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msp430 I2C issue

falling leaves
Prodigy 90 points
Other Parts Discussed in Thread: MSP-EXP430F5529LP

Hello,

I am using a MSP-EXP430F5529LP and a MSP-EXP430G2 for I2C test. The F5529 as a master receive data from G2553 as a slave.The code is examples  MSP430F55xx_uscib0_i2c_04 and msp430g2xx3_uscib0_i2c_05  from CCS

However,it does not work.And when a start condition is sent ，the UCNACKIFG of F5529 is set.What wrong did I do?

PS:I use two 10K Pull up resistors. Slave address is set as 0x48.Is it right? I have tested it as 0x24 and the result is the same. 

Thanks for your help. 

  • 0
    TI__Prodigy 690 points

    Several things come to mind. First are you trying to send a command from the F5529 to the G2553 and then have the G2553 respond back to the F5529? If so, how about trying just sending a command from the G2553 to the F5529? Also, make sure your hardware is correct. I would make sure that both boards have the same ground. In other words you should have three wires connecting the MSP-EXP430F5529LP to the MSP-EXP430G2. As far as the slave address, from my understanding you can set it to whatever you want whenever you initialize the USCI module. Hope this helps.

  • 0 in reply to Ricardo Zepeda
    Prodigy 90 points

    Thanks for your response,Ricardo.

    I neglected to make the two boards have the same ground. However,after I did that the F5529 program hang on the line "while(UCB0CTL1 & UCTXSTT)" just like that the  Pull up resistors are not used.

  • 0 in reply to falling leaves
    Prodigy 40 points

    Try Reading this documents...

    www.ti.com/lit/ug/slau412c/slau412c.pdf

    www.ti.com/lit/an/slaa382/slaa382.pdf

    www.ti.com/lit/an/slaa383/slaa383.pdf

     

    The documents explain in great detail how i2c works. Get the snippet of code and paste it to or project.

  • 0 in reply to falling leaves
    Guru 227245 points

    In master transmit mode, UXTXSTT won’t clear (the USCI won’t complete the start byte) unless you write the first byte to send to TXBUF or set UCTXSTP.

    falling leaves said:
    Pull up resistors are not used.

    What do you mean by this? Don'T oyu use hte internal pull-ups or don't you have external ones or none at all?

    Note that the internal pull-ups are way too weak for I2C. You need external pull-ups of 10k or less (for higher speeds, 4.7k or even down to 1k, the internal ones are ~40k). Also, on 5x family, the internal pull-ups are automatically deactivated if a port pin is in output direction.

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