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Code to Read/Write 24LC256 I2C EEPROM on MSP430G2553

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Hello,

 

I've been lurking here for well over a year and finally figured I should post something.

 

I've been learning to use the USCI I2C interface on the on MSP430G2553 and came up with this code for talking to the 24LC256 chip.

 

The code implements single/multibyte read/write routines for the 24LC256 EEPROM.  

It should work on the 24LC512 without modification and on other 24LCxx family chips with minimal modification to the addressing.

 

I have probably broken numerous coding rules and best practices, there is no error checking to speak of, and nothing has timeouts. So use at your own risk.

 

I also have screen captures from the logic analyzer showing the SCL/SDA timings.  If anyone is interested, please let me know and I'll post them.

 

Comments are welcome and appreciated.

Thanks

 

Brian

//*************************************************************************************
// MSP430G2553 24LC256/512 I2C Interface
// Brian McClure NZ8D
// first.lastname@gmail.com
// July 2014
//


/********************************************************************************************/
/*    Include                                                                               */
/********************************************************************************************/
#include	"msp430g2553.h"

/********************************************************************************************/
/*    I2C Definitions                                                               	    */
/********************************************************************************************/
//I2C Port Definitions
#define   i2cAddress     0x50    //Address GPIO Address

//USCI I2C PIN Definition
#define   SDA_PIN     BIT7		//Bit 7 USCI Port 1(SDA)
#define   SCL_PIN     BIT6		//Bit 6 USCI Port 1(SCL)


/********************************************************************************************/
/*    UART Function Definitions                                                                  */
/********************************************************************************************/

void UART_puts(char * s);
void UART_outdec(long data, unsigned char ndigits);

/********************************************************************************************/
/*    I2C Function Definitions  												                */
/********************************************************************************************/
void I2C_Write_EEProm(unsigned char slave_address, unsigned int register_address, char * data, unsigned char DataLength );
void I2C_Read_EEProm(unsigned char slave_address, unsigned int memory_address, char * data, unsigned char DataLength );


/********************************************************************************************/
/*    Misc Function Definitions                                                                  */
/********************************************************************************************/
void delay_ms(unsigned int delay);			//Delay


/********************************************************************************************/
/*   Main                                                                  */
/********************************************************************************************/
void main(void) {

	WDTCTL = WDTPW + WDTHOLD;		  	// Stop WDT

	BCSCTL1 = CALBC1_16MHZ;				//set DCO to 16Mhz
	DCOCTL = CALDCO_16MHZ;				// make sure to update the Delay_ms function if the DCO is changed


	//UART Initial
	P1SEL = BIT1 + BIT2;                     // P1.1 = RX pin, P1.2=TX pin
	P1SEL2 = BIT1 + BIT2 ;                    // P1SEL and P1SEL2 = 11--- Secondary peripheral module function is selected.
	UCA0CTL1 |= UCSSEL_2;                     // SMCLK
	UCA0BR0 = 69;                             // 16MHz 230400
	UCA0BR1 = 0;                              // 16MHz 230400
	UCA0MCTL = UCBRS0;                        // Modulation UCBRSx = 1
	UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
	IE2 |= UCA0RXIE;                          // Enable USCI_A0 RX interrupt

	//USCI_I2C_Init
	P1SEL |= SDA_PIN + SCL_PIN;						// Assign I2C pins to USCI_B0
	P1SEL2|= SDA_PIN + SCL_PIN;
	UCB0CTL1 = UCSWRST;								// Enable SW reset, HOLD USCB in a reset state
	UCB0CTL0 = UCMST + UCMODE_3 + UCSYNC;			// I2C Master, MODE 3 = I2C, synchronous mode
	UCB0CTL1 = UCSSEL_2 + UCSWRST;					// Use SMCLK, keep SW reset
	UCB0BR0 = 72;									// Set I2C master speed  72 gives approx 200Khz clock at 16Mhz
	UCB0BR1 = 0;									// Set I2C master speed
	UCB0CTL1 &= ~UCSWRST;							// Clear SW reset, resume operation


	UART_puts("Starting...\r\n");		//output to UART to indicate the program is running

	__bis_SR_register(CPUOFF + GIE);        							// LPM0 with interrupts enable

		while (1){ }
}

 void UART_puts(char * s) {
 	while (*s) {
 		while (!(IFG2 & UCA0TXIFG));                // USCI_A0 TX buffer ready?
 		UCA0TXBUF = *s++;
 	}
 }


 void UART_outdec(long data, unsigned char ndigits){  	//UART_outdec modified/hacked to properly handle negative numbers.
 	unsigned char sign, s[15];			//I copied this from a TI example or the 40oh forum, but I'm not sure of the original author.
 	unsigned int i;
 	sign = 0x00;

 	if(data < 0) {
 		sign='-';
 		data = -data;
 	}
 	i = 0;

 	do {
 		s[i++] = data % 10 + '0'; //adds the value of data least sig digit to ascii value of '0'
 		if(i == ndigits) {
 			s[i++]='.';
 		}
 	} while( (data /= 10) > 0);

 	if (i < ndigits) //fixes loss of leading 0 in fractional portion when number of digits is less than length of data
 	{
 		do {
 			s[i++]='0';
 			} while (ndigits > i) ;

 		s[i++]='.';
 	}

 	if (sign == '-')  //if value is negative then include the '-' sign
 	{
 		s[i] = sign;
 	} else
 	{			//if value is positive then reduce 'i' counter by 1 to prevent the do loop from trying to output a sign character.
 		i--;
 	}

 	do {
 		while (!(IFG2 & UCA0TXIFG));
 		UCA0TXBUF = s[i];
 	} while(i--);
 }




 void delay_ms(unsigned int delay)
 {
     while (delay--)
     {
         __delay_cycles(16000);  //1ms = 1000 cycles per 1Mhz clock freq.
     }
 }


void I2C_Read_EEProm(unsigned char slave_address, unsigned int memory_address, char * data, unsigned char DataLength )
{ //Reading from a 24LCxxx series is much easier then writing.  Reading doesn't have to be done in 64 byte pages.
	/*
		 * Todo:
		 * 1. add checks to make sure write does not exceed maximum length of EEprom
		 * 2. check for valid memory_address
		 *
		 */

	int rLoop = 0;	//loop counter

	while (UCB0STAT & UCBBUSY);			//wait for USCI B0 bus to be inactive
	UCB0I2CSA = slave_address;			//set SLAVE address

	UCB0CTL1 |= UCTR + UCTXSTT;						//set USCI to be I2C TX,  send start condition
	UCB0TXBUF = (memory_address & 0x7F00) >> 8;		//transfer memory_address MSB

	while (UCB0CTL1 & UCTXSTT);						// waiting for slave address to transfer
	while ((IFG2 & UCB0TXIFG) != UCB0TXIFG);		//wait for TX IFG to clear

	UCB0TXBUF = (memory_address & 0x00FF);			//transfer memory_address LSB
	while ((IFG2 & UCB0TXIFG) != UCB0TXIFG);		//wait for TX IFG to clear

	UCB0CTL1 &= ~UCTR;  			//set USCI to be RECEIVER
	UCB0CTL1 |= UCTXSTT; 			//send restart
	while (UCB0CTL1 & UCTXSTT);		// wait until I2C STT is sent

	for (rLoop=0; rLoop<DataLength; rLoop++)	//receive loop
	{
		 while ((IFG2 & UCB0RXIFG) != UCB0RXIFG); //wait for RX buffer to have data
		    data[rLoop] = UCB0RXBUF;  //Move rvcd data of or USCI buffer. This also clears the UCB0RXIFG flag

		    if (rLoop == DataLength-2) 	//NACK and STOP must be send before the last byte is read from the buffer.
		    							//if not the CPU will read an extra byte.
		    {
		    	UCB0CTL1 |= UCTXNACK; //generate a NACK
		    	UCB0CTL1 |= UCTXSTP;  //generate a stop condition
		    }
	}


}

void I2C_Write_EEProm(unsigned char slave_address, unsigned int memory_address, char * data, unsigned char DataLength )
{
	/*
	 * Todo:
	 * 1. add checks to make sure write does not exceed maximum length of EEprom
	 * 2. check for valid memory_address
	 *
	 */


	int NumPages = (DataLength)/64 ; //Count of full 64 byte pages, 0 means the data is less than a full 64 byte page
	int PartialPageBytes = DataLength % 64;  //this is the number of bytes remaining that do not make up a full page

	int address = 0; //EEprom memory starting address, this is different from the I2C slave address
	int NP =1; //loop counter to iterate though pages of memory
	int offset = 0;
	int offsetlimit = 0;

	if (PartialPageBytes > 0)
	{
		NumPages++; //if we have left over bytes that do not make up a full page, this will add a page to handle those bytes.
	}

    __disable_interrupt(); //prevent interrupts from messing with the I2C functions

	while (UCB0STAT & UCBBUSY);		//wait for USCI B0 bus to be inactive
	    	UCB0I2CSA = slave_address;			//set SLAVE address

    for (NP=1; NP<=NumPages; NP++)
	{

		address = ((NP-1) * 64) + memory_address; //this is the full page start address

		UCB0CTL1 |= UCTR + UCTXSTT;			//set USCI to be I2C TX,  send start condition
		UCB0TXBUF = (address & 0x7F00) >> 8;		//transferring memory_address MSB

		while (UCB0CTL1 & UCTXSTT);					// waiting for slave address was transferred
		while ((IFG2 & UCB0TXIFG) != UCB0TXIFG);		//wait for TX IFG to clear

	    UCB0TXBUF = (address & 0x00FF);		//transferring memory_address LSB
   	    while ((IFG2 & UCB0TXIFG) != UCB0TXIFG);		//wait for TX IFG to clear

   	    offsetlimit = 63; 		//set the offset limit to 63

   	    if ((NP == NumPages) && (PartialPageBytes > 0))		//if we are preparing to send the last/partial page
   	    {
   	    	offsetlimit = PartialPageBytes-1;				//set the offset limit to the number of partial page bytes
   	    }
		for (offset=0; offset <=offsetlimit; offset++)
		{
			UCB0TXBUF = data[((NP-1)*64)+offset];					//send data.
			//UART_outdec(offset,0);

			while ((IFG2 & UCB0TXIFG) != UCB0TXIFG);	//wait for TX IFG to clear

		}

		UCB0CTL1 |= UCTXSTP;                    // set I2C stop condition
		while ((UCB0STAT & UCSTPIFG) == UCSTPIFG); //wait for Stop condition to be set

						//delay while the EEPROM completed its write cycle.
						//It would be better to use NACK polling here as described in the datasheet.
	    delay_ms(6); 	//24LC256 has a max page write time of 5ms, so we will wait 6ms to be sure
	}

	UART_puts("Done...\r\n");
	__enable_interrupt();

}


// -----------------------------------------------------------------------------
// Interrupt Handlers
// -----------------------------------------------------------------------------


#pragma vector=USCIAB0RX_VECTOR
__interrupt void USCI0RX_ISR(void)
{
	__bic_SR_register_on_exit(CPUOFF);        // Clear CPUOFF bit from 0(SR)

	char RxChar = 0x00; //char used to receive serial data
	RxChar = UCA0RXBUF;                    // copy the RX buffer into RxChar

	char buf[4] = {0};  //i2c received data buffer


	//void I2C_Write_EEProm(unsigned char slave_address, unsigned int memory_address, char * data, unsigned char DataLength )
	I2C_Write_EEProm(i2cAddress,0x00,"ABCDEFGHIJKLMNOP",15);

	//void I2C_Read_EEProm(unsigned char slave_address, unsigned int memory_address, char * data, unsigned char DataLength )
	I2C_Read_EEProm(i2cAddress,0x05,buf,5);  //reads three bytes starting at memory location 0x05 and returns the data into 'buf'
	UART_puts("READING: \r\n");
	UART_puts(buf);
	UART_puts("\r\n");



	__bis_SR_register(CPUOFF + GIE);        							// LPM0 with interrupts enable

} //end UART RCV ISR



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