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I2c help (very very basic)

Randy Yao
Prodigy 150 points
Other Parts Discussed in Thread: MSP430G2553

*updated

I'm trying to run this code to use an ADXL345 accelerometer using I2C communication with MSP430G2553. Thanks to the comments below, I made some changes.

Right now, please check if my main function has the right idea, and the i2c_start, i2c_init, and i2c_stop functions to see any errors.

Also, I connected the accelerometer as follows: Pin 1.6 as SDA, pin 1.7 as SCL, both with 10kOhm pull-up resistors. Do I need to pull any jumpers off the msp430 controller?

As well, how do you check the value of a variable in CCS?

Any help to the above questions are really appreciated, I'm pretty desperate. 

Thanks so much

Code:


#include <msp430.h>

#include <stdint.h>

 

void main(void) {

 

int ID = 0x1D; //device ID from the data sheet

      

i2c_init(ID);

i2c_start();

i2c_tx(ID); // it's possible to write multiple bytes in without stopping it right?

i2c_tx(0x3B); //on the datasheet it says "this translates to to 0x3A for a write and 0x3B for a read". Do I need this?

i2c_stop();

 

i2c_start();

int tID = i2c_rx(); // checking to see if communicating with device; how would you check what value tID is?

i2c_stop();

}

 

unsigned char i2c_rx()

{ 

while((UCB0STAT & BUSY)!= 0);

UCB0CTL1 &= ~UCTR; //Receive

UCB0CTL1 |= UCTXSTT;

while(UCB0CTL1 & UCTXSTT);

return UCB0RXBUF;

}

 

void i2c_tx(unsigned char data)

{

while((UCB0STAT & BUSY)!= 0);

UCB0CTL1 |= UCTR; // UCTR=1 => Transmit Mode (R/W bit = 0)

UCB0CTL1 |= UCTXSTT; // start condition generation

UCB0TXBUF = data;

__delay_cycles(200);

}

 

int i2c_init(unsigned char address)

{

  P1SEL=BIT6|BIT7;

  P1SEL2=BIT6|BIT7;

  UCB0CTL1=UCSWRST;

  UCB0CTL0=UCMODE_3|UCSYNC|UCMST; // check this

  UCB0CTL1=UCSSEL_2|UCSWRST; // check this

  UCB0BR1=0;

  //I tried values of 12 and 16 for this also

  UCB0BR0=10;

  UCB0I2CSA=address;

  UCB0CTL1 &= ~UCSWRST;

  while (UCB0CTL1 & UCTXSTP);

  //UCB0I2CIE = UCNACKIE;

  //IE2 = UCB0TXIE;

  return 0;

}

 

int i2c_start()

{

  //Address is now set in i2c_init instead of here

  //UCB0I2CSA = address;

  UCB0CTL1 |= UCTXSTT+UCTR;

  delay_ms(5);

  //while (UCB0CTL1 & UCTXSTT);

  return 0;

}

 

int i2c_stop()

{

  UCB0CTL1|=UCTXSTP;

  //while (UCB0CTL1 & UCTXSTP);

  delay_ms(5);

  return 0;

}

  • 0
    Guru 227245 points

    Randy Yao said:
    Something's wrong.

    What? Nobody will take the effort of chekcing your code without the smallest hint where to look. You should at least say what you expect and what you observe. A simple 'it doesn't work' won't enable anyone to remotely debug your problem.

  • 0 in reply to Jens-Michael Gross
    Prodigy 150 points

    I'm specifically asking for help in checking the functions (especially last function i2c_read()). 

    And if anyone see glaring errors in main it would be great.

    Thanks

  • 0
    Prodigy 140 points

    you have not declaration receiver and transmitter

    read:

    unsigned char i2c_rx()
    {

    while((UCB0STAT & BUSY)!= 0);
    UCB0CTL1 &= ~UCTR; //Recive
    UCB0CTL1 |= UCTXSTT;
    while(UCB0CTL1 & UCTXSTT);
    return UCB0RXBUF;
    }

    and write

    void i2c_tx(unsigned char data)
    {

    while((UCB0STAT & BUSY)!= 0);
    UCB0CTL1 |= UCTR; // UCTR=1 => Transmit Mode (R/W bit = 0)
    UCB0CTL1 |= UCTXSTT; // start condition generation
    UCB0TXBUF = data;
    __delay_cycles(200);

    }

  • 0
    Guru 227245 points

    In your main code, you use the read immediately after a write. Yout don't send a stop and start or repeated start with UCTR clear (so RXBUF jus tocntains a dummy value). And you don't wait until somethign is received.

    Reading RXBUF doesn't initiate an I2C read operation. It jsut returns the last received byte of an already running receive operation. You should re-read the I2C chapter of the users guide (especially the nice diagrams for master read and master write and what happens when.

  • 0 in reply to Jens-Michael Gross
    Prodigy 150 points

    Thanks for the suggestion. Do you mean I2C works like:

    Start

    write something

    write something else

    stop,

    start

    read,

    stop?

    Also do you mean I need to read the user guide for MSP430's I2c section? Couldn't find it on google =/

  • 0 in reply to Randy Yao
    Guru 227245 points

    Randy Yao said:
    Do you mean I2C works like:

    Basically, yes.

    I2C is transaction-based. A transaction begins with an 'hey, slave, I want to send you something' or 'hey, slave, I want to read from you'. The direction of the transfer is part of the slave addressing (this is why some I2C device manufacturers give two different 8-bit slave addresses for their slave, one for reading and one for writing, but actually, it is one 7-bit address and a R/W bit).

    So if you want to write, then read, these are two independent transactions, both with a separate start. (even though the stop between them can be omitted for a so-called repeated start)

    Randy Yao said:
    Also do you mean I need to read the user guide for MSP430's I2c section? Couldn't find it on google =/

    On the MSPs product page on the TI website, you can download the users guide (with a description of all modules found in any MSP of a family) directly below the download link for the device datasheet. In your case you'll need the 2x family users guide.

  • 0
    Prodigy 170 points

    How to check for above file. Data is sent is proper .

    I have Ds1307 as RTC . i wanna write date and time once . ANd i need to read data from RTC.(slave). How to check whether code is working or not.

  • 0 in reply to Akash Nayak
    Guru 227245 points

    Ajit nayak said:
    How to check whether code is working or not.

    By generating known input data and comparing the output to the expected output.

    In case of an RTC: write a time, wait some time, read the time and check whether the reading is the written time plus the elapsed time. If it is, code might be okay. If not, code is definitely not working properly.

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