PIC32MX: I2C Communication between PIC32s

Original Assignment

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Your assignment is to create code that allows two PIC32s to communicate via I2C.

Overview

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Circuit

Include a schematic and give any part numbers. A photo of your circuit is OK, but not as a replacement for a schematic.

Code

(code description here)

Master Code

/*******************************************************
 * I2C_Master.c: Master code for I2C communication.	*
 * 	Both PICS use I2C1 module to send/ recieve data.*
 *	The master sends different values to a slave,   *
 *	which uses an interrupt to respond accordingly.	*
 *							*
 * Hardware: 2 PIC32MX460F512L PICs on NU32 boards	*
 *******************************************************
 * Thomas Peterson, James Rein, Eric West		*
 * ME333 Winter 2010					*
 * File Created: 	05-FEB-2010			*
 * Last Modified: 	14-FEB-2010			*
 *******************************************************/

#include "HardwareProfile.h"
#include <plib.h>

#define SYSCLK	(80000000)
#define PBCLK  (SYSCLK)
#pragma config FPBDIV = DIV_1				//Sets PBCLK to SYSCLK

#define Fsck	50000      					//Frequency of (I2C) serial clock
 
#define Nop() asm( "nop" )                 //No-operation; asm stands for assembly, using an assembly command in C.  Cool!

#define INPUT_A9       PORTAbits.RA9
#define INPUT_A10       PORTAbits.RA10


//function declaration for sending data and selecting slave address
void SendData(int,unsigned int);
void Delayms( unsigned t);

/*
This function is a delay function, causing the program to wait for approximately 4 * cnt cycles
1 cycle is 1/SYSCLK seconds.
*/
void i2c_wait(unsigned int cnt)
{
	while(--cnt)
	{
		Nop();
		Nop();
	}
}


/* Main function */
int main(void)
{
    // Configure the proper PB frequency and the number of wait states.
	SYSTEMConfigPerformance(SYS_FREQ);

	// Set all analog pins to be digital I/O
   	AD1PCFG = 0xFFFF;

	//Setup TRIS bits for switches and I2C pins
	TRISAbits.TRISA9=1;
	TRISAbits.TRISA10=1;
	TRISAbits.TRISA14=0;
	TRISAbits.TRISA15=0;

	//Initialize all of the LED pins
	mInitAllLEDs();


	unsigned char SlaveAddress;   //Slave address variable to tell the master where to send the data.  
                                     //Will be re-assigned for multiple slaves.

	//Enable I2C channel and set the baud rate to BRG_VAL)
	OpenI2C1( I2C_EN, BRG_VAL );

	int rcv;			//For received data

	//While loop to test LED functionality 
	while(1) {
		if (INPUT_A9 == 0) {				//First button pressed
			while(INPUT_A9 == 0) { Nop(); }	//Wait for release
			mLED_2_Toggle();			//Toggle LED2
			SendData(0xAA,0x40);  			//Sends hex data 0xAA to slave address 0x40
			rcv = RcvData(0x40);			//Receives data from address 0x40				
			Delayms(100);
		}
		if (INPUT_A10 == 0) {				//Second button pressed
			while(INPUT_A10 == 0) { Nop(); }
			mLED_1_Toggle();			//Toggle LED1
			SendData(0x23,0x40);    		//Sends hex data 0xAA to slave address 0x40
			rcv = RcvData(0x40);		        //Receives data from address 0x40			
			Delayms(100);		
		}
	}//while loop ending

	return 0;
}  //ending main 


/*****************************************************
 * RcvData(unsigned int address)		     *
 *					  	     *
 * Gets a byte of data from I2C slave device at      *
 *  ADDRESS.					     *
 *						     *
 * Returns: Received data			     *
 ****************************************************/
int RcvData(unsigned int address) {
	StartI2C1();				//Send line start condition
	IdleI2C1();			        //Wait to complete
	MasterWriteI2C1((address << 1) | 1);	//Write out slave address OR 1 (read command)
	IdleI2C1();				//Wait to complete
	int rcv = MasterReadI2C1();		//Read in a value
	StopI2C1();				//Send line stop condition
	IdleI2C1();				//Wait co complete
	return rcv;				//Return read value
}



/***************************************************
 * SendData(int data, unsigned int address)        *
 *						    *
 * Sends a byte of data (DATA) over the I2C line   *
 *	to I2C address ADDRESS			    *
 *						    *
 * Returns: nothing				    *
 ***************************************************/
void SendData (int data, unsigned int address){
	StartI2C1();	        //Send the Start Bit
	IdleI2C1();		//Wait to complete

	MasterWriteI2C1((address << 1) | 0);  //Sends the slave address over the I2C line.  This must happen first so the 
                                             //proper slave is selected to receive data.
	IdleI2C1();	        //Wait to complete

	MasterWriteI2C1(data);  //Sends data byte over I2C line
	IdleI2C1();		//Wait to complete

	StopI2C1();	        //Send the Stop condition
	IdleI2C1();	        //Wait to complete

} //end function



void Delayms( unsigned t)
// This uses Timer 1, can be changed to another timer. Assumes FPB = SYS_FREQ
{
    OpenTimer1(T1_ON | T1_PS_1_256, 0xFFFF);
    while (t--)
    {  // t x 1ms loop
        WriteTimer1(0);
        while (ReadTimer1() < SYS_FREQ/256/1000);
	}
	CloseTimer1();
} // Delayms

Slave Code

/***********************************************************************
 * PIC32 I2C Slave Code                
 ***********************************************************************/

#include "GenericTypeDefs.h"
#include "Compiler.h"
#include "HardwareProfile.h"
#include <plib.h>

#define SYSCLK	(80000000)
#define PBCLK  (SYSCLK)

#define Fsck	50000
#define BRG_VAL 	((PBCLK/2/Fsck)-2)

// this is the modules Slave Address
#define SLAVE_ADDRESS 0x40

// volatile variables to hold the switch and led states
volatile unsigned char dataRead = 0;

///////////////////////////////////////////////////////////////////
//
//	InitI2C
//
// 	Perform initialisation of the I2C module to operate as a slave
//
///////////////////////////////////////////////////////////////////
void InitI2C(void)
{
	unsigned char temp;
	
	// Enable the I2C module with clock stretching enabled
	OpenI2C1(I2C_ON | I2C_7BIT_ADD | I2C_STR_EN, BRG_VAL);
	
	// set the address of the slave module, address matching is with bits
	// 7:1 of the message compared with bits 6:0 of the ADD SFR so we
	// need to shift the desired address 1 bit. 
	I2C1ADD = SLAVE_ADDRESS; // >> 1;
	I2C1MSK = 0;
	
	// configure the interrupt priority for the I2C peripheral
	mI2C1SetIntPriority(I2C_INT_PRI_3 | I2C_INT_SLAVE);

	// clear pending interrupts and enable I2C interrupts
	mI2C1SClearIntFlag();
	EnableIntSI2C1;
}

///////////////////////////////////////////////////////////////////
//
//	main routine
// 
//	This code example demonstrates using the PIC32 as an I2C slave
//	
//
///////////////////////////////////////////////////////////////////
int main (void)
{
	// set for 80MHz operation
	SYSTEMConfigPerformance(SYSCLK);
	// set the Pbus to be 40000000
	mOSCSetPBDIV(OSC_PB_DIV_2);
	// disable the JTAG port
	mJTAGPortEnable(0);
	// enable interrupts
	INTEnableSystemMultiVectoredInt();
	
	InitI2C();
	mInitAllLEDs();

	// main loop
	while (1) {
		/* If global variable "dataRead" is set high during interrupt, turn on all LEDs */
		if (dataRead == 0xAA)
		{
			mLED_0_On();
			mLED_1_On();
			mLED_2_On();			
			mLED_3_On();			
			
		}
	}
}

///////////////////////////////////////////////////////////////////
//
// Slave I2C interrupt handler
// This handler is called when a qualifying I2C events occurs
// this means that as well as Slave events 
// Master and Bus Collision events will also trigger this handler.
//
///////////////////////////////////////////////////////////////////
void __ISR(_I2C_1_VECTOR, ipl3) _SlaveI2CHandler(void)
{
	mLED_1_On();
	unsigned char temp;
	static unsigned int dIndex;
	
	// check for MASTER and Bus events and respond accordingly
	if (IFS0bits.I2C1MIF == 1) {
		mI2C1MClearIntFlag();
		return;		
	}
	if (IFS0bits.I2C1BIF == 1) {
		mI2C1BClearIntFlag();
		return;
	}
	mLED_1_Off();
	mLED_2_On();
	
	// handle the incoming message
	if ((I2C1STATbits.R_W == 0) && (I2C1STATbits.D_A == 0)) {
		// R/W bit = 0 --> indicates data transfer is input to slave
		// D/A bit = 0 --> indicates last byte was address  
		
		// reset any state variables needed by a message sequence	
		// perform a dummy read of the address
		temp = SlaveReadI2C1();
		
		mLED_3_On();
		mLED_2_Off();
		// release the clock to restart I2C
		I2C1CONbits.SCLREL = 1; // release the clock

	} else if ((I2C1STATbits.R_W == 0) && (I2C1STATbits.D_A == 1)) {
		// R/W bit = 0 --> indicates data transfer is input to slave
		// D/A bit = 1 --> indicates last byte was data
		
		mLED_3_On();
		mLED_2_On();
		// writing data to our module, just store it in adcSample
		dataRead = SlaveReadI2C1();
		
		// release the clock to restart I2C
		I2C1CONbits.SCLREL = 1; // release clock stretch bit

	} else if ((I2C1STATbits.R_W == 1) && (I2C1STATbits.D_A == 0)) {
		// R/W bit = 1 --> indicates data transfer is output from slave
		// D/A bit = 1 --> indicates last byte was address
		mLED_0_On();
		mLED_2_Off();
		// read of the slave device, read the address 
		temp = SlaveReadI2C1();
		dIndex = 0;
		SlaveWriteI2C1(dataRead);
	} else if ((I2C1STATbits.R_W == 1) && (I2C1STATbits.D_A == 1)) {
		// R/W bit = 1 --> indicates data transfer is input to slave
		// D/A bit = 1 --> indicates last byte was data
		mLED_0_On();
		mLED_2_On();
		
		// output the data until the MASTER terminates the
		// transfer with a NACK, continuing reads return 0
		if (dIndex == 0) {
			SlaveWriteI2C1(dataRead);
			dIndex++;
		} else
			SlaveWriteI2C1(0);
	}
	
	// finally clear the slave interrupt flag
	mI2C1SClearIntFlag();		
}