I2C on PIC microcontroller

Question

I am trying to to use I2C to communicate with a sensor. I have a 2.2k pull-up resistors to a 3.3V supply for my SDA/SCL. The microcontroller I am using is a PIC16F18324. In my tests I do not have the slave connected. Apparently, my SDA line is being pulled low by the microcontroller and I am unable to transmit any data through the lines.

Here are two references I have been using: https://www.8051projects.net/wiki/I2C_Implementation_on_PIC https://electrosome.com/i2c-pic-microcontroller-mplab-xc8/

#include <xc.h>
#include <stdint.h>
#include <stdbool.h>
#define _XTAL_FREQ 4000000 //4 Mhz
uint16_t count = 0;
void I2C_Master_Init(const unsigned long c)
{
 TRISC = 1; // Enable TrisC RC0-SCL/RC1-SDA
 SSP1STAT |= 0b10000000;
 SSP1CON1 = 0b00101000; //Configure for master mode
 SSP1CON2 = 0b00000000;
 SSPADD = (_XTAL_FREQ/(4*c))-1;
}
void I2C_Master_Wait()
{
 while ((SSP1STAT & 0b00000100) || (SSP1CON2 & 0x00011111)); //Check if busy
}
void I2C_Master_Start()
{
 //I2C_Master_Wait(); 
 SEN = 1; //Initiate start condition
 while(SEN);
}
void I2C_Master_RepeatedStart()
{
 //I2C_Master_Wait();
 RSEN = 1; //Initiate repeated start condition
 while(RSEN);
}
void I2C_Master_Stop()
{
 //I2C_Master_Wait();
 PEN = 1; //Initiate stop condition
 while(PEN);
}
void I2C_Master_Write(unsigned data)
{
 SSP1BUF = data; //Write data to SSP1BUF
 while(BF);
 I2C_Master_Wait();
}
unsigned short I2C_Master_Read(unsigned short a)
{
 unsigned short temp;
 RCEN = 1;
 while(!BF);
 temp = SSP1BUF; //Read data from SSP1BUF
 I2C_Master_Wait();
 ACKDT = (a)?0:1; //Acknowledge bit
 ACKEN = 1; //Acknowledge sequence
 return temp;
}
void main(void)
{ 
 OSCCON1 = 0x60; // HFINTOSC Higher, faster
 OSCFRQ = 0x03; // HFFRQ 4_MHz; Enables 4Mhz for Register HFINTOSC
 I2C_Master_Init(100000); //Initialize I2C Master w/ 100Khz Clock
 while (1)
 {
 I2C_Master_Start(); //Start condition
 I2C_Master_Write(0x05); //7 bit address + Write
 I2C_Master_Write(0xFF); //Write data
 I2C_Master_Stop(); //Stop condition
 __delay_ms(200);
 }
}

• Roger Rowland: TRISC = 1 only sets RC0 as a tri-stated input. Try changing that to TRISC = 0b11 instead.
• Kevin Ly: Ah whoops I messed that up. That actually fixed my pull down problem. However, I still cannot see any being transmitted on the line.

Answer 1

I2C_Master_Write(0x05); //7 bit address + Write

Check this line , instead of writing the value you are reading the value.

Answer 2

The problem is on the line ACKDT = (a)?0:1;. Try ACKDT = 1; instead.

/*********************************************************************/
void I2C_Master_Wait(void)
 {
 while ((SSPSTAT & 0x04) || (SSPCON2 & 0x1F));
 }
/*********************************************************************/
void I2C_Master_Start(void)
 {
 I2C_Master_Wait();
 SEN = 1;
 }
/*******************************************************************/
void I2C_Master_Stop(void)
 {
 I2C_Master_Wait();
 PEN = 1;
 }
/******************************************************************/
unsigned unint8 I2C_Master_Read(unsigned short a)
 {
 unsigned unint8 temp;
 I2C_Master_Wait();
 RCEN = 1;
 I2C_Master_Wait();
 temp = SSPBUF;
 I2C_Master_Wait();
 //ACKDT = (a)?0:1; //This occurs problem
 ACKDT = 1; //SHOULD TRY THIS
 ACKEN = 1;
 return temp;
 }

Answer 3

Here is another problem:

TRISC = 1; // Enable TrisC RC0-SCL/RC1-SDA

Only RC0 is an input. Try this:

TRISC = 0x03; // Enable TrisC RC0-SCL/RC1-SDA

And please remember to switch the port to digital:

ANSELC = 0x00; // Enable TrisC RC0-SCL/RC1-SDA