking too long to return high?

Do I also need any capacitors to help stabilise any lines?

Thanks James

Here is a screen shot of the Logic Analyser results from the PIC with the MBED attached, for some reason the MBED fails to ACK.

/media/uploads/jamesjnr/screen_shot_2014-04-08_at_20.09.51.png

#include <mbed.h>
I2CSlave slave(p28,p27); //Configure I2C slave
DigitalOut red_led(LED1); //red led
Serial pc(USBTX,USBRX);

int main() {
   
   slave.address(0x7E);
       while (1) { 
       int i;     

            //test for I2C, and act accordingly
           i = slave.receive();
           //pc.printf("Slave value  :    %d \n\r" ,i);
           if (i == 3){ 
           //pc.printf("Slave addressed  :    %d \n\r" ,i);
               red_led=1;
        
           }
       }
}