msp430Fr6879: I2c interfacing

Hello Noble,

Thank you for your post. The "Solutions to Common eUSCI and USCI Serial Communication Issues on MSP430 MCUs" document covers I2C on page 10. This will cover the most common I2C issues and how to check for them and may help solve your issue. Let me know if you have any questions about the document.

Also, can you post the output from a logic analyzer or oscilloscope monitoring the communication lines when the devices are attempting to communicate?

Regards,

Matthew

                  The controller fails to properly generate the start or stop pulse, I assume that the controller is unable to drive the pins properly, since my program gets stuck after I call for a start condition or stop condition.and the ustp or the ucstt remains set, which as per my knowledge means that the controller couldn't complete generating a start or stop pulse. another peculiar thing is noticed is that when I connnect the CRO with the sda line the start or stop pulse gets generated.
  Kindly guide.
        

herin is my code 

#include <msp430.h>


volatile unsigned char TXData[] = { 0x00,0x12, 0x13, 0x14, 0x01,0x02,0x10,0x17};
volatile unsigned char TXByteCtr;
volatile unsigned char flag=0;
volatile unsigned int counter=0;
volatile unsigned char flow=0;
volatile unsigned char RxData[7];



void clockInit(void);

int main(void)
{
WDTCTL = WDTPW | WDTHOLD;

clockInit();
P6DIR |= BIT3;
P6DIR |= BIT2;

P6OUT &= ~BIT3;
P6OUT &= ~BIT2;



//_______________________________________I2C INITIALIZATION_______________________________________________
//------------------- Configure GPIO-------------------------------
P4SEL1 |= BIT6 | BIT7; // I2C pins
P4SEL0 &= ~(BIT6 | BIT7); // I2C pins
LCDCPCTL0 = 0x0000;

// Configure USCI_B0 for I2C mode
UCB1CTLW0 |= UCSWRST; // put eUSCI_B in reset state
UCB1CTLW0 |= UCMODE_3 | UCMST | UCSYNC; // I2C master mode, SMCLK

UCB1I2CSA =0x68 ; // configure slave address
UCB1BRW = 0x04; // baudrate = SMCLK / 2
UCB1CTLW0 &= ~UCSWRST; // clear reset register
UCB1IE |= UCTXIE + UCNACKIE + UCRXIE; // transmit and NACK interrupt enable

__bis_SR_register(GIE);

//________________________________________________END OF I2C INTIT_________________________________________________


__delay_cycles(3000000); // 250ms delay
//---------------flow = 0 => write time----------------------------------------------
flow=0;
TXByteCtr = 8; // Load TX byte counter

while (UCB1CTLW0 & UCTXSTP); // Ensure stop condition got sent
UCB1CTLW0 |= UCTR ;
__delay_cycles(120000);

UCB1CTLW0 |= UCTXSTT; // I2C TX, start condition

while(flag == 0);
flag=0;

__delay_cycles(3000000);
//---------------------------flow= 1 => write address pointer ----------------------------------------
flow=1;
TXByteCtr = 1; // Load TX byte counter

while (UCB1CTLW0 & UCTXSTP); // Ensure stop condition got sent


UCB1CTLW0 |= UCTR | UCTXSTT; // I2C TX, start condition

while(flag == 0);
flag=0;

//------------------------------flow 2 read time------------------------------------------------

flow=2;
TXByteCtr = 7; // Load TX byte counter


UCB1CTLW0 &= ~UCTR;
UCB1CTLW0 |= UCTXSTT; // I2C TX, start condition
while(flag == 0);
flag=0;
__delay_cycles(120);
while (UCB1CTLW0 & UCTXSTP){
UCB1CTLW0 &= ~UCTXSTP;
UCB1CTLW0 |= UCTXSTP;// Ensure stop condition got sent
__delay_cycles(120); // 12 usecs
}

while(1)
{
//---------------------------flow 1 write pointer ----------------------------------------
__delay_cycles(120);
flow=1;
TXByteCtr = 1; // Load TX byte counter
while (UCB1CTLW0 & UCTXSTP); // Ensure stop condition got sent
UCB1CTLW0 |= UCTR | UCTXSTT; // I2C TX, start condition
while(flag == 0);
flag=0;

//------------------------------flow 2 read time------------------------------------------------
__delay_cycles(120);
flow=2;
TXByteCtr = 7; // Load TX byte counter
// while (UCB1CTLW0 & UCTXSTP); // Ensure stop condition got sent

UCB1CTLW0 &= ~UCTR;
UCB1CTLW0 |= UCTXSTT; // I2C TX, start condition
while(flag == 0);
flag=0;
__delay_cycles(120);
while (UCB1CTLW0 & UCTXSTP){
UCB1CTLW0 &= ~UCTXSTP;
UCB1CTLW0 |= UCTXSTP;// Ensure stop condition got sent
__delay_cycles(120); // 12 usecs
}

}
}



#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector = USCI_B1_VECTOR
__interrupt void USCI_B1_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(USCI_B1_VECTOR))) USCI_B1_ISR (void)
#else
#error Compiler not supported!
#endif
{
switch(__even_in_range(UCB1IV, USCI_I2C_UCBIT9IFG))
{
case USCI_NONE: break; // Vector 0: No interrupts

case USCI_I2C_UCNACKIFG: // Vector 4: NACKIFG
UCB1CTLW0 |= UCTXSTT; // resend start if NACK

break;

case USCI_I2C_UCRXIFG0:
UCB1IFG &= ~UCRXIFG;
if(flow==2)
{
if (TXByteCtr) // Check TX byte counter
{ RxData[7-TXByteCtr] = UCB1RXBUF; // Load TX buffer
TXByteCtr--;
if(TXByteCtr==0)
{
UCB1CTLW0 |= UCTXSTP; // I2C stop condition
flag=1;
P6OUT ^=BIT2; // Decrement TX byte counter
}
}
}
break; // Vector 22: RXIFG0
case USCI_I2C_UCTXIFG0: // Vector 24: TXIFG0
if(flow==0)
{if ((TXByteCtr)) // Check TX byte counter
{ UCB1TXBUF = TXData[8-TXByteCtr]; // Load TX buffer
TXByteCtr--; // Decrement TX byte counter
if(TXByteCtr==0)
{ flag=1;
UCB1CTLW0 |= UCTXSTP; // I2C stop condition
UCB1IFG &= ~UCTXIFG; // Clear USCI_B0 TX int flag
P6OUT ^=BIT2;
}

}

}
if(flow == 1)
{ if(TXByteCtr)
{ UCB1TXBUF = 0x00; // Load TX buffer
TXByteCtr--; // Decrement TX byte counter
}
else { flag=1;
}
}
UCB1IFG &= ~UCTXIFG;
break;
default: break;
}
}

Hello Noble,

The document I posted above has steps to debug your setup. On page 2 there is general eUSCI information and debugging steps, and on page 10 there is I2C specific information and debugging steps. If you go through these steps with your project, you will most likely find the issue.

If you have access to one of them,  a logic analyzer or an oscilloscope will be extremely helpful in debugging your setup. If you'd like, you can post the output here and I will help you decipher it.

Additionally, you can find code examples for reference on resource explorer. Here is a I2C example for the MSP430FR6879, and there are several more there you can look through.

Regards,

Matt

hello MR. Matthew,

As you had suggested I went through the document and the code examples too.

I am more or less near to the issue this is what I have found,

Generally, the code runs fine.If in case by any fault (like a power off ) the communication is not completed that is a stop condition is not generated , the clk line is held low by msp430 controller, in turn, the busy flag and the scl low flag of the status register are set ,

now even after reinitializing(using reset) the module or restarting(power up) the entire board , the status flags still remain the same i.e. busy and clk low remain set . On further analysis on CRO it was found out that the data line remained low even after restarting the device and the clk line too,  both of which should actually be pulled up at the power on state. no sooner you touch the clk line with the probe it gets pulled up and along with that the data line also gets pulled up. and the device starts working again.

kindly help me with this.

Regards,

Noble Ajay.