MSP430G2553 PWM Control via I2C Communication

Hi Andrew!

First thing I have to say is that I'm not familiar with this GRACE stuff and I don't know which code snippets are generated by GRACE automatically and which is your own. To be honest - I don't like GRACE very much because this automated code generation may be easy, but in most cases you don't really learn how to set up your micro properly. But this is my opinion and I don't mind if people want to do so.

Some things in your code make me wonder a little bit. First is your RX/TX interrupts. Why do you use both? You're just receiving data, aren't you? Furthermore you're reading your received byte in the TX-ISR. This will never pop up I think. This could be the reason why your PWM stops after any transmission. Look at your RX-ISR and what you are doing in it - you are setting the "new" control bit. This RX-ISR will be called after you have received a byte, but you never read this byte from the RX-buffer because this is done in your TX-ISR. Your PRxData is propably all zero after startup and since copying the received byte from your RX-buffer to this array is in the TX-ISR PRxData remains zero. This zero is then copied to your timer-control in the timer ISR which stops it.

Next thing in your RX-ISR is that you do not wait for all bytes to be received, but you are changing divide, periodHigh and period in every RX interrupt even if byte 1, 2, 3 and 4 haven't been received yet. This will cause your timer to do things you do not want until all bytes came in. So work with a byte counter and set a flag after all data has been received and then change your settings.

Your timer ISRs look strange, too. For example TIMER0_A0_VECTOR has no TA0IV_TACCR1 - this belongs to TIMER0_A1_VECTOR. Same for the other timer. Maybe you read this:

http://e2e.ti.com/support/microcontrollers/msp430/f/166/p/381874/1346638.aspx#1346638

And why do you trigger on TAIFG? Why not using the hardware PWM with OUTMOD_7?

Dennis

To help you a little bit with your code:

// Your variables

unsigned char change_timer_flag = 0;

void main( void )
{
  // Configure your clock
  // Configure your ports and their functions
  // Configure your USCI
  ...
  // Setting up your timer
  TA0CCR0    =  1000;                // Period
  TA0CCR1    =  500;                 // Duty-cycle
  TA0CCTL1   =  OUTMOD_7;            // Reset/set
  TA0CTL     =  ( TASSEL_2 | MC_1 ); // SMCLK, up-mode

  TA1CCR0    =  1000;                // Period
  TA1CCR1    =  500;                 // Duty-cycle
  TA1CCTL1   =  OUTMOD_7;            // Reset/set
  TA1CTL     =  ( TASSEL_2 | MC_1 ); // SMCLK, up-mode

  // Enable global interrupts

  while( 1 )
  {
    // Do something else

    if( change_timer_flag )
    {
      switch( RxBuffer[0] & 0x01 )
      {
        case 0:
        {
          // Set your new settings for PWM 1
          break;
        }
        case 1:
        {
          // Set your new settings for PWM 2
          break;
        }
      }

      change_timer_flag = 0;
    }
  }
}

#pragma vector = USCIAB0RX_VECTOR
__interrupt void USCI0RX_ISR_HOOK( void )
{
  RxBuffer[RXByteCtr++] = UCB0RXBUF;
  
  if( RXByteCtr >= 5 )
  {
    RXByteCtr = 0;
    change_timer_flag = 1;
  }
}

If you want to power down your MCU you can do the code that is executed after the flag is checked in your RX-ISR, too, of course. But wait for all bytes to be reiceived.

Dennis,

Thank you for your help and I understand that you prefer not to use GRACE but I set-up the I2C communication using the suggestion given in the I2C section of the GRACE configuration interface. I have taken a screen shot of this and copied and pasted it below.

Thanks again,

Andrew

Dennis,

I made the changes that you suggested and now I seem to have issues with the I2C now even though I did not change anything that has to do with that. I have attached my code below and a screen shot of my I2C bus.

1538.PWMfromI2C.zip